261 results

Indigenous business development opportunities and impediments in the fishing and seafood industry - 'Wave to plate' establishing a market for Tasmanian cultural fisheries

Project number: 2016-204
Project Status:
Completed
Budget expenditure: $255,195.00
Principal Investigator: Marcus Haward
Organisation: University of Tasmania (UTAS)
Project start/end date: 29 Dec 2016 - 29 Nov 2018
Contact:
FRDC

Need

Aboriginal wild catch is aspirational, seasonal and culture-dependent. For these reasons, it does not compete well against large-scale, industrial fishing operations. Addressing the FRDC’s Indigenous Sector strategy to improve understanding and engagement that ‘best support individual and community economic development’ (FRDC 2015), this project aims to develop a niche market of boutique seafoods, together with investigating how the arts and tourism sectors can foster fisheries management for greater Indigenous community benefit.

A Tasmanian Aboriginal engagement framework in fisheries has not yet been developed by government (Lee 2016, in press). This project will create the conditions for extensions development, based upon resetting engagement terms between Indigenous peoples and government, providing a toolkit of self-determining strategies for regional development. Economic models for future development of fisheries can build upon the capacity of Indigenous communities to translate value into benefit in subsequent projects, such as employment opportunities within the network chain of wild catch procurement to presentation.

There is a need to provide best practice guidance that demonstrates Australia’s commitment to international obligations, such as 2007’s UN Declaration on the Rights of Indigenous Peoples. In Australia, building on the growing jurisprudence that affirms native title rights to land, the High Court in 2013 extended such rights to commercial fishing in the Torres Strait in its Akiba v Commonwealth decision (Butterly 2013). However, judicial recognition of Indigenous fishing or other marine-based rights does not in itself provide specific guidance on how those environmental resources should be managed culturally and economically.

Objectives

1. Adapt successful terrestrial model to marine environments, investigating specific conditions of Tasmanian Government policy relating to Indigenous peoples.
2. Assess cultural fishery extensions within commercial operations and determine best practice for government and industry partners.
3. Explore the network chain opportunities for Indigenous involvement in food tourism.
4. Develop postgraduate Indigenous research capacity and broaden scope of marine studies in academia.

Final report

ISBN: 978-1-925761-09-2
Author: Emma Lee and Marcus Haward
Final Report • 2019-05-01 • 4.86 MB
2016-204-DLD.pdf

Summary

The FRDC project, ‘Wave to Plate’: establishing a market for cultural fisheries in Tasmania, is the first time that an Aboriginal Tasmanian postdoctoral researcher has engaged with marine research in Tasmania. Indigenous-led research has delivered a raft of outcomes that can be considered important social shifts for Tasmanian Aboriginal fisheries in over a generation, and, at the time of writing, the Tasmanian Government is actively working to implement the outcomes of the project in relation to access to resources and good governance.
This project has been successful in highlighting the barriers to participation and engagement in cultural fisheries, specifically the current regulatory and policy frameworks that impede progress towards regional development and the contributions that cultural economies of Aboriginal Tasmanians can make to the Tasmanian state. It has identified gaps in knowledge and posited future research directions that are Indigenous-led and centred upon connections to sea country. The project has also been successful in publicly demonstrating the appetite for cultural fisheries through the trialling of the ‘Wave to Plate’ concept with commercial partners.
 
There has been increased understanding from government, Aboriginal communities, industry and research stake holders and partners to the potential of new markets and developmental fisheries from making centre and core Aboriginal Tasmanian connections to sea country. New collaborations with food tourism interests have resulted from the project to inject cultural strengths into Tasmanian fisheries.
This report outlines several key areas that must be considered for establishing a market for cultural fisheries in Tasmania. These include:
  • access to marine resources for Aboriginal Tasmanians;
  • the governance forms, such as a proposed Indigenous Fisheries Advisory Committee and cultural marine planning unit, to assist in decision-making that provide fairness, equity,transparency and opportunities for Aboriginal Tasmanians to develop cultural fisheries that suit local conditions;
  • the models for Indigenous rights to resources and business enterprise that provides a best fit for Aboriginal Tasmanian regional development and fisheries management;
  • the research directions that require a multi-disciplinary focus; and
  • the types of partnerships that can aid in the establishing a market for cultural fisheries.
The report demonstrates that there is a vast array of good will towards Aboriginal Tasmanian aspirations and a variety of means upon which the direction of fisheries can deliver mutual benefit. Above all, there is a breadth and depth of Aboriginal Tasmanian community expertise to create a new industry based upon ancient traditions.
Industry
PROJECT NUMBER • 2016-177
PROJECT STATUS:
COMPLETED

Phase 2: Traceability Systems for Wild Caught Lobster, via Sense-T and Pathways to Market

This document is the final report of the project (FRDC 2016-177) ‘Traceability Systems for Wild Caught Lobsters’. It has been prepared by researchers from University of Tasmania. Background The project ‘Traceability Systems for Wild Caught Lobster, via Sense-T and Pathways...
ORGANISATION:
University of Tasmania (UTAS)

Vulnerability of the endangered Maugean Skate population to degraded environmental conditions in Macquarie Harbour

Project number: 2016-068
Project Status:
Completed
Budget expenditure: $421,129.00
Principal Investigator: Jeremy Lyle
Organisation: University of Tasmania (UTAS)
Project start/end date: 31 Mar 2017 - 30 Jul 2020
Contact:
FRDC
SPECIES

Need

The physio-chemical conditions in Macquarie Harbour have changed markedly since European settlement and the general decline in DO since 2009, which occurred at the same time as the rapid expansion of marine farming operations, is likely to have had a significant impact on many resident species, including the endangered Maugean Skate. Given the species poor ability to cope with low DO, any reductions in bottom DO concentrations are expected to directly influence the distribution of the skate, highlighting the need to better understand the oxygen demands of the species. Current generation acoustic tags capable of measuring DO and activity in the field, which when combined with laboratory studies, represent methods to examine tolerance and responses to varying levels of DO. Bottom DO also has implications for the development and survival of skate eggs. Limited information suggests that eggs are deposited at depths of > 20 m where they are likely to be increasingly exposed to low DO concentrations. An understanding of the relationships between environmental conditions and the development and survival of embryos, coupled with the depths in which eggs are deposited, has particular relevance to assessing the implications of changing environmental conditions on future recruitment and productivity of the Maugean Skate population.

Furthermore, the ability to monitor the status of this population, especially given the rate and extent of recent environmental changes in Macquarie Harbour is critical to assess its future viability. Tracking size composition, including data from previous studies, has the potential to provide a baseline against which reduced recruitment (if linked to the changed environmental conditions) could be detected.

The maintenance of best environmental practices by the aquaculture industry supported by effective monitoring and environmental management policies represent essential requirements if industry and Maugean Skate populations are to coexist.

Objectives

1. Determine the distribution of Maugean skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
2. Examine the relationship between environmental conditions and survival and viability of Maugean skate eggs.
3. Determine what DO levels Maugean skate experience in Macquarie Harbour, particularly when in deeper waters.
4. Determine the physiological costs of the DO levels Maugean skate are exposed to in Macquarie Harbour.
5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.

Final report

ISBN: 978-1-922352-39-2
Authors: David Moreno Jeremy Lyle Jayson Semmens Andrea Morash Kilian Stehfest Jaime McAllister Bailee Bowen and Neville Barrett
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.
Final Report • 2020-10-01 • 3.41 MB
2016-068-DLD.pdf

Summary

Maugean Skate (Zearaja maugeana) are only known from two isolated estuarine systems located on the west coast of Tasmania, representing one of most restricted distributions of any elasmobranch. There is, however, uncertainty about the continued persistence of the species in one of these estuaries (Bathurst Harbour), suggesting that Macquarie Harbour may now represent the sole remaining habitat for the species.  The species is listed as Endangered under the Threatened Species Protection Act (Tas) and the Environmental Protection and Biodiversity Conservation Act (Comm) and, apart from protected status, is without a recovery plan or management strategy. 
The physicochemical conditions in Macquarie Harbour have changed markedly since European settlement, influenced by anthropogenic activities in and around the estuary (e.g. mining, forestry, hydro-electricity generation, and marine farming operations) as well as the more general effects of climate change.  Of recent concern, has been a marked decline in dissolved oxygen (DO) conditions in Macquarie Harbour which are likely to have a significant impact on many resident species, including the Maugean Skate.  In the absence of population dispersal or mixing outside of Macquarie Harbour, any longer-term changes to DO conditions in the harbour are likely to result in changes to ecological assemblages inhabiting this unique estuarine system. The current study describes the vulnerability of the Maugean Skate, across all its life history stages, to a range of environmental stressors. The ability to monitor population status and population responses of the Maugean Skate to any changes in environmental conditions will be critical in assessing the need for further conservation management action. 
Objectives
The primary aim of this study is to establish the mechanistic links between the environmental conditions experienced by the Maugean Skate across multiple life stages and the implications of the changing environment in Macquarie Harbour.  Specific objectives include:
  1. Determine the distribution of Maugean Skate eggs within Macquarie Harbour, with particular reference to depth and bottom DO.
  2. Examine the relationship between environmental conditions and survival and viability of Maugean Skate eggs. 
  3. Determine what DO levels Maugean Skate experience in Macquarie Harbour, particularly when in deeper waters.
  4. Determine the physiological costs of the DO levels Maugean Skate are exposed to in Macquarie Harbour.
  5. Assess the potential of using the size composition of Maugean Skate catches as an indicator of population change, in particular recruitment variability
  6. Assess the implications of declining DO concentrations in Macquarie Harbour on the future viability of the Maugean Skate population.
Methodology
The study comprised five main components: (1) systematic field surveys of skate egg distribution, (2) laboratory study of embryo development; (3) field assessment of skate behaviour in relation to environmental conditions; (4) laboratory assessment of physiological responses to conditions experienced in the wild; and (5) fishery-independent surveys to examine the potential to inform on changes to population status.

A combination of beam trawl and dive surveys was employed to sample for Maugean Skate egg cases in areas of known high skate abundance.  Egg capsules collected in the field were reared in the laboratory to describe embryonic development and gestation period.  Acoustic telemetry was used to examine links between environmental conditions (i.e. dissolved oxygen and temperature) and the distribution, movement and habitat use of the Maugean Skate within Macquarie Harbour. An acoustic array comprising 52 acoustic receivers was deployed in the Table Head/Liberty Point region of Macquarie Harbour and 25 adult Maugean Skate were externally tagged with multi-sensor acoustic tags capable of continuously transmitting information on the depth, temperature and dissolved oxygen concentrations experienced by the individuals over a 12-month period. Physiological trials were conducted in a purpose-designed field laboratory to examine physiological responses to low DO and low salinity exposure, replicating environmental conditions experienced by the skate in Macquarie Harbour.  Gillnet surveys were undertaken to extend the time series of Maugean Skate size composition data and evaluate its potential as an indicator of changing population status.  

Key findings
Maugean Skate eggs were found across a wide range of depths (2.5 - 33 m) but appear to be most abundant in relatively shallow sites (< 10 m). Based on an analysis of the condition of egg-capsules, hatching success was estimated to be about 40%, which is comparable to success rates reported for other temperate skate species.  An egg reared under laboratory conditions hatched 31 weeks (~ seven months) after oviposition.  Respiratory channels opened after 15 weeks, exposing the embryo to external environmental conditions for over half of the gestation period.  These findings indicate that, depending on the depths at which eggs are deposited in the wild, embryos will experience a range of dissolved oxygen, salinity and temperature conditions, reflective of localised fluctuations in environmental conditions.  The implications of these varying conditions for development and survival are unknown.

This study represents the first use of animal-borne acoustic sensors to monitor long-term dissolved oxygen conditions experienced by a coastal elasmobranch and the links with behaviour. The results showed that skate are subject to wide ranging fluctuations in water chemistry. For instance oxygen levels experienced ranged from normoxic (50-100%), hypoxic (20-50%) and to near anoxic (~0-20%), with individuals often experiencing substantial variation (as high as > 90%) in the range of DO levels within the same day.
Adult Maugean Skate exhibited a high level of site selectivity and site fidelity across a relatively small spatial extent and with a strong preference to depths between 7.5 and 12.5 m. Despite individual variation in long-term residency, noting that several individuals appeared to permanently exit the study area, the tagged skate showed a clear preference towards the Table Head and Liberty Point areas. Furthermore, home ranges calculated using continuous time movement models showed a high degree of spatial overlap in the core home ranges (50% utilisation distribution, UD) of each of the individuals.  Their extended activity areas (95% UD) did, however, change throughout the year corresponding to variation in environmental conditions.  For instance, a sharp increase in surface water temperature and declines in mid- and deep water dissolved oxygen levels during summer resulted in all detected individuals spending time at shallow depths before returning to their preferred depths. While the shallow sites provided access to improved oxygen conditions, higher temperatures and exposure to hyposaline conditions will place an increased metabolic demand on individuals, potentially driving them to continuously move back into deeper waters where temperature and salinity conditions are more stable.  A large storm surge and subsequent oxygen recharge in March/April 2019 resulted in all tracked individuals expanding their extended activity areas considerably, including movement into deeper waters, while still maintaining a strong attachment to their core areas.
The present study shows that there is an intricate link between movement of the Maugean Skate and environmental conditions in Macquarie Harbour. The species appear to behaviourally modulate environmental stressors through movement, likely balancing optimal habitat requirements against the energetic cost of chronic hypoxia in deeper waters and increased thermal and osmoregulatory stress at shallow sites. Such behavioural plasticity may constitute a key adaptation that to date has enabled the species to tolerate such a challenging environment that Macquarie Harbour represents.  However, since individuals continued to utilise the same core UD and preferential depth range, despite these areas being subject to the largest daily fluctuations in water chemistry conditions experienced by the skate, this behavioural plasticity appears to be limited to their extended use areas. Therefore, the site attached behaviour of the skate suggest that these core sites likely provide an advantage that outweighs the cost of exposure to unfavourable environmental conditions, such as access to prey that may not be as readily available elsewhere within the estuary. 
Physiological experiments demonstrated that adult Maugean Skate are quite capable of surviving chronic exposure to hypoxic conditions (< 20% DO) by using metabolic depression as a survival strategy. Metabolic depression does, however, occur at the cost of other energy intensive life history processes, such as growth, foraging and reproduction.  As such, metabolic depression cannot be sustained long-term, and as a result skate may seek oxygen in the shallower waters of the harbour where they will encounter hyposaline conditions.  Maugean Skate are unusual in that they are the only known species of skate to live exclusively in a euryhaline environment (areas with a wide range of salinities) and, based on the range of depths utilised, are constantly exposed to a wide range of salinities.  Routine metabolic rate appeared to be higher following acclimation to hyposaline conditions, although the corresponding statistical test only showed near-significance.  Since individuals appear to utilise shallow areas as a DO refuge during the summer months, they will also be exposed to higher temperatures which in turn will result in further metabolic stress. 
Physiological data based on a single individual suggests that neonates are oxyconformers (rate of oxygen consumption dependent on environmental DO), implying that even at an early age, Maugean Skate may be able to tolerate short-term hypoxic events through an increased reliance on anaerobic metabolism. The point below which oxygen uptake became negligible in the neonate was higher (~ 66% DO) compared with adults (10-25% DO), implying a lower tolerance threshold which could have important implications for survivorship of early life stages, especially in relation to the range of environmental conditions experienced in Macquarie Harbour.
During this study, an unexpectedly high proportion of tagged individuals died.  Although causality cannot be established, the timing of these events suggest that the mortalities were unlikely to have been a direct consequence of tagging.  Most mortalities (8 out of 11) were clustered in two discrete periods that corresponded with marked changes in environmental conditions within the core habitat used by the skate. In addition, behavioural changes (based on change point analysis) were observed at the same time in virtually all surviving individuals.  It is feasible, therefore, that the deaths may have been related to stress caused (directly or indirectly) by the significant changes in the environmental conditions of the harbour. If this is the case, then recent changes in the environmental health of the harbour (especially dissolved oxygen levels), coupled with the consequences of climate change (including occurrence of extreme weather events), may already be challenging the skate’s capacity to cope with the environmental conditions in Macquarie Harbour.
Deriving an estimate of the effective population size of the Maugean Skate in Macquarie Harbour has proven challenging and there is a high degree of uncertainty associated with current estimates that limit their applicability in monitoring the continuing status of the population. An analysis of research gillnet data collected since 2012 suggests a reduction in the relative abundance of juvenile and sub-adult individuals and as well as an increase in the size of the larger individuals (adults) in the catches through time.  Despite uncertainty as to the significance of the size composition data in terms of representing trends in population status, a recent decline in recruitment, possibly due lower hatching success or juvenile survival, coupled with adult growth represent plausible scenarios that could produce the changes observed.  
Implications
This study provides a greater understanding of the ecology and life history of the Maugean Skate and describes for the first time some of the behavioural and physiological adaptations that have enabled the species to survive in such a unique and challenging environment as Macquarie Harbour. Our results suggest that the species can mitigate some environment variability by a combination of behavioural (movement) responses and physiological capability.  However, the vulnerability of early life stages to the changing environmental conditions, long-term changes in the size structure of the population, and the mortality of some tagged individuals following significant environmental events collectively highlight the vulnerability of the Maugean Skate in Macquarie Harbour and the need to consider further conservation action to support the persistence of this unique micro-endemic skate. 
In addition to addressing uncertainties around the apparent changes in the size (and age) structure of the population through further research fishing, there is an urgent need to investigate cost-effective and non-invasive approaches to estimate population size and mortality rates, which can be applied to track population status and health over time.  Importantly, managing the known anthropogenic impacts on the environmental health of Macquarie Harbour, both in terms water column and benthic conditions, will ultimately prove crucial to the success of any conservation strategy for the Maugean Skate. A multi-stakeholder and holistic environmental management approach for Macquarie Harbour should be considered as part of this strategy.

Social Science and Economics Research Coordination Program (SSERCP)

Project number: 2015-300
Project Status:
Completed
Budget expenditure: $160,416.00
Principal Investigator: Emily Ogier
Organisation: University of Tasmania (UTAS)
Project start/end date: 28 Feb 2015 - 27 Feb 2018
Contact:
FRDC

Need

Phases I&II of the SSRCP successfully raised awareness of the need for, and increased the use of, social science fisheries research to improve fisheries and aquaculture sector outcomes. SSRCP I&ll also highlighted the need for a social sciences reference group for FRABs, researchers, industry and managing agencies, and for coordination of social science fisheries research.

Across this same period the societal needs and drivers impacting marine resource management have increased in importance (Barclay 2012; Mazur, Curtis et al. 2014). Further research activity is needed to address challenges regarding the social impacts, acceptability and sustainability of fisheries and aquaculture and to better integrate research across the social sciences (including economics) and between social and biological sciences. The 2014 FRDC Social Sciences Survey indicated broad support for continuation of SSRCP activity and highlighted the Program’s role in linking social science research outputs with decision-making and representations of the industry, brokering collaborations and in facilitating the uptake of FRDC’s key national interest projects.

While there is clear need for continuing the activities that have been the SSRCP’s remit, there is the scope to extend the suite of activities by working closely with the 'FishEcon' project and, post- 30/06/15, with its legacy activities (in particular the FishEcon Network). Such a partnership will result in efficiencies in the delivery of project activities, including newsletters and other networking activities, and in project administration; provide the opportunity to develop tighter integration between economics and the social sciences in research, extension and capability building.

Objectives

1. Support the FRDC to meet relevant objectives as outlined in its 2015-2020 RD&E Plan and the National Fishing and Aquaculture RD&E Strategy, as well as other needs arising from FRDC's existing programs and projects
2. Collaborate with the industry and managing agencies to identify emerging issues in wild harvest, aquaculture, post harvest, recreational and indigenous fishery sectors and the associated key social science and economics research needs
3. Co-ordinate and undertake the communication of key social science and economic research needs to the research community and research outcomes of the Program to fishers and management agencies.
4. Provide program management for social science and economics projects to ensure quality and relevance by undertaking evaluation and review of project proposals, and milestone and final reports.
5. Build further capability in fisheries social sciences and economics research to meet the needs of industry and managing agencies in addressing emerging issues in wild harvest, aquaculture, post harvest, recreational and indigenous fishery sectors

Final report

Author: Emily Ogier and Sarah Jennings
Final Report • 2018-01-01 • 644.67 KB
2015-300-DLD.pdf

Summary

The SSERCP project has been successful in providing timely and relevant advice to the drafting and reviewing stages of RD&E priorities, projects and reports in order to maximise beneficial outcomes of this investment for fisheries and aquaculture. It has been successful in supporting the FRDC and researchers in completing a number of high profile, high impacts projects (including the Social and Economic Evaluations of NSW Coastal Fisheries and Aquaculture, 2014-301 and 2015-302, and Beyond GVP 2013-301). It has also been able to establish strong working networks with leaders of other FRDC subprograms and a number of the RACs and IPAs. Capability in economics has been increased under the project, through the Higher Degree Research student projects commenced under the FishEcon project, and the delivery of the Masterclass in Fisheries Economics to managers and industry representatives alike.
 
The implications of the SSERCP have included:
• Establishment of a trusted multi-disciplinary reference group for industry, management agencies and research providers alike
• Improved collaborations, efficiencies and impact in delivering the social science and economic RD&E that FRDC stakeholders seek
• Improved networks and capability amongst researchers and professional members of industry and government able to deliver and adopt the social science and economic RD&E required
• A way forward for developing and expanding engagement activities by industry and government to address issues arising from reduced social license and acceptability, based on best available information (the ‘License to Engage handbook’)
 
Major recommendations arising from the SSERCP mid term evaluation include:
• That the FRDC should continue to support the coordination of social science and economics RD&E for fisheries and aquaculture; and, specifically,
• That the FRDC establish a social sciences and economics research subprogram with funds to allocate to RD&E, and in the design of such a subprogram:
  o Seek further mechanisms to consult and collaborate with the RACs and IPAs;
  o Improve the extension and adoption of major social science and economics RD&E project outputs; and
  o Increase awareness of its role and the role of social science and economics RD&E across the broader FRDC membership.
Environment
PROJECT NUMBER • 2015-024
PROJECT STATUS:
CURRENT

Managing ecosystem interactions across differing environments: building flexibility and risk assurance into environmental management strategies

Summary The overarching aim of this research was to provide an improved understanding of the environmental interactions of Atlantic Salmon farming and to provide recommendations to both government and industry on monitoring and management strategies that are appropriate to the level of risk...
ORGANISATION:
University of Tasmania (UTAS)
Blank
PROJECT NUMBER • 2014-726
PROJECT STATUS:
COMPLETED

SCRC: Measuring condition of lobsters to improve management of harvesting around periods of high transport mortality

This project provides the first comprehensive quantitative assessment of the health, physiological and nutritional condition of brindle and red lobsters from four different fishing areas of Tasmania at the start of the 2015 fishing season. Lobsters size (carapace length), baseline concentrations of...
ORGANISATION:
University of Tasmania (UTAS)
Industry

Reassessment of intertidal macroalgal communities near to and distant from salmon farms and an evaluation of using drones to survey macroalgal distribution

Project number: 2014-241
Project Status:
Completed
Budget expenditure: $61,915.04
Principal Investigator: Christine D. Crawford
Organisation: University of Tasmania (UTAS)
Project start/end date: 19 Jan 2015 - 30 Dec 2016
Contact:
FRDC

Need

The proposed expansion of salmon farming to new sites in south eastern Tasmania earlier this year has already elicited opposition from some neighbouring residents, wild abalone fishers and environmental groups, which has been well displayed in the media. One of their major concerns is lack of information on whether salmon farms are affecting intertidal and subtidal macroalgae, and no ongoing monitoring of these habitats. This highlights the importance of repeating the survey eleven years later to assess changes in intertidal macroalgal abundance and species composition around salmon farms.

Drones are increasingly being used to record agricultural environments, including salmon farms. However, methods to quantitatively assess coastal environmental change using drones, such as macroalgal distribution and abundance have not been assessed. The effectiveness of this technique to monitor salmon farms is needed to maximise usage of this data and before it can be incorporated into monitoring programs.

This project will provide information important to several FRDC Strategic Priority Areas.
• Program 1: Environment: Themes 2 and 4: Habitat and Ecosystem Protection and Ecologically Sustainable Development, especially providing information to the community to demonstrate improvements in the aquaculture industry’s environmental performance and quantifying the environmental carrying capacity of aquaculture operations.
• Program 2: Industry: Theme 6 and 7: Resource Access and Allocation, and Production, Growth and Profitability, especially increasing knowledge among diverse groups of stakeholders about each other’s expectations for resource access and allocation, and increase and diversify opportunities for the aquaculture sector.
• Program 3: Communities: Theme 10: Resilient and Supportive Communities, especially understanding and influencing the community perceptions about the fishing and aquaculture industry and improving interactions between them, and increasing the community’s capacity to accept and incorporate higher levels of aquaculture activity.

Objectives

1. To repeat the assessment of intertidal macroalgal composition and abundance near to and distant from salmon farms in the Huon and D’Entrecasteaux Channel region eleven years after the initial assessment.
2. To evaluate the potential of using Unmanned Aerial Vehicles (drones) to monitor macroalgal distribution.

Final report

ISBN: Print 978-1-925646-20-7 Online 978-1-925646-21-4
Author: Christine Crawford and Stephen Harwin
Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Final Report • 2018-07-05 • 3.59 MB
2014-241-DLD.pdf

Summary

The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.

In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.

Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.

The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.

Environment
PROJECT NUMBER • 2014-032
PROJECT STATUS:
COMPLETED

Improved understanding of Tasmanian harmful algal blooms and biotoxin events to support seafood risk management

The 2012 Tasmanian biotoxin event represents a paradigm shift for seafood risk management in Tasmania and Australia as a whole. The causative dinoflagellates are extremely difficult to identify by routine plankton monitoring, and are toxic at very low cell concentrations (50-100 cells/L). Sampling...
ORGANISATION:
University of Tasmania (UTAS)
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