TSGA IPA: understanding broadscale impacts of salmonid farming on rocky reef communities.
Aquenal Pty Ltd
The monitoring of salmon farms in Tasmania is more comprehensive than that in most other parts of the world and is based on rigorous and broad-ranging research and monitoring that has been ongoing for over 20 years. The success of this integrated research framework has been enhanced through very strong links between government, industry and researchers. Robust regulatory controls have been used to manage benthic impacts from salmon farming activities, and through the adoption of adaptive management strategies, organic loading effects from marine farming operations have been effectively managed using the environmental monitoring framework administered by the Tasmanian Government. The salmon industry-funded Broadscale Environmental Monitoring Program (BEMP) for the D'Entrecasteaux Channel region (which commenced in 2009) has further enhanced the understanding of impacts to include the detection of broadscale impacts to water quality and sediment health. The only marine habitats not subject to broadscale assessment of potential impacts from salmon farming are rocky reef communities. As the Tasmanian salmon industry expands, both in terms of production and growing areas, commercial and recreational fishing groups are concerned that their targeted fishing grounds, which are predominantly based around rocky reef systems, may be impacted by nutrient emissions released through marine farming activities. This proposal seeks to provide an immediate response to characterising reef community health prior to the development of new growing areas in south eastern Tasmanian waters.
1. Undertake analysis of subtidal macroalgal community survey data (2003-2014) at the Ninepin point and Tinderbox Marine Protected Areas
2. Characterise macroalgal community assemblages within south eastern Tasmanian waters to determine potential broadscale impacts from salmon farm developments in south eastern Tasmanian waters.
3. Communicate the status and health of rocky reef communities (based on objective 2) to broad industry and recreational stakeholder groups
Principal Investigator: Sam S. Ibbott
Key Words: Salmonid Aquaculture, rocky reef assemblages, macroalgae, macroalgal assemblages, nutrients, nuisance algae, broad scale impacts, environmental management
Summary: The strategic growth of the Tasmanian Salmonid Industry is contingent upon ecologically sustainable development. Current Tasmanian production is not meeting domestic demand, and the industry is in the process of expanding farming operations to meet strategic growth targets. While local scale impacts are well understood, the extent of broad scale environmental impacts from finfish farming needs to be better understood, especially in relation to nutrient emissions and their potential ecosystem effects on macro-algal community assemblages on rocky reefs. This report describes the results of analyses and surveys designed to examine patterns of change and characterise reef assemblages in south eastern Tasmania, where there is increasing concern as the salmonid aquaculture sector expands into more exposed waterways that overlap with traditional wild fishing sectors (such as abalone and rock lobster). The first part of the study used the existing Marine Protected Area (MPA) monitoring dataset to examine patterns of change in macroalgal communities in south eastern Tasmania between 1992 and 2015. The second component of the study included a field survey of rocky reefs, incorporating the MPA sites, along with additional sites chosen to better represent industry expansion into new growth areas. The study used a collaborative approach, with field work and data analysis carried out by Aquenal and Marine Solutions. Scientific support and supply of the MPA dataset was provided by IMAS.
This report describes the approach and results of the time series analysis and reef characterisation. Complexities associated with reef assessment and options for future monitoring are also addressed.
This study has provided an improved understanding of patterns of change on rocky reef communities in southeast Tasmania. The study provides an important contribution to continuation of the long term MPA dataset that can be used to assess broad scale changes to rocky reef communities in southeast Tasmania. Incorporation of new reef monitoring sites adjacent to recent or planned salmonid farm expansions also complements the MPA monitoring program, providing an important baseline and improved suite of assemblage types that can be used to investigate potential impacts of salmonid farming activities.
The current study also provides important insights into many of the issues surrounding effective monitoring of potential nutrient related impacts on macroalgal communities. For future monitoring activities, consideration should be given to broadening the spatial and temporal scope of the monitoring program, and developing a more targeted approach to tracking the abundance of nutrient indicator species.
One of the main limitations associated with the current study relates to the restricted spatial and temporal scope of reef monitoring. In particular, timing surveys to coincide with expected periods of ephemeral algal growth would improve understanding of potential nutrient related impacts on macroalgal communities. Incorporating additional sites in closer proximity to salmonid farming operations would also greatly assist interpretation of potential salmonid farming impacts.
One potential option to more cost effectively increase the spatial and temporal scope of algal monitoring activities would be to develop a more targeted survey method that focuses on the algal taxa that are recognised as indicators of nutrient enrichment (e.g. opportunistic green algae as identified in the current study). A rapid survey of nutrient indicator species could potentially involve assessment of algal epiphytes colonising the dominant canopy-forming algae at each site, with potential for inclusion of multiple depth ranges and different canopy-forming species.
Development of a rapid assessment method, whereby sites could be surveyed within a dive time of < 1 hour (compared to 4-5 hours using the method employed in the current study) has the potential to dramatically increase the spatial coverage of algal monitoring activities for a given budget. Assuming that an effective rapid assessment method can be defined, a sensible future monitoring approach would be to implement a targeted algal survey on a more frequent basis (e.g. 6 monthly), with the more detailed ‘Edgar-Barrett’ surveys conducted over longer time scales (e.g. every 3-5 years). While a targeted algal survey method will increase cost effectiveness of algal monitoring, including the ‘Edgar Barrett’ method in future monitoring activities is still considered vital. Proliferation of nutrient indicator species may eventually lead to structural change in macroalgal communities and detection of such changes necessitates the more detailed macroalgal assessment provided by the ‘Edgar Barrett’ method. There is also considerable value in using the ‘Edgar Barrett’ method to monitor the long-term MPA sites for the purpose of identifying broad scale changes in reef communities.