Prawn resources underpin some of the most economically important fisheries in Australia and form the basis of very important recreational fisheries. Ecologically sustainable development of fisheries resources partly depends on catching species at optimal sizes and there is considerable concern that the gears being used in NSW’s commercial and recreational prawn fisheries catch them at sizes smaller than that which optimises biological yield.

Prawn fisheries in NSW (and the world) have attracted enormous attention in the past few decades over their by-catch of non-targeted species – especially juvenile fish. In NSW, this led to the development, implementation and legislation of various gear-based solutions like the Nordmore Grid and square mesh panels (see attached publication list). A major by-catch issue remaining for NSW’s prawn fisheries concerns the by-catch and discard of unsaleable sizes of school and king prawns. Currently, large numbers of small prawns are discarded well after capture (sometimes even after cooking) through the process of “riddling” which involves passing the prawn catch over a sieve to separate large and small individuals. This is considered a major waste of a resource – especially since it is known that, for fast-growing prawns, undersize individuals could be expected to reach a desirable size in a relatively short time. Unfortunately, virtually no research has been done on the selectivity of school and king prawns in any of the gears used to catch them (i.e. prawn trawls, haul nets, set pocket nets and snigging nets in commercial fisheries; and dragnets and scoop nets in recreational fisheries). All are thought to catch large numbers of very small school and king prawns that are discarded well after capture. If excluded from nets underwater, these prawns should, in a relatively short period of time, provide substantially improved catches of the more desirable and valuable sizes of prawns.

In 1998, Broadhurst, Larsen, Kennelly and McShane developed a codend made entirely of small square mesh to reduce the discards of small western king prawns in Gulf St Vincent, South Australia. The current application is for funds to develop full square-meshed codends and other methods to decrease the discard of small prawns throughout the many commercial and recreational prawn fisheries of NSW.

There are major concerns over the status of the garfish species in NSW waters, particularly eastern garfish and river garfish. These commercial fishery for these species is considered to be threatened.

For example, landings of river garfish from NSW estuaries peaked at over 100t in 1974/75 but have steadily declined since that period. In the past decade, on average less than 30t per year of this species are caught.

In addition, there has been a sudden and dramatic drop in the catches of eastern sea garfish in the last decade, from 280t in 1992/1993 to only 29t in 1999/2000.

While increasing fishing pressure is one possible cause for these declines in catches, another major concern is the impact of coastal development on the habitats of these species, which appear to have a strong reliance on key estuary and inshore habitats, such as seagrasses (see Background). The continued deterioration of these key inshore habitats in NSW is considered to be another significant impact on the commercial catches.

Unfortunately, despite over a century of exploitation, little is known about the biology, life history, or habitat requirements of these two NSW garfish species and no research has been conducted on the fishery itself. With the dramatic drop in catches and the concern about the degradation of key estuarine habitats, there now exists an urgent need to carry out research on the garfishes in NSW waters, particularly on the two exploited species, eastern sea garfish and river garfish.

In this joint project carried out by the University of Wollongong and NSW Fisheries, we propose to address this research gap, by providing information on the biology and life history of these two NSW species of garfish, and make recommendations that will help to achieve sustainability of this medium sized, but lucrative fishery.

Freshwater allocations to sustain fisheries

The 1994 COAG Water Reform Agreement and various state legislation (e.g. Water Act 2000 in Queensland) requires managers to allocate water to maintain downstream ecosystem health. One aspect of ecosystem health is estuarine and coastal fisheries production. Information on the role of freshwater in maintaining the productivity of commercial and recreational fisheries is needed to ensure that estuaries and their stakeholders are duly represented in the water allocation processes. Natural resource managers (fisheries and water) need to be made aware of the fishing industry’s vulnerability to the impacts of non-fishing activities, such as water regulation. This issue has been identified as a challenge for the fishing industry in reaching sustainable production (see Challenge 1 of FRDC’s R&D Plan 2000, page 59).

Logical frameworks for research leading to new procedures and methods

A logical framework needs to be developed for investigating the role of freshwater flows in estuaries. Procedures to assess the impacts of current and proposed water infrastructure in Australian coastal rivers on estuarine fisheries need to be developed. Methods for monitoring biological responses to environmental flows are needed to provide feedback to managers as to whether desired fisheries-related outcomes are being achieved under current water allocations.

Enhancing the research outcomes - integrating across research disciplines

An integrated research program is needed to develop a robust sampling proceedures that can investigate the role of freshwater flows in estuaries and the impacts of modified flows on fisheries production. The CZCRC offers the opportunity to integrate flow-influenced fisheries data with other hydrological (i.e. costal modelling) and primary productivity (i.e. nutrient cycling) research projects that will provide greater insight into ecosystems processes.

Recent concern regarding the status of east coast Spanish mackerel has been expressed by both commercial and recreational sectors and fisheries biologists. Further, an assessment of the stock status of east coast Spanish mackerel is a very high priority of resource managers. A recent preliminary assessment of the east coast mackerel stock conducted by QDPI suggested high fishing pressure maybe at a limit reference point for the stock. To refine the current assessment and allow for greater certainty of future stock assessment, more fish age data combined with an extensive description of the exploitation dynamics (the methods and gears used by fishers) of the east coast stock are urgently required. A critical need exists for the documentation of the exploitation dynamics and biological characteristics (catch-at-age, catch-at-length and sex ratios) of both the recreational and commercial sectors for the major catch regions of the entire east coast where no data are currently available.

Stock assessment of Queensland Spanish mackerel is core business of the QDPI long-term monitoring program. The opportunity to collaborate and build upon this initiative of QDPI is now available. The data collected by this project collaborated with that of the long-term monitoring project would allow the age data required for stock assessment to be provided with greater certainty. Further, this project will provide data that will expand the current understanding of the exploitation dynamics of the east coast stock. Combining these project outputs with the current knowledge base will allow resource managers to proceed with changes to the current management regime, where they are required, with greater confidence than is currently available.

The swordfish fishery has expanded rapidly in the past few years off eastern Australia with an annual catch now of ~2400 tonnes. When the fishery first began AFMA set a ‘trigger’ point of 800 tonnes, after which they would review the amount of fish taken. Similar rapid growth has been reported for the fishery for swordfish off Western Australia where the catch is now at ~1000 tonnes. Added to this is the developing New Zealand fishery now also reaching 1000 tonnes. This last point is relevant in that recent genetic evidence indicates a single stock encompassing all three fisheries (Reeb et al 2000). There is an urgent need, therefore to determine whether these catches are sustainable. However, the population parameters from which accurate stock assessment can be made have not yet been determined for the Australian region. To this end Eastern Tuna MAC and SWTBF MAC listed age and growth determination as priorities three and one respectively in their list of ten priority research issues. The latest meeting of the Standing Committee on Tuna and Billfish (SCTB 13) held in Noumea noted the increase in swordfish fishing in the Western Central Pacific Ocean. They listed age and growth as a priority research issue for this species.

Assessments require input data on mortality, longevity and age structure; estimates that can be obtained from age and growth studies. There is a clear need therefore, for an age and growth study of this species. However, without validation over a number age classes, incorrect interpretations have lead to the wrong decisions by management. Therefore, before such an ageing study is begun the first priority is validation of the annual cycle of growth. With appropriate validation a length at age key, which is presently lacking, could be provided.