Eastern Victorian trawl fish biology and stock assessment
Final report
Eastern Bass Strait deep water trawl fishery stock assessment
Development of a spatially-structured model for stock assessment and TAC decision analysis for Australian abalone fisheries
Together, the state-managed abalone fisheries comprise one of Australia's most valuable fisheries worth over $125 million dollars per year. Whilst there are obvious differences among the fisheries in each state, all are managed in a very similar way with perhaps the most important restriction being the total catch removed each year by the commercial fishery (TACC). Historically, the TACC in many of the states has been changed in response to management or industry perceptions, with little attempt to incorporate the available biological information into the decision-making process. This has been in part caused by the lack of a sensible framework with which to condense the available biological information into advice concerning the likely risk and performance of different future TACC. In recent years, independent research in Victoria and New South Wales has started to formalise a very similar framework for TACC advice. Whist specific differences occur among the approaches in the two states, several fundamental similarities occur. These include the development of a length-structured, stochastic population model that can incorporate all available biological information and make forecasts of the likely effects of future TACC.
Several aspects of the biology and ecology of abalone complicate the assessment of their fisheries. Perhaps most importantly, the short-distance dispersal of larval abalone leads to dis-aggregated populations with a limited ability to re-populate depleted areas. Further, the ability of commercial divers to differentially exploit spatially-separated sub-populations allows them to maintain catch rates despite reduced stock abundance. To date, such spatial structure has not been incorporated in any framework used for TACC advice. This is despite the availability of spatially-structured programs monitoring changes in the abundance of abalone of different sizes that have been completed within Victoria, South Australia and New South Wales for several years and are proposed in the other states. Such programs provide the necessary information with which to make spatially-structured assessments of the likely risk and performance of different future TACC.
Final report
Stock discrimination of blue-eye trevalla (Hyperglyphe antarctica) from Australian shelf waters and offshore seamounts and New Zealand
Blue-eye trevalla is an important species in the South East Fishery. Blue-eye trevalla is taken in large quantities by the trawl and non-trawl sectors in south eastern coastal waters and around offshore seamounts. Despite the high value of this species in the trawl and non-trawl fisheries, however, there is limited information on the stock structure and appropriate management units. Bolch et al. (1993) concluded there was sufficient gene flow to prevent genetic differentiation between blue-eye trevalla off Tasmania, South Australia and NSW, but the sample sizes were small, there are limitations to allozyme electrophoresis (the method they used), and they did not sample fish from NZ. Ward and Last (1993) suggested that, given the known limitations of allozyme electrophoresis, further genetic studies based on mitochondrial DNA analyses and larger samples be undertaken. As a consequence, the relationship between fish caught off the south eastern Australian coast and those taken from offshore seamounts is unknown. The need to identify the stock structure of Blue-eye trevalla has also been identified as a high priority by the blue-eye working group and SEFAG.
In recent years, developmental trawl fishing has been occurring in the East Coast Deep Water (ECDW) fishery. Significant amounts of blue-eye trevalla have been caught in this fishery from grounds well to the east of 157ºE, and currently these fish are under the same quota restrictions that apply to the rest of the SEF trawl fishery. The large distances between the ECDW fishing grounds and grounds where most of the east coast blue-eye are caught has led fishers to question whether the ECDW fish can be considered part of the stock upon which the TAC was based. There is an urgent need to assess the stock structure of blue-eye trevalla caught throughout the SEF, the ECDW fisheries and New Zealand. The results from a study assessing the stock structure of this species will provide managers with information on potential management units.
A proposal to investigate the relationships between blue-eye trevalla caught in the ECDW zone and the SEF was submitted to AFMA in 2001, and although supported, it was not funded at this time for a number of reasons. In response to suggestions from AFMA, the MACs and SEFAG, it was decided that the proposal should be re-submitted in 2002. To address suggestions from industry and management groups that the stock structure of blue-eye needed to be evaluated over a much larger area, the extent of the project was expanded to include blue-eye samples from across south eastern Australia, including offshore seamounts (such as those off Tasmania, Norfolk and Lord Howe Islands) and New Zealand.
Final report
‘stock’ as those along Australia’s continental shelf.