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2. parameters determining population dynamics, & potential annual yields, for commercially important spp of demersal fish at depths between 400-700m in the underdeveloped sector of eastern Bass Strait

Development of a spatially-structured model for stock assessment and TAC decision analysis for Australian abalone fisheries

Project number: 1999-116

Project Status:

Completed

Budget expenditure: $499,175.00

Principal Investigator: Harry Gorfine

Organisation: Agriculture Victoria

Project start/end date: 11 Jul 1999 - 21 Jun 2005

TAGS

SPECIES

Need

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.

Objectives

1. Develop an appropriate modelling framework to incorporate all relevant biological information into a spatially-structured assessment of the likely risk and performance of different future TACC for an abalone fishery.

2. Develop the necessary software to complete such an assessment, and modify it to incorporate differences among the states and species.

3. Evaluate the capabilities of the modelling framework.

4. Compile the necessary data and complete a preliminary assessment of each state's abalone fishery.

Final report

ISBN: 1-74146-133-2

Author: Harry Gorfine

Final Report • 2005-05-20 • 2.05 MB

1999-116-DLD.pdf

PROJECT NUMBER • 2002-094

PROJECT STATUS:

COMPLETED

Using information for 'data-rich' species to inform assessments of 'data-poor' species through Bayesian stock assessment methods

ORGANISATION:

Agriculture Victoria

TAGS

Wild Catch

PROJECT NUMBER • 1999-103

PROJECT STATUS:

COMPLETED

Saw shark and elephant fish assessment and bycatch evaluation in the southern shark fishery

ORGANISATION:

Agriculture Victoria

TAGS

Wild Catch

SPECIES

Sawsharks

Stock discrimination of blue-eye trevalla (Hyperglyphe antarctica) from Australian shelf waters and offshore seamounts and New Zealand

Project number: 2003-045

Project Status:

Completed

Budget expenditure: $269,037.00

Principal Investigator: Jeremy Hindell

Organisation: Agriculture Victoria

Project start/end date: 30 Aug 2003 - 30 Apr 2006

TAGS

Stock Assessment

Laboratory Procedures

SPECIES

Need

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.

Objectives

1. To use otolith microchemistry and shape analyses to assess the stock relationships between blue-eye trevalla caught in 8 regions (east , west and south Tasmania, west Victoria/South Australia, east Victoria and East Coast Deep Water, Queensland/NSW shelf waters and the west coast of New Zealand)(YEAR 1).

2. To a) validate the results from otolith microchemistry and shape analyses, and b) better assess stock structure of blue-eye trevalla in the regions identified in objective 1, using mitochondrial DNA analyses (YEAR 2).

3. To determine a suitable approach for assessing stock structure in blue-eye trevalla in south-east Australia, and make recommendations on the most appropriate methods for future work (including sample size and spatial/temporal sampling), to better understand the stock structure of blue-eye trevalla in the SEF and ECDW fisheries.

4. To utilise the results from all analyses in the assessment and management of blue-eye trevalla via meetings of the relevant stakeholder groups including SETMAC, SENTMAC, AFMA and the blue-eye working group.

Final report

ISBN: 1-74146-575-3

Author: Jeremy Hindell

Final Report • 2006-12-13

2003-045-DLD.pdf

Summary

This work is principally about identifying the best method for examining the population structure of blue-eye trevalla (Hyperoglyphe antarctica). It is not, and was never intended to be, an exhaustive assessment of stock structure of blue-eye trevalla in Australia’s Fishing Zone. As such, findings on stock structure per se are preliminary only.

Blue-eye trevalla are a key economic species in Australia’s Fishing Zone. They are caught from NSW, around Tasmania, to Western Australia. Blue-eye are caught in both the trawl and non trawl fishing sectors, within which they are regarded as non-target and target species, respectively. The total allowable catch in 2004 was 743 tonnes across the non-trawl and trawl sectors, but only 651 tonnes were actually caught. Nonetheless, this catch had an estimated market value of more than $5 million AUD (based on average prices paid at the Sydney Fish Market). Less than 1% of blue-eye landings were discarded across the fisheries. The non trawl catch in 2004 was 567 tonnes, compared to 84 tonnes taken in the trawl sector. Most of the non-trawl catch is now taken by long lines off the east coast of Tasmania; since 2002 there has been a decline in the catch taken on drop lines. Since 1999 there has also been a decline in catches of blue-eye in the trawl sector.

Blue-eye trevalla are managed as a single stock. Research to date supports this management regime. Results from previous work on genetics (allozyme analyses) suggest that gene flow is sufficient to prevent genetic differentiation among fish collected from seamounts off NSW to those off Tasmania, and around the Tasmanian coast. Tagging studies suggest that juvenile fish (around 50 cm length) can move from NSW slope waters to those off eastern Tasmania; still smaller individuals (< 20 cm in length) can possibly drift between Australia and New Zealand. Despite this evidence, there is some uncertainty in whether fish from offshore seamounts, particularly those in the East Coast Deep Water, are the same
‘stock’ as those along Australia’s continental shelf.

This study used 4 different approaches (otolith shape analysis, otolith elemental microchemistry, otolith stable isotope analysis, mitochondrial DNA) to compare which method best delineated subpopulations of blue-eye sampled from 6 regions of the South East Fishery (SEF: NSW, east Victoria, east, south and west Tasmania, and South Australia), the East Coast Deep Water region, and New Zealand – 8 regions in total.

Samples of fish were collected opportunistically from commercial landings in each of these regions. Only fish with a fork length of approximately 50 cm or less were used. This enabled us to restrict the age of the fish we sampled, thereby ensuring that patterns among regions were a reflection of differences in stock structure rather than age. We collected at least 40 samples (individual fish) from all of the regions except NSW, from which we could only collect 30 fish (20 of which were of the ‘correct’ size). For each fish, we recorded the fork length, identified the sex (where possible), removed the otoliths for shape and microchemical analyses, and took tissue samples for genetic analyses.