The SBT resource is estimated to be at historically low levels and biological concerns exist about the status of the stock (Anon. 1998, 2001). There is also large uncertainty about the sustainability of current catches. The advice from the CCSBT Scientific Committee’s stock assessment in 2001 was that under current catch levels there was a ~50% chance that the stock would continue to decline or increase. The 2002 CCSBT Scientific Committee concluded that there was no basis for changing its previous advice on catch levels. The current management practice in the CCSBT is based on a global total allowable catch (TAC) with no consideration or restriction on where the catch is taken. Genetic studies, along with the fact that there is only one known SBT spawning ground, have led to the conclusion that SBT comprises a single reproductive stock. However, tag return and catch distribution data suggest that there may be substantial spatial structuring and incomplete mixing of SBT among the major feeding areas. Spatial structuring of the stock would have large implications for SBT assessments and for managing the rebuilding of the SBT resource. The combined results from the SRP conventional tagging program and this proposed archival tagging project would provide the basis evaluating the need for and, if necessary for developing, spatially-explicit population assessment and management response.

There is a critical need for direct and improved estimates of juvenile fishing mortality rates (or equivalently recruitment) to reducing uncertainty in the stock assessments and to provide a robust evaluation of the sustainability of recent catch levels. The SRP conventional tagging program is intended to provide this information. However, in order to achieve this objective, it is essential that sufficient information is available to account for incomplete mixing and the spatial dynamics of SBT in the analyses of the results from the conventional tagging data.

Catch-per-unit-effort (CPUE) indices are used to provide stock indicators of trends in the SBT stock size and form an essential input into the analytical stock assessment models. Interpretation of CPUE data is complicated by spatial and temporal variation in the availability and catchability of SBT in relationship to fishing effort. Interpretation of catch rates has been and continues to be a major source of uncertainty in the SBT stock assessment. The CCSBT Scientific Committee have repeatedly identified the need to develop alternative approaches for modeling and interpreting the SBT catch and effort data and this need has been incorporated into the agreed CCSBT SRP. Both availability and catchability are expected to vary with environmental conditions that modify the habitat suitability for SBT. Information for habitat-specific CPUE standardization was recognized as an important alternative approach for modeling catch rate data at the last CCSBT Scientific Committee meeting. This standardization approach takes into account changes in environmental conditions so that CPUE indices reflect the actual SBT habitat. This should allow the indices to more clearly reflect the actual changes in the abundance of SBT. This is especially critical as CPUE indices are seen as providing one of the key inputs in the decision-rule-based management procedure under development by the CCSBT. Thus, it is essential that to the extent possible that the CPUE indices provide a reliable indication of shorter term trends and that the CPUE signal is not confounded by short-term environmental fluctuations. Archival tags provide a unique tool for collecting the required habitat-specific requirements of SBT. Without such data, these habitat based standardization approaches are intractable. For example the archival tag data on vertical and horizontal distribution allow habitat preferences to be estimated, and CPUE standardization is possible.

In summary, this project aims to provide information to provide a substantial improvement in our current understanding of SBT movements and spatial dynamics. In particular, the proposal has been developed in response to three specific needs for an improved understanding of SBT spatial dynamics:
1. Estimation of mixing rates for the estimation of mortality rates from conventional tagging (particularly in the context of the large scale juvenile tagging program which is a high priority component of the CCSBT Scientific Research Program);
2. Habitat definition to allow the standardization of CPUE indices for use in the CCSBT stock assessment process; and
3. Requirements within the guidelines under the strategic assessment provisions of the Environmental Protection and Biodiversity Conservation Act 1999 that “the distribution and spatial structure of the stock(s) has been established and factored into the management response”.
In addition to these three specific needs, there is a general need to ensure that the current stock assessment models are robust to their implicit assumptions about spatial homogeneity.

This research aims to improve the product quality (the colour and flavour shelf-life (shelf-life)) of farmed SBT, which is perceived by the Japanese market to be shorter than wild tuna. The main aim in farming SBT is to produce a product that is high in lipids and this is achieved by feeding baitfish that is itself high in lipids, which may be rancid thus accelerating rancidity in farmed SBT. Improving the shelf-life of farmed SBT will provide an advantage for the Australian product be a high fat product, with the additional benefit of an extended post mortem window of sale (ie shelf life).
Previous experiments on the Tuna Research Farm by Thomas and Buchanan and others, has demonstrated that:
• feeding SBT pellets fortified with boosted levels of vitamin E, C and selenium will raise the level of these natural anti-oxidants in the fish muscle and the appropriate colour of sashimi grade tuna flesh is retained for longer.
• pellet feeds with higher levels of Vitamin E, C, and selenium were more effective in extending the shelf life of SBT flesh than those with a higher level of vitamin E alone.
• baitfish coated with vitamin E, C and selenium was also effective in raising the fish tissue level of vitamin C however, it was less effective at raising the tissue level of vitamin E and selenium.
• SBT with a higher tissue level of vitamin C had a sightly extended shelf life compared to those not fed fortified baitfish.
• a combination of higher levels of Vitamin E, C, and selenium increases colour shelf-life and stabilises the muscle activity of glutathione peroxidase (one of the key antioxidant enzymes).

There is now a need to improve the shelf life of farmed SBT which can be achieved by (1) gaining better understand oxidative protection systems in SBT and (2) adapting our field experiment results and diagnostic tools to the commercial environment.
This can be achieved by:
• developing an alternative method of anti-oxidant delivery which can be used within the existing commercial feeding system.
• use of in vitro cell culture techniques to gain a better understanding of oxidative protection system in SBT and as a rapid and cost-effective method of assessing vitamin supplement formulations that have the potential to improve flesh quality and extend shelf-life.
• use surrogate experiments to obtain basic information on the level of oxidative products that require specific antioxidant feed supplementation use and as an intermediate step in the application of invitro findings to commercial SBT farming.

This research will provide valuable information on the effects of oxidized feed on flesh quality and also baseline information on the oxidative status (i.e. degree of rancidity) of farmed SBT fed currently available feeds. It will provide diagnostic tests for industry to monitor the oxidative status of fish feed and farmed SBT.
The current proposed research is focused on product quality and will continue our investigations into the physiology, nutrition and muscle biochemistry of SBT that underpins developments in tuna husbandry. This project will utilise project 2001/248 results including the current adopted PhD students research. The project recruit a PhD student to the tuna quality project and will continue to support collaborative ties between Flinders University (Adelaide), CSIRO (Geelong), SARDI and the South Australian SBT industry.
This proposed research addresses the South Australian Fisheries and Aquaculture Research and Development Strategy 2002-2007 in the following areas:
Program 2 Industry Production –
Post Harvest enhancement/supply chain management
Farm husbandry and the nutrition of farmed species

This Project is essential for the development of a cohesive research and development approach aimed at meeting the priority needs of the SBT Aquaculture Industry. The industry has developed rapidly since its initiation in 1990 and has the opportunity to continue to do so; however targeted research and development is needed to underpin this development and to assure the long-term sustainability of the industry in an increasingly competitive international market.

This project provides the basis for the SBT Aquaculture Subprogram (and Aquafin CRC Production and Value Adding Programs that the Subprogram Leader also leads). The Subprogram includes a management structure to oversee the active research projects and ensure they achieve the desired outcomes; provides a focused strategy for disseminating research results to industry and obtaining feedback; and setting research priorities. This project ensures that the minimum level of duplication occurs in the provision of research services; provide a focus for SBT aquaculture research and sucessional planning of key persons; addresses industry priorities by establishing a mechanism to empower industry's involvement in their research; establishes a framework to ensure that SBT aquaculture research is orderly and targeted; and disseminates, where appropriate, research information to stakeholders.

Opportunities also exist for the development of further research proposals targeted at other research and development funding agencies (eg. AusIndustry). For instance, the Program Leader has recently worked with David Ellis, TBOASA, and two tuna farming companies to submit AusIndustry Start Graduate Grant Applications. These, if successful, will facilitate the active involvement of two of the small companies interested in applying the Aquafin CRC research outcomes in a commercial setting and undertaking in-house research activities.

This project provides a mechanism for identifying priorities, quality research providers and opportunities, as well as coordinating and facilitating grant applications. This project provides the resources to ensure that the projects within its portfolio achieve the desired outcomes. This responsibility represents, over 4 years, an investment of $525,344 towards the overall management of approximately $8.5 million research and development, which is the Aquafin CRC-FRDC funding commitment to SBT aquaculture research over this time period.

The SBT aquaculture industry is very successful and has rapidly grown to exceed $300 million per year. This industry is, however, facing greatly increased competition from recently developed tuna aquaculture in Spain, Malta, Italy, Croatia, Turkey and Mexico. The increased global production of farmed tuna saw a significant drop in returns to Australian growers in 2003. A targeted research and development program is essential to maintain the competitiveness of the Australian tuna industry.

In September 2003 the SBT Aquaculture Subprogram Steering Committee reviewed the previous project (2002-249), which provided research services to projects utilising live tuna for experiments. The committee directed that the Tuna Research Farm be closed and two modified projects be submitted:
A) A project covering the scientific involvement of Dr Jeff Buchanan in the existing research projects increasing his time on science.
B) A new project to be developed by David Ellis covering the use of a commercial tuna farm to hold live tuna for experimental purposes.

This combination was expected to deliver better research outcomes and maximise uptake of results by industry.
The ongoing areas of research priority include, nutrition, product quality, physiology, environmental sustainability and health.

Current FRDC-CRC projects addressing these priority areas (Projects 2001/249, 2001/248, 2001/103 & 2003/228) will be supported by this project.