Trophic dynamics of the eastern shelf and slope of the South East Fishery: impacts of and on the fishery
The change in focus of fisheries management towards ecosystem-based management (Pitcher 2001) is a worldwide trend. Within Australia it is particularly evident in the requirements of the Environmental Protection and Biodiversity Conservation (EPBC) Act, and in the development of regional marine plans (RMPs) under Australia’s Oceans Policy. The former requires strategic assessment of the ecological impacts of fishing, including assessing trophic impacts. The latter seeks to integrate management of entire regions through an ecosystem approach that considers impacts from all uses of the marine environment (including impacts of other users on fishery ecosystems). The southeast region is the first to be evaluated under Oceans Policy.
Even without the “stick” of EPBC and RMP, there are good reasons to attempt to synthesize current data and understanding of the SEF ecosystem, and to model the impacts of and on the fishery. Specific questions that need addressing include:
·What changes in the fish community have taken place in the past, and what are the consequences for current fishery production and value?
·What further changes might be expected under planned reduction or elimination of discarding in the SET?
·What are the implications for the fishery of current rapid recovery in seal populations?
·What are the reasons for and impacts of year-to-year variability in the SEF ecosystem (including regional circulation and primary productivity) on distribution and catches of quota species?
This study will provide a set of tools to explore answers to these questions.
Final report
Estimation of mortality rates from tagging data for pelagic fisheries: analysis and experimental design
Data from conventional tagging experiments have been and are becoming increasingly important for providing estimates of mortality rates in the stock assessment of large pelagic fishery resources as they provide a powerful, and perhaps only, alternative to relying on CPUE indices of abundance. There is an extensive scientific literature on tag-recapture experiments; however, a comprehensive framework for the analysis and design of tagging experiments in the pelagic fishery context does not exist. This has meant that in the design phase of tagging experiments, it has not been possible to provide scientifically rigorous advice on matters such as the relative tradeoffs between the number of tags to release, the spatial/temporal distribution of tags and the levels of observer coverage (required for estimation of reporting rates and for estimating the size/age distribution of the commercial catches). In addition, a comprehensive analysis of the extensive data from past SBT tagging experiments (particularly those conducted in the 1990s) taking into account all of the major potential sources of heterogeneity has not been completed because of the lack of a comprehensive estimation framework. Thus, the full benefit of the large research investment from these experiments has not been realized. It is also anticipated that conventional tagging programs will be a major future source of assessment information in both the eastern and western tuna fisheries. As such, an appropriate framework for the design and analysis of tagging experiments is needed to ensure that the full value from both past and future experiments is realized. Finally, there is increasing data accumulating from archival tags. There is a need to understand the role, and the relative cost/benefits, that archival tags can contribute to the overall estimation of mortality rates to past and future conventional tagging experiments.