Management strategy evaluation for Australia’s east coast tuna and billfish fishery: progress update [SA WP08] Ann Preece, et al.

"WCPFC-SC5-2009/SA-WP-8"

Includes bibliographical references (p. 33-34)

"Australia’s Harvest Strategy Policy requires fisheries under the control of the Australian Commonwealth Government be managed by Harvest Strategies (HS) that lead to sustainable stocks and maximise economic productivity. Harvest strategies are also known as management strategies, management procedures and harvest control rules. They generally include the decision rule and the data and methods used to calculate recommended future management actions (e.g. changes to catch or effort). The Australian HS policy states that Management Strategy Evaluation (MSE) should be used to test the performance of alternative HS with respect to risk, biomass targets and limit reference points. The Eastern Tuna and Billfish Fishery (ETBF) operates on the East Coast of Australia. The catch consists of five main species (yellowfin, bigeye, albacore, swordfish and striped marlin). Using the agreed framework for the harvest strategy for the ETBF, we have evaluated a range of alternative HS specifications using simulation operating models. These operating models were initialised using population parameter estimates from Western Central Pacific Fishery Commission (WCPFC) stock assessments. There are inconsistencies between the intention of these assessments and our need for local ETBF parameter estimates, and these issues are discussed. We have attempted to represent a range of plausible states and dynamics of the target stocks without having to produce ETBF specific stock assessments. To evaluate whether a HS is likely to perform as envisaged, it is tested in operating models that encompass a wide range of uncertainties. We included uncertainty in assumptions about regional connectivity, migration rates, non-ETBF effort, ETBF effort creep, CPUE and recruitment variability and sampling error (among others). In the case of swordfish, we also included a wide range of assessment model uncertainty. This was also possible, to a lesser extent, for bigeye tuna and will be possible for other species as results from future work on assessment model uncertainty become available. HSs are evaluated against a more likely reference set of uncertainties, as well as a more extreme, but plausible, “robustness” set of uncertainties. These reference and robustness sets are different for each species. For each species, the performances of the various individual HS are shown as trade offs between biological risk and average catches and catch rates. On the basis of these comparisons, industry and management representatives have selected a harvest strategy specification for each species and these will be implemented in the ETBF in Nov 2009. This paper reports on operating model development and HS evaluations to date. The results so far indicate that the performance of the HS will be determined by a number of 2 species-specific fishery characteristics (e.g. stock structure, life history parameters, and the actions of international fleets), such that Australian domestic actions may have considerable capacity to effectively manage some species (swordfish and striped marlin), while unilateral domestic management actions might be largely ineffective for other species (e.g. bigeye and yellowfin). The paper illustrates the type of process that might be undertaken if the WCPFC decides to manage the Western Central Pacific Ocean fisheries using Management Strategy Evaluation."