Browsing by Author "Davies, Campbell R"

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    Performance review of simple management procedures
    (International Council for the Exploration of the Sea, 2015) Carruthers, Thomas R; Kell, Laurence T; Butterworth, Doug S; Maunder, Mark N; Geromont, Helena F; Walters, Carl; McAllister, Murdoch K; Hillary, Richard; Levontin, Polina; Kitakado, Toshihide; Davies, Campbell R
    Using a management strategy evaluation approach, we compare a range of new and established management procedures (MPs) for setting catch-limits in fisheries. Performance is evaluated with respect to fish life history type, level of stock depletion, data quality, and autocorrelation in recruitment strength. We quantify the robustness of each MP with respect to the various observation processes. Methods using observations of absolute biomass or stock depletion offer the best overall performance and this is consistent across life history types, data qualities, and stock depletion levels. Simple MPs can outperform conventional data-limited methods and data-rich assessments that use time-series of catch and effort data. MP performance is most sensitive to biases in catch data. Our results indicate that often tuning MPs for specific stocks is important, though this may not be viable in data-poor assessment scenarios because of insufficient data and analysis resources.
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    A scientific alternative to moratoria for rebuilding depleted international tuna stocks
    (Wiley, 2015) Hillary, Richard M; Preece, Ann L; Davies, Campbell R; Kurota, Hiroyuki; Sakai, Osamu; Itoh, Tomoyuki; Parma, Ana M; Butterworth, Doug S; Ianelli, James; Branch, Trevor A
    There is considerable international concern and scientific debate about the current state and future of tuna stocks worldwide and the capacity of Regional Fisheries Management Organisations to manage the associated fisheries effectively. In some cases, this concern has extended to predictions of imminent collapse with minimal chances of recovery, even under a commercial catch moratorium. As a viable alternative to a full fishery closure, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) has adopted a scientifically tested, adaptive rebuilding strategy for the depleted southern bluefin tuna (Thunnus maccoyii) stock. The management procedure (MP) adopted involves a harvest control rule that fully specifies the total allowable catch as a function of key indicators of stock status, adjusting future harvest levels every three years so as to meet the rebuilding targets agreed by CCSBT. It was chosen from a subset of candidate MPs selected following extensive simulation testing. This involved first selecting a wide range of plausible scenarios for stock status and input data, ranging from pessimistic to optimistic, against which the alternative candidate MPs were tested to ensure that they were robust to important uncertainties. This is the first time that a comprehensively evaluated MP has been adopted for an internationally managed tuna stock. Both the process and the outcomes have broad applicability to other internationallymanaged stocks.