Estimating precautionary thresholds for US west coast fisheries
André E. Punt, University of Washington
Scientific advice regarding fisheries management actions is often based on the results of control rules, which quantify the relationship between monitoring data, or the outcomes from quantitative stock assessments, and changes to management regulations. The control rules aim to satisfy legislative requirements related to achieving an appropriate balance between the benefits to harvesters and the risk of unintentional depletion of the managed resource and any associated ecosystem impacts. In the US, control rules need to aim to avoid ‘overfishing’ with high probability so recent changes to the major US federal fisheries law has required the implementation of ‘buffers’ between the best estimates of the harvest level which will maximise long-term catches and the actual catch level. The types of control rules which are commonly applied to achieve these objectives is summarized, with a focus on how uncertainty is accounted for. An approach based on simulation is then outlined which can be used to evaluate the trade-offs among performance metrics for fisheries management for different ‘buffers’; where formally the buffers are the differences between the target catch level given perfect information and the set catch limit when only a fraction of the uncertainty related to estimating the target catch level is quantified. The approach is applied to the fishery for red king crab, Paralithodes camtschaticu, in Bristol Bay, Alaska. Specifically, the performance of different buffers is evaluated in terms of their impact on short- and long-term catches, discounted revenue, the probability of overfishing (i.e. the catch exceeding the true, but unknown, target catch), and the stock becoming overfished (i.e. in the case of crab mature male biomass, MMB, dropping below half of the MMB corresponding to MSY). The application, which formed the basis for actual management decision making for this stock, accounts for the complexities induced by joint State-federal management of the fishery and also for catches in fisheries other than the directed male-only pot fishery.