How much evidence is required for acceptance of productivity regime shifts in fish stock assessments: Are we letting managers off the hook?

A difficult question often confronting fisheries assessment scientists and managers is whether or not to accept that a shift in stock productivity has occurred. This is particularly the case when a stock has remained at historically low biomass despite management intervention and when there is an expectation that there should have been a stock recovery. We outline a weight-of-evidence approach that provides a structured means to evaluate this question. The approach, which scores a range of attributes, was applied to five fisheries from the NW Atlantic and SE Australia, chosen to provide a range of supporting evidence, as well as different potential causal mechanisms for a productivity shift. Given the resulting scores for the example stocks, and whether a productivity shift has been accepted for those stocks, a score of between 7 and 12 indicated a level required for acceptance of a productivity shift. The approach has highlighted areas of future research that would improve individual species scores. It is hoped that the paper will encourage a more systematic examination of potential stock productivity shifts in assessments than has hereto been the case.