Implications of Different Management Strategies Under Changing Climate

Management strategy evaluation (MSE) is the method of using simulation testing with feedback to examine how robust candidate management strategies are to error and uncertainty. Management strategies can be designed to attempt to satisfy desired, and perhaps conflicting, management objectives. MSE was used to assess the performance of the current management strategy and an alternative management strategy for the fishery for walleye pollock (Theragra chalcogramma) in the Gulf of Alaska (GOA), when recruitment was driven by climate. Management objectives include keeping the stock close to the management reference level, preventing overfishing, and achieving high and stable catches. The relationships between recruitment abundance and historical climate indices (and the uncertainties associated with these relationships) were characterized within a statistical age-structured population dynamics operating model that was fitted to data used in the GOA walleye pollock stock assessment. Projections into the future were based on the estimated relationships and predictions of the climate indices from the Intergovernmental Panel on Climate Change (IPCC) models, using the current or the alternative management strategy to determine catch limits. Management performance, with respect to meeting management objectives, decreased when recruitment was forced by climate, although the stock was kept near the reference level on average. In addition, the ability to estimate management-related quantities, such as spawning biomass, deteriorated markedly when recruitment was forced by climate.  The progress of the MSE for the fishery for Pacific cod (Gadus macrocephalus) in the GOA will also be discussed.