Evaluating fisheries management options under large systematic changes in predator-prey interactions

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The quantitative models most commonly applied to provide fisheries management advice presume stability in ecological conditions governing fish population dynamics over long periods of time. In many regions there have been very large systematic trends in key species that prey on fishes and large fluctuations in key prey species. There has been considerable theoretical modeling research into studying the possible impacts of predator-prey interactions on commercially and recreationally valuable species. However, there has been relatively little attention given to developing stock assessment modeling approaches and management strategy evaluation (MSE) approaches that can offer direct advice to fisheries managers and policy makers in situations where there have been large apparent changes in key prey and predator species of key recreational and commercial fishes. I seek to investigate the influence of systematic changes in predator-prey interactions on fish population dynamics for a variety of Canadian fisheries in which there appears to have been substantial changes in the prey and predator populations. I will do so using a MSE approach in which I will build new population dynamics models of fish populations that account for the possible influence of changes in predator and prey populations in a number of Canadian fisheries where there have been substantial recent changes in key predator and/or prey species populations. I will seek to test hypotheses about the possible effects of changes in predator species abundance and predation rates on natural mortality rates and changes in prey species abundance on changes in growth rates for these fish populations. The long-term objective of my proposed research program is thus to investigate the influence of predator-prey interactions on fish populations using the framework of management strategy evaluation (MSE). I seek to develop population dynamics models, use Bayesian statistical techniques to test hypotheses about the influence of predator-prey interactions on the population dynamics of harvested fish populations and apply these models in MSEs to identify policy options that are robust to scenarios for plausible changes in future predation rates and prey availability. I plan to test the hypotheses that large systematic changes in (a) pinniped (e.g., seal species) population abundance and (b) forage species availability will modify the influence of fisheries exploitation on the population dynamics of harvested fish populations via changes in, e.g., growth and natural mortality rates (M). To undertake the research I will investigate how (1) spatial heterogeneity and historic and possible future trends in predation risk and the abundance of prey species can jointly modify (a) the population dynamics, (b) the maximum sustainable yield (MSY) reference points that are commonly used to guide policy advice, and (c) the suitability of different management approaches for a variety of harvested fish species. In addition I will investigate (2) how management approaches can be designed to adapt to systematic changes in the abundance of key predator and prey that may modify a fish stock’s resilience to exploitation. I plan two case studies: Project #1: Using an MSE approach to evaluate policy options for chronically-depleted B.C. inside water rockfish stocks. Project #2: Using a MSE approach to evaluate policy options for an apex predator under large changes in forage species abundance: Lower Fraser River white sturgeon. In these case studies, scenarios on how systematic changes in key predator and prey populations can affect fish stocks will be assessed in order to identify fisheries monitoring and harvest control policy options that respond appropriately to such changes.