Advancing fisheries analysis through the application of ecological foraging principles

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In public opinion, the health of a fishery is usually equated to maintaining or even increasing catches. However, experiences with Canadian herring and cod in past decades have shown us that this is not always true. The underlying fish populations that sustain our harvests are not always well reflected by the fish that are caught. Fisheries science has shown us many examples where populations “collapse” because sustained periods of decline were not detected quickly enough. One of the less studied influences that can mask population decline is the nature of fishing itself. Our commercial fish harvesters are very good at what they do. As a result, their catches (and catch rates) often remain high, even as fish numbers initially decline. Yet information from commercial fisheries is still the foundation of many of our population estimates.The proposed program questions many of the perspectives of classical fisheries analysis. Traditional analyses define catch rate in terms of the amount of fishing activity: catch per unit effort (CPUE). However, including effort in the measure of performance can mask catches that do not increase in proportion to effort. We will test for these effects with statistical methods looking at effects within entire fleets and at the level of individual vessels. Traditional analyses also assume that the CPUE of the intended species (the target) is the best indicator of changing abundances. However, this is the time when changes in CPUE should be buffered by fisher behaviour. My students and I will test the effectiveness of CPUE from outside of targeting periods in population estimates. The implications of fisher movement between neighboring populations are seldom considered in classical analyses. We will employ a recent theoretical development in our lab that unites ecological foraging principles to fishing activities : fisheries isodars. This will incorporate vessel movements into fishery assessments among neighboring population components and along the boundaries between them. All of these behavioural biases will be used to change the way that effort is used in state-of-the-art population assessment models. Finally, we will test for and simulate changing associations among vessels at sea (networks within fleets) in relation to the underlying fish distributions. This will lay the foundation for the future incorporation of changing fleet structure in population estimates.The proposed research program will transform the use of fishing effort in stock assessments. The research will provide a dynamic perspective of fishing effort that will improve the accuracy of fish population estimates and reduce the risk of misinterpretation of CPUE data that has contributed to fishery crises in the past.