When Do Species Interactions Matter and What Is the Economic Value of Ecological Information in Multispecies Fisheries?

Calls to account for ecological interactions and tradeoffs in fishery management have grown over time. Here, we examined the implications of ecological interactions for management, and measured the costs of assuming one type of interaction when in fact another interaction is present.  We develop a flexible delay-differential bioeconomic model based on cod and herring fisheries for multiple types of species interactions.  We incrementally add complexity to species interactions, from no interactions, cod predation on herring, linear herring predation on cod eggs, and non-linear predation on cod eggs that produces depensation. The latter case has been hypothesized to result in a regime switch whereby cod might not be able to rebuild even in the absence of fishing. We use pseudospectral collocation to solve for the optimal dynamic solution under numerous fishing histories and ecological interactions. We find small deviations in optimal management and net present value across the cases, implying that single-species management is not necessarily an inferior strategy. The exception to this result is when the fish stocks were severely overfished. In this case, single species management could suppress cod recovery and result in economic losses on the order of 20% over time.