Optimal Multispecies Harvesting in Biologically and Technologically Interdependent Fisheries

Abstract

Single species management of multispecies fisheries ignores biological interactions in addition to important technological interactions resulting from the multiproduct nature of firms' production often to the detriment of the health of the ecosystem, the stocks of fish species, and fishery profits. This dissertation solves a dynamic optimization problem of maximizing the net present value from a three species fishery and uses numerical optimization techniques to determine the optimal harvest quota of each species given the biological and technological interactions. The model is then extended to the case of a nuisance species, a species that lowers the value of the fishery by negatively affecting the growth of other species in the ecosystem, and has little harvest value of its own. As approaches for ecosystem-based fisheries management are developed, results demonstrate the importance of focusing not only on the economically valuable species interact, but also on some non-harvested species, as they can affect the productivity and availability of higher value species.

This study uses the arrowtooth flounder, Pacific cod, and walleye pollock fisheries in the Bering Sea/Aleutian Islands region of Alaska as a case study and finds the net present value of the fishery is decreased from $20.7 billion to $8.5 billion dollars by ignoring arrowtooth's role as a nuisance species on the growth of Pacific cod and walleye pollock. The optimal subsidy on the harvest of arrowtooth summed over all years is $35 million dollars, which increases the net present value by $273 million dollars, after accounting for the subsidy.