International management of North Atlantic pelagic fisheries - The role of competing species and exploiters

This paper explores the economic and biological effects of exploiter and species interactions in a multiplayer, multispecies fishery. To this end, a partial ecosystem model for three key pelagic species in the Northeast Atlantic (Norwegian spring-spawning herring, mackerel and blue whiting) is developed and coupled with an economic model describing harvesting behavior of three major exploiters. We explore the effects on the fishery under assumptions on plausible interaction parameters between the harvested species and the type of management adopted by the exploiting countries. Single-species management is modeled by using three single-species models of the pelagic complex. Net present value is increased by over 20% when applying multispecies management in the cooperative case. Under non-cooperation there is always overfishing of all species compared to the global optimum, resulting in depletion of the mackerel stock and an almost 50% loss in net present value attainable from the aggregate fishery. Interestingly, under non-cooperation the effect of exploiters applying either single-species or multispecies management is rather small on the health of the stocks and on economic benefits.