Sustainable management of mixed demersal fisheries in the North Sea through fleet-based management—a proposal from a biological perspective

摘要

Cod, haddock, whiting, saithe, plaice, sole, and Norway lobster are main target species for the mixed demersal fisheries of the North Sea, Skagerrak, and eastern Channel. Management by total allowable catch has not been able to constrain exploitation of individual species, so the potential for a fleet-specific effort management system to reach the management objectives established for the stocks is simulated. Relative fleet-specific effort factors are estimated based on the sum of partial fishing mortalities of the species caught, weighted by the stocks at risk of reduced reproductive capacity. The strategy promotes the use of selective gear and levies non-selective gear. The factors were applied in medium-term simulations of the annual decision process in accordance with existing and proposed multi-annual management plans (including for cod recovery). Strict effort reduction would be required for fleets targeting cod, plaice, or sole (specifically large- and medium-mesh trawler fleets, beam trawlers, and gillnetters) for ～5 years, reducing the exploitation rates on all stocks substantially. Cod and plaice are predicted to recover by 2010 and cod catches to exceed recent levels continually, with the more selective longliners and some other gear types profiting most. Management objectives for cod dominate annual effort adjustments, resulting in substantial underexploitation of other stocks. However, even a 10% bias caused by non-compliance would largely halt cod recovery and the restoration of other stocks.