Multispecies spatial assessment models for the British Columbia groundfishtrawl fishery

A multispecies spatial model is proposed for evaluation of trawl management strategies and tested with data from British Columbia groundfish. Minimum stock sizes are estimated for 16 species using spatial catch per unit effor t data; these data indicate that only small proportions of most stocks are exposed to fishing at any time and that exchange rates of fish between the grounds and other habitats are rapid. A gravity model for spatial effort al location predicts substantial side effects of marine protected areas or dis carding of particular species on nontarget species/grounds due to redistrib ution of fishing effort. Multispecies, multiground delay-difference models are used in conjunction with the gravity model for spatial effort distribut ion to predict long-term population responses to various regulatory strateg ies. This simulation suggests that species composition and spatial structur e of the fishery are changing slowly due to reduction in abundance of long- lived species, but rapid collapses of target stocks are unlikely due to spa tial redistribution of effort in response to local declines. We question wh ether quota management (individual vessel quotas) can be safely implemented due to extreme uncertainty about current stock sizes and suggest that a be tter strategy may be to simply denominate fishing rights as individual effo rt quotas while providing protection for sensitive stocks through carefully placed marine protected areas.