Research Document - 2004/134

Potential implications of differential size limits in the Dungeness crab fisheries of British Columbia

By Phillips, A., Z. Zhang

Abstract

Dungeness crabs are harvested by commercial, recreational and First Nations fishermen coast-wide. In recent years, intensifying commercial crab fisheries have made it difficult for recreational and First Nations harvesters to catch crabs in many areas. In the past, demands for increased crab fishing opportunities by these two sectors has been dealt with by closing specific areas to commercial harvest. Further closures will begin to impact the viability of some of the coastal crab fisheries.

Differential minimum harvest size limits are proposed as an alternative to isolated total closures to commercial harvest. The limits chosen are 165 mm, measured across the widest part of the shell, for recreational and First Nations harvest with minimum commercial size increasing to 170 mm. The biological ramifications of differential limits are investigated in this paper.

Examination of the current proportion of the crab population falling between the old limit of 165 mm and the proposed new commercial limit of 170 mm indicate that an initial loss to commercial harvest of 20-30% by number or 10-20% by weight in the first year of implementation of this proposed new harvesting scheme. Boundary Bay is an exceptional case where there would be an initial reduction in harvest of greater than 50% by numbers and 30% by weight. If crabs between the old size limit and the proposed new size limit are allowed to moult, a maximum of 20% will do so over a period of 3 years, and the modal size of those crabs will be approximately 198 mm. The commercial fishery will probably stabilize at the level of initial loss due to harvest of allocation crabs by aboriginal and recreational harvesters except for Boundary Bay, in which it may stabilize at 60%-70% of the current landing level.

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