Exploitation and Mortality of Male Dungeness Crabs (Cancer magister) Near Tofino, British Colombia

Abstract

Male Dungeness crabs (Cancer magister) were sampled by traps and monitored by tagging as they moulted and entered the fishery near Tofino, British Columbia, from April 1985 until March 1987. Males first recruited to the fishery after moulting from the μ = 129-mm CW (carapace width) to the μ = 156-mm CW normal instar. Sublegalsized males (< 154 mm notch-to-notch CW) in the μ = 156-mm CW instar (≈ 42% of this instar) were found to have a high annual natural mortality (M = 2.9–4.5), with < 10% surviving to legal size. Legal-sized males experienced high annual fishing mortality (F = 5.1–6.9), so consequently a small component of the commercial catch consisted of males in larger instars. Size frequency analysis, which measured the percent exploitation of the μ = 156-mm CW instar, indicated that legal-sized males remained in relatively low abundance during this year-round fishery because of intense exploitation. Mark–recovery data and size frequency analysis also indicated this intense fishery was sustained throughout most of the year by a protracted moulting season. Consequently, we observed prolonged periods with a high percentage of less desirable soft-shelled males in the commercial catch.