Notes: Possible Consequences of Intensive Fishing for Males on the Mating Opportunities of Dungeness Crabs

Abstract

The trap fishery for Dungeness crabs Cancer magister in British Columbia is regulated by a minimum legal size limit of about 154 mm notch-to-notch carapace width (CW). This effectively bars females from the catch in most regional fisheries because few females attain this size. Consequently, in heavily exploited populations, males greater than the minimum legal size are rare and the sex ratio of adults favors females. As is typical of cancrid crabs, female Dungeness crabs mate with males considerably larger than themselves. In light of this and of data we present on male mating activity, sizes of mating pairs, and the degree of exploitation of males, we propose that females greater than about 140 mm CW would have difficulty finding a sexual partner in intensively exploited fisheries. Fewer matings of larger females could result in lost egg production, which suggests to us that increased understanding of the effects of a male-only fishery on the dynamics of Dungeness crab reproduction is important for confident management.