Sublethal behavioral and physiological effects of claw removal on Jonah crabs (Cancer borealis)

Abstract

Jonah crabs (Cancer borealis) have been caught as incidental bycatch for over 80 years, but in recent years they have become a targeted fishery, especially in Southern New England where the American lobster (Homarus americanus) population has declined, and harvesters have begun seeking alternative fisheries. This shift has prompted the need for more biological data for Jonah crabs so that this expanding fishery can be managed more effectively. For example, in some areas of its range males have both of their claws removed at sea and only the claws are landed; however, little is known about what happens to the crabs that survive this practice. The focus of this study was to evaluate the impacts of claw removal on Jonah crab mating success, feeding ability and locomotion. In mating trials, all males, regardless of claw status, managed to successfully mate with females that molted while they were paired together (clawed n = 4, claws removed n = 8). When Jonah crab activity was measured in the laboratory, crabs with intact claws were significantly more active than crabs with both claws removed (clawed: 25.0 ± 8.0% of each hour active, 1 claw removed: 18.1 ± 7.3% of each hour active, clawless: 13.6 ± 9.04% of each hour active, mean ± SD). Similarly, based on data from a tag/recapture experiment, crabs with both claws missing moved about half the distance per day as control crabs, between the time they were released and first recaptured (clawed: 117 ± 43.1 m/day, clawless: 50 ± 11.3 m/day, mean ± SE), although the difference was not significant. These changes in locomotion could be the result of the blood loss associated with claw removal. We found that hemocyanin levels dropped significantly after the removal of both claws and remained so for up to two weeks. Finally, crabs with no claws were able to feed, but they had difficulty opening mussel shells, which might influence their diet in their natural habitat. These data suggest that those Jonah crabs that do survive the claw removal process might be impaired, but should be able to forage, mate, and help sustain the population.