Assessing the implications of live claw removal on Jonah crab (Cancer borealis), an emerging fishery in the Northwest Atlantic

Abstract

In the Northwest Atlantic fisheries management is adapting to emerging fisheries. The fishery for Jonah crab (Cancer borealis) is rapidly expanding resulting in a quadrupling of landings over the past 20 years. In response to this increased fishing effort, management plans have begun adopting a suite of regulatory measures, one of which allows the live removal of claws at-sea. The overall goal of this project was to determine if claw removal has an impact on crab mortality. Results from a series of laboratory trials with individual crabs (n = 240) indicate that double-claw removal incurs markedly more mortality (70 %) compared with single-claw removal (51 %). Mortality was significantly correlated with wound size, temperature, and shell condition (GLM, p < 0.05), as well as elevated levels of glucose and lactate in the haemolymph of declawed animals. We also conducted a comparative claw removal trial (n = 40) using both manual- and mechanically-induced (using a declawing tool) methods and showed that mortality in manually declawed crabs (87 %) was much higher than when claws were removed mechanically (40 %, Wilcoxon pairs test, p < 0.0001). Finally, when claws were removed from tagged crabs released in the field (n = 464), four times as many control crabs were recaptured than crabs with claws mechanically removed, and none of the crabs whose claws were manually removed were recaptured (p = 0.0048). Overall, claw removal results in a significant number of mortalities. However, our findings also provide a foundation for future investigations on the sub-lethal effects of claw removal on Jonah crabs as well as the impacts of claw harvesting to improve fisheries management of this rapidly burgeoning fishery.