Growth and molting characteristics of Jonah crab (Cancer borealis) in Rhode Island Sound

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The Jonah crab, Cancer borealis, supports a rapidly growing commercial fishery in southern New England. However, a lack of data concerning its life history, including growth dynamics, hinders the creation of a thorough stock assessment for the species. In this study, the incremental growth and seasonality of molting in Jonah crabs from Rhode Island Sound was examined in specimens collected from commercial traps and monitored in flow-through seawater tanks. Regression analysis from molt increments of 119 female and 91 male crabs indicated growth dimorphism in mature Jonah crabs, with diverging trends in proportional growth with size between the sexes at the sizes observed. Molting seasonality and size-dependent molt probabilities in male Jonah crabs were studied via periodic sampling and observation of male specimens in a laboratory setting across a range of 10-mm carapace width size bins throughout a year-long period. Laboratory results were corroborated by seasonal patterns in shell disease and molting conditions recorded while sampling at sea in Rhode Island Sound during commercial fishing operations. A discrete molting season was identified in June for male Jonah crabs smaller than 120 mm. Molting probability decreased with increasing carapace width and males larger than 120 mm did not molt during the year-long study, suggesting that growth is slow and molting events are rare for C. borealis at larger sizes in this region, or that there are ontogenetic migrations in the species and molting occurring outside the study region. Results presented here provide fundamental growth information for C. borealis with direct implications for management of the Rhode Island Sound fishery.

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Fisheries Research