Fishery and Biological Characteristics of Jonah Crab (Cancer borealis) in Rhode Island Sound

Abstract

Jonah crab (Cancer borealis) is a demersal crustacean distributed throughout continental shelf waters from Newfoundland to Florida. The species supports a rapidly growing commercial fishery in southern New England, where landings of Jonah crab have increased more than six-fold since the early 1990s. However, management of the fishery has lagged its expansion; the first Fishery Management Plan for the species was published in 2015 and a stock assessment has not yet been created due to a lack of available data concerning the species’ life history and fishery. Fishing effort in the crab fishery is necessarily tied to fishing effort for American lobster (Homarus americanus), and the structure of this mixed crustacean fishery further complicates efforts to manage each of its component species. In the first manuscript of this thesis, a fishery-dependent sea sampling protocol was developed and implemented in Rhode Island Sound to (1) describe biological characteristics of the Jonah crab in Rhode Island Sound and (2) begin to characterize catch per unit effort in the Jonah crab fishery. With these methods, seasonal patterns in carapace width frequency and sex ratios were described for the commercial trap fishery, along with biological characteristics including shell disease condition, reproductive condition and allometric growth relationships. This study provides a unique description of commercial catch before discards and provides a more comprehensive description of the population than is available with dockside sampling methods. Conducting this type of data collection across the range of the species would substantially expand available data that is considered essential for constructing a stock assessment. The second manuscript describes growth characteristics of Jonah crab in Rhode Island Sound from data gathered during a laboratory study and via sea sampling in the commercial fishery. Description of the growth rates of exploited marine species is essential to understanding the impacts of fishing pressure on these resources and to predicting population abundances. Because crustaceans grow only during discrete molting events, description of growth per molt along with molting probabilities is necessary for estimating absolute growth rates of crustaceans. The results of this project provide characterization of growth per molt for male and female Jonah crabs along with description of molting seasonality for mature males. This thesis provides essential knowledge concerning growth, seasonal catch patterns and basic biological description of the Jonah crab to fishery managers charged with regulating the resource. To date, knowledge of the species has been limited enough to preclude the