Date of Award

2024

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Fisheries, Animal and Veterinary Science

First Advisor

Austin Humphries

Abstract

The blue crab (Callinectes sapidus) is an emblematic species for much of the mid-Atlantic and Gulf coasts, supporting vital fisheries in these areas. Evidence has shown that many species, including blue crabs, are undergoing northward shifting distributions. This has resulted in speculation about an increasing blue crab population and its capability to support a viable fishery in Rhode Island (USA) coastal waters. Currently, the blue crab is an unassessed species in Rhode Island, and few studies have focused on their population dynamics in the northeast region.

In the first manuscript of this thesis, a Bayesian hierarchical modeling method was employed to leverage data from several fisheries independent monitoring surveys and estimate a state-wide index of blue crab relative abundance from 1970-2022. Life-history traits were characterized, including size-at-maturity (L50) and the relationship between carapace width and length. Size-at-maturity was smaller than reported in most other studies (101 mm for males and 111 mm for females) but was still within the range of estimates for females reported in the Chesapeake Bay region. The length-weight relationships were similar to those reported in other regions, but not significantly different between males and females. This study provides critical elements for assessing the Rhode Island blue crab population, provides advice for prospective data-limited stock assessment methods, and discusses future research needs to further build upon these methods.

In the second manuscript, a winter dredge survey targeting blue crabs was employed to further fill gaps in blue crab data not possible with existing monitoring work. Abundance and distribution data on blue crabs were analyzed to understand spatial patterns by sex or maturity stage. In addition, the effects of environmental variables and sampling location on density and presence/absence was investigated. This research indicated the dredge survey was effective at sampling blue crabs during the winter when the species is dormant. Recommendations on survey design refinement, including survey stratification and additions to allow for estimating winter mortality, are provided to assist the survey in being a valuable long-term monitoring tool.

The work presented in this thesis provides essential information on blue crab population dynamics in Rhode Island coastal waters, including trends in their abundance, spatial distribution, and important life-history characteristics. These results represent continued progress in providing data for a stock assessment of Rhode Island blue crabs in support of a successful management program.

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