Date of Award

Spring 2025

Project Type

Thesis

Program or Major

Marine Biology

Degree Name

Master of Science

First Advisor

Nathan B Furey

Second Advisor

Elizabeth A Fairchild

Third Advisor

Jason S Goldstein

Abstract

AbstractJonah crabs (Cancer borealis) are an economically and ecologically valuable fishery species found in the Northwest Atlantic Ocean. As fishing pressure on Jonah crabs in US waters grows, catch-per-unit-effort (CPUE) has declined in recent years. The notable decline in CPUE seen in the US Jonah crab fishery indicates that alternative fishery practices, such as claw-only harvesting, should be further investigated to determine the potential utility in improving the health and sustainability of this evolving fishery. Claw harvesting, one potential relief to fishing mortality, may offer a decrease in crab mortality but is also affected by removal technique as well as the indirect, sublethal impacts of modified behaviors (e.g., foraging, mating, competition). In this thesis, I used a high-resolution acoustic telemetry positioning system to track the movements of 50 tagged Jonah crabs (30 in 2018 and 20 in 2019) in the Piscataqua River (Portsmouth, NH, USA) and quantified their movements from October 10th -December 5th, 2018 over 57 days and July 2nd - November 14th, 2019 over 136 days. I used Hidden Markov models to quantify and assess in situ fine-scale movements and infer three behavioral states of tagged Jonah crabs: slow-movement (e.g., resting, burrowing, or feeding in place), active movement (e.g., potentially foraging), and displacement (e.g., quick directed movement). In association with this study, a single claw was mechanically removed from half of the tagged males released in this study (10 in 2018 and 6 in 2019) to investigate the sublethal effects of claw removal on movement and associated behaviors. Environmental data were also collected to investigate potential abiotic predictors of Jonah crab movement and behaviors. Using these fine-scale telemetry data, I calculated an average movement rate for Jonah crabs of 67 (range of 45-88) meters per hour, similar to recent findings for other related decapod species. Temperature was retained as a significant predictor in the top generalized linear mixed models for Jonah crab movement rates, and results indicated a negative relationship for temperature and movement rate in both years; it is unclear if these increased movement rates are associated with pre-overwintering behavior. There was no evidence of substantial or obvious impact on movement or associated behaviors on tagged Jonah crabs with a single claw removed, indicating that mechanical single-claw harvesting may be a useful management strategy to consider in the future management of this fishery.

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