Date of Award
2024
Degree Type
Thesis
Degree Name
Master of Science in Oceanography
Specialization
Biological Oceanography
Department
Oceanography
First Advisor
Kelton McMahon
Abstract
In southern New England, rapid ocean warming over the past two decades has caused substantial redistributions of fishes, invertebrates, and the fisheries they support. The rapid emergence of the warm water-tolerant Jonah crab (Cancer borealis) fishery, once discarded as bycatch from the now declining lobster fishery, illustrates a prime example of climate-adaptive shifts in southern New England fisheries. However, limited data exist on the basic life history of Jonah crab, despite their growing economic and societal value. This lack of knowledge hinders ocean management capacity to meet multiple ecological, economic, and socio-cultural goals of sustainable harvest. Off the southern coast of Rhode Island, Jonah crab are currently harvested in two fishing zones (inshore: fishing zone 539 within 3 NM of shore and offshore: fishing zone 537 ~80 NM SSE from Newport, RI), which are holdovers from the lobster management zones. Jonah crab landed in the offshore fishing zone are significantly larger, on average, than those landed in the inshore fishing zone, setting up the Ontogenetic Migration hypothesis, i.e., that the cause of this size differential is due to ontogenetic migration of crabs from inshore to offshore. We test this hypothesis using an isotopic clock approach to examine the movement ecology of Jonah crab between isotopically distinct inshore (n = 59 crabs) and offshore (n = 64 crabs) fishing zones across a broad size spectrum (70-153 mm). To do this, we established the existence of distinct isotope signals for residence in inshore and offshore fishing zones, validated with regional particulate organic matter isoscapes (geospatial isotope maps), which revealed distinct geospatial gradients in environmental stable isotope values between inshore and offshore. We then used stable isotope analysis of two Jonah crab tissues with different metabolic turnover times: the carapace (reflecting residence at the time of the last molt, > one year ago for nearly all crab in this study) and muscle (reflecting residence at the time of collection, integrated over the last 1.5-2 months) to construct an “isotopic clock” of residence throughout the regional isoscapes. We did not see isotopic evidence of population-wide ontogenetic migration in Jonah crab between inshore and offshore fishing zones, as there was no clear trend in the isotope values in Jonah crab carapace with size for crab caught in the inshore or offshore fishing zones. However, there was isotopic evidence to suggest an ecologically relevant proportion (~25%) of the Jonah crab collected from the offshore fishing zone migrated there after past residence in the inshore fishing zone. This work provides key data on critical life history characteristics around movement ecology and migration capacity needed to understand the connectivity of Jonah crab in southern New England.
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This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License
Recommended Citation
Agvent, Lindsay, "TESTING THE ONTOGENETIC MIGRATION HYPOTHESIS IN THE EMERGING RHODE ISLAND JONAH CRAB (CANCER BOREALIS) FISHERY USING STABLE ISOTOPE ANALYSIS" (2024). Open Access Master's Theses. Paper 2520.
https://digitalcommons.uri.edu/theses/2520