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Population Structure and Size at Maturity of the Caribbean Spider Crab, Maguimithrax spinosissimus, around Eleuthera, The Bahamas

Logan R. Zeinert1,2,*, Ami Adams2, Meghan Burchell3, Nathan J. Robinson2,4, and Iain J. McGaw1,2

1Department of Ocean Sciences, 0 Marine Lab Road, Memorial University, St. John’s, NL A1C 5S7, Canada. 2Cape Eleuthera Institute, Cape Eleuthera Island School, Eleuthera, The Bahamas. 3Department of Archaeology, 310 Prince Philip Drive, Memorial University, St. John’s, NL A1C 5S7, Canada. 4Institut de Ciències del Mar, Spanish National Research Council (CSIC), Barcelona, Spain. *Corresponding author.

Caribbean Naturalist, No. 91 (2023)

Abstract
Maguimithrax spinosissimus (Caribbean Spider Crab) is the largest crab in the Western Atlantic, reaching 3 kg in weight and 170 mm carapace width (CW). There are currently no commercial fisheries for M. spinosissimus; however, its large size and relative abundance could make this species a potential candidate for an artisanal fishery. Here, we investigated the sizes of crabs across various habitats in Eleuthera, The Bahamas, including patch reefs, a blue hole, and an anchialine pond. We collected a total of 392 individuals, of which 42.1% were males. Males were larger than females with a mean CW of 107.7 ± 18.6 (SD) vs. 94.3 ± 13.6 mm. Using principal component analysis and hierarchical cluster analyses, we determined that morphological maturity was reached at 96.2 mm and 72.3 mm CW in males and females, respectively. In contrast, males and females reached behavioural maturity at 80.1 and 72.1 mm CW, respectively. We also attempted to use the gastric mills to determine the age of crabs by sectioning the ossicles and looking for seasonal growth rings; however, this did not yield any conclusive findings. We assessed the meat yield of male and female crabs to ascertain their suitability for a fishery. The meat yield relative to their wet mass was 14.1 ± 1.1% for males and 10.9 ± 0.7% for females, which is comparable to other decapods. Overall, M. spinosissimus were locally abundant, but not widespread. We suggest that an all-male harvest with a minimum landing size of 110 mm carapace width would allow male crabs to mature (and breed), while providing full protection for egg-bearing females. Furthermore, limiting collection to free-diving only could ensure a sustainable artisanal harvest in the Bahamian archipelago.

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