Is the seagrass greener on the other side? Faster growth in Biscayne Bay, Florida’s nurse sharks (Ginglymostoma cirratum) compared to neighboring conspecifics of Bimini, The Bahamas

Abstract

Effective management of vulnerable species requires a precise understanding of life history. In 2024, Fadool et al. published the first von Bertalanffy growth model for the nurse shark ( Ginglymostoma cirratum ), reporting an asymptotic maximum length L ∞ of 303.28 cm and a growth coefficient k of 0.04 yr −1 for the population in Bimini, The Bahamas. We investigated whether nurse shark growth varies in nearby Biscayne Bay, Florida, an adjacent site within the western Atlantic region. We used 37 recaptured nurse sharks from Biscayne Bay to generate a comparable growth model, which estimated a significantly smaller L ∞ of 259.26 cm and a larger k of 0.11 yr −1 than Bimini. Biscayne Bay’s empirical growth rates were significantly higher on average than Bimini and exhibited a significantly steep decrease with increasing shark size not observed in Bimini. Additionally, the minimum linear displacement of 48 recaptured sharks was positively correlated with shark size, suggesting potential site fidelity to a small home range (1.6 ± 2.2 km) that increases with age. Our results indicate that differences in growth can occur over relatively small spatial scales despite environmental and geographic similarities, potentially reflecting genetic differences driven by historic fishing pressure or differences in resource availability. Significant growth rate variation between adjacent shark subpopulations assumed to be ecologically indistinct highlights the importance of sampling across a region’s subpopulations to inform management with more accurate life history data.

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