National Park Service


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Understanding the spatial ecology of highly mobile marine vertebrates is necessary for informing conservation and management strategies aimed at protecting such species. Buck Island Reef National Monument (BIRNM), off the coast of St. Croix, US Virgin Islands, harbors critical foraging habitat for Critically Endangered juvenile hawksbills Eretmochelys imbricata that exhibit high site fidelity until sexual maturation. Using an array of fixed passive acoustic receivers that covered over 20.2 km2 at its largest configuration and in-water biannual sampling, we analyzed residency patterns and habitat use of 29 hawksbills. High recapture rates allowed for long- term data collection for some individuals, with 1 individual being detected within the array 1952 d (mean ± SD: 411 ± 444 d). We used detection data to construct a resource selection function based on a generalized linear mixed model in order to determine relative habitat selection, or the use of different habitat types within an area proportional to the ‘true’ selection. Our covariates in the model were benthic structure, bathymetry, time of day, and year. Results showed selection by tagged individuals for shallow (<20 m) depths in areas with high rugosity characterized by a high density of reef or rock. However, individuals also selected areas comprised primarily of sand interspersed with seagrass pastures. We also used the best supported model to predict relative selection across BIRNM and found that the total area of high relative selection decreased significantly at night. The information provided will help guide both future in-water surveys for cryptic hawksbills and management decisions about public area-use at BIRNM.