Diving behavior and thermal habitats of gravid hawksbill turtles at St. Croix, USA

Abstract

Knowledge of an animal’s behavior during particular life history stages can provide insights into habitat selection, and this can have important conservation implications. Gravid hawksbill turtles spend the internesting interval resting on the seafloor, but their diving behavior has only been previously examined in shallow-water habitats. We examined depth use of gravid hawksbills in a location of variable bathymetry to determine if hawksbills engage in deeper diving if deeper waters are available. We attached archival time-depth recorders onto hawksbills nesting at Sandy Point National Wildlife Refuge, St. Croix, US Virgin Islands, where the neritic zone ends within 500 m of the shoreline. We recorded seven internesting intervals from five individuals. Internesting intervals were characterized by long dives (mean 24.2 ± SD 22.3 min) to a constant depth, consistent with seafloor resting in a spatially restricted residence area. There was little variation in the water temperatures at all depths occupied (mean 29.06 ± SD 0.43 °C). Two turtles attained the deepest recorded dives for gravid hawksbills (95.1 and 84.4 m) and sometimes remained at depths greater than 60 m for up to 30 min. Although we recorded instances of relatively deep diving for the species, the overall pattern of seafloor resting and infrequent diving was consistent with hawksbills in other ocean basins with different offshore habitats. We propose that benthic resting is common behavior for gravid hawksbills globally, and protection of benthic habitats near the nesting beach should be a management priority