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Abstract Understanding how aquatic animals select and partition resources provides relevant information about community dynamics that can be used to help manage conservation efforts. The critically endangered hawksbill sea turtle ( Eretmochelys imbricata ) spends an extended part of its juvenile development in coastal waters. A strong proclivity to remain resident in small areas, often in high density, raises questions about how juveniles partition resources including selection of habitat and spatial overlap among conspecifics. Using between 36 and 41 acoustic receivers in the 1.5 km 2 study site, this study quantified day-and-night habitat selection, as well as 2D and 3D space use of 23 juvenile hawksbills within two adjacent Caribbean foraging grounds—Brewers Bay and Hawksbill Cove, St. Thomas, US Virgin Islands—between 2015 and 2018. We found that coral reef, rock, and the artificial dolosse forming an airport runway, were the most strongly selected habitats based on resource selection indices. Individual activity spaces in 2D and 3D were both larger during the day compared to night, although the same parts of the bay were used by each individual during both periods. The 3D approach also showed deeper space use during the day. Weekly comparisons of activity space between individuals showed limited overlap (mean 95% UD overlap; day: 0.15 (2D) and 0.07 (3D), night: 0.11 (2D) and 0.03 (3D)), suggesting some degree of resource partitioning or territoriality. Results from this study provide relevant space use information for resource management of juvenile hawksbills, in which many populations are facing habitat degradation and population declines. 

Space-use by aquatic ectotherms is closely linked to environmental factors such as temperature due to thermal-mediated metabolism and energy requirements. These factors are important, as they may alter an animal’s exposure to food/predators, hinder physiological function, increase competitive interactions, or even prompt population or biodiversity loss. Using general linear mixed-effects models, we investigated the influence of medium-term (months-years) environmental (diel period, water temperature, season, wind speed, air pressure, habitat type) and biological (turtle size) variation on space-use metrics for the Critically Endangered hawksbill sea turtle Eretmochelys imbricata , including dive duration, activity space, and rate of movement. We tracked 17 resident juveniles between August 2015 and May 2018 with a compact acoustic telemetry array (35-41 receivers in ~1 km 2 ) in Brewers Bay, US Virgin Islands. Diel differences in space-use were significant and highlighted periods of relative inactivity (e.g. resting) during the night and activity (e.g. foraging) during the day. Water temperature was also an important covariate influencing behavior leading to shorter dive durations and higher rates of movement in warmer temperatures. High contribution of random effects (individual and year) to model variation was also apparent, suggesting that juvenile hawksbills can operate outside the relatively narrow environmental range experienced within the study area. Nevertheless, ongoing climate trends (e.g. warmer temperatures and more extreme weather events) pose a significant concern for hawksbill populations, as juveniles spend their developmental period in shallow nearshore areas where environmental impacts will likely be greatest.