Identifying Habitat Associations of Sea Turtles within an Area of Offshore Sub-Tropical Reefs (NW Atlantic)

We observed sea turtles with time-lapse video cameras (deployed for studies of fish behavior during June 2017) at “live-bottom” reefs in depths of 18–20 m within Gray's Reef National Marine Sanctuary off the coast of Georgia, USA (NW Atlantic). These reefs, sandstone ledges emerging from surrounding sand seafloor, were deeply undercut and apparently served as resting habitat for turtles to wedge themselves between sand seafloor and hard rock overhead. We observed 22 distinct individuals over 27 occurrences including 10 Caretta caretta (L.) (Loggerhead), 3 Chelonia mydas (L.) (Green Sea Turtle), and 9 unidentified to species based on individual markings. We documented resting periods up to 144 minutes (mean = 37.2 min, SD = 39.1). Notable was that most observations (67%) occurred during twilight and night periods. To put these video observations in perspective, we analyzed diver observations of 34 turtles encountered at the surface prior to and during visual fish census surveys (2010–2017) at 18 ledges. Those ledges had significantly taller and deeper undercuts than 18 other ledges with no turtles (ANOSIM P = 0.043 and SIMPER comparisons). These limited observations indicate time-lapse video of seafloor habitats along with diver surveys may yield new insights into sea turtles' habitat requirements, patterns of site fidelity, and ecological role as ecosystem engineers, as well as effects on sea turtles of coincident human uses such as fishing, vessel use, and recreational diving.