Project Title: Continued Monitoring of Florida’s Main Adult Green Turtle Foraging Site
Project Manager: Ryan Welsh
Organization: Inwater Research Group (Non-Profit Organization)
Grant Amount: $18,426.25
Completion Date: 2019-02-12
Summary: In the course of ongoing work in the Key West National Wildlife Refuge, Inwater Research Group (IRG) has identified areas adjacent to the refuge near the Marquesas Keys containing foraging sub-adult and non-nesting adult green turtles. This area, known as The Quicksands, is the only published foraging grounds for green turtles of these size classes in the southeastern United States. IRG has been returning to these grounds annually to perform vessel-based transects and capture-mark-recapture activities since its discovery in 2005, creating a decade-long monitoring database. Distance sampling analyses have shown that densities of these size classes on this foraging ground are among the highest in the world. Tag returns of captured animals have established connectivity to nesting beaches in the Caribbean Basin, and recapture data provides evidence of long term residency on the foraging grounds. IRG considers these foraging grounds to be regionally important and has committed to continuing long term monitoring in this area. IRG will return to this remarkable green turtle foraging ground in 2017 for 10 days to continue the following activities: collect and analyze data on size frequencies, sex ratios, and prevalence of disease; perform fixed repeatable surveys to determine density and abundance of turtles observed on the foraging grounds; collect samples from captured green turtles for genetic and stable isotope analysis.
Results: During this project we conducted 76.4 km of visual transects in the Marquesas region of the Key West National Wildlife Refuge, including 36 kilometers of our fixed grid west of the Marquesas Keys. We observed 88 green turtles (25 adults, 62 sub-adults and 1 juvenile) and 2 adult Loggerheads. The Sighting Per Unit Effort (SPUE) for our standardized transect was 0.4 turtles per transect kilometer. Analysis of this transect data through the population modelling Program Distance indicates that the 30 km2 foraging grounds had approximately 4967 green turtles present, or 165 turtles per km2. The ratio of subadults to adults was approximately 75:25, with 3638 (121 turtles per km2) subadults and 1329 (44 turtles per km2) adults being estimated in the area. We also performed 40.4 km of HUNTs (Haphazard Unmarked Nonlinear Transects). During these HUNTs we observed 41 Green turtles (33 Subadults and 8 Adults) and 4 Loggerheads (2 Adults and 2 Subadults). We captured a total of 12 sea turtles during these sampling trips, including 9 green turtles, 2 loggerheads and 1 hawksbill. All turtles were measured, tagged and photographed before release and blood/tissue samples were collected for genetics, sex determination and stable isotopes. All samples have been sent to their respective labs (Dr. Brian Shamblin, Dr. Roldan Valverde and Dr. Simona Ceriani), where we are still awaiting results. A majority of our capture effort focused on the foraging grounds west of the Marquesas Keys where we captured a total of 9 large green turtles that ranged from 68.5 – 97.8 cm straight carapace length (SCL, mean=83.7, SD=11.4). Of the green turtles captured on the foraging grounds 3 were females, 2 were males and 4 were sub-adults with undetermined gender. Captures in the refuge also included 2 loggerheads ranging from 63.7 – 81.3 cm SCL (mean=72.5, SD=6.5) and one hawksbill (23.9 cm SCL).