Grant: 18-016R
Project Title: Comparing demographics on Florida's only adult green turtle foraging grounds during high and low nesting years
Project Manager: Ryan Welsh
Organization: Inwater Research Group (Non-Profit Organization)
Grant Amount: $15,400.00
Completion Date: 2020-02-28
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. IRG considers these foraging grounds to be regionally important and has committed to continuing long term monitoring in this area. In 2017, a record green turtle nesting year for the state of Florida, IRG surveyed these foraging grounds during. During these surveys IRG found a ratio of adult to sub adult green turtles (25:75), to be quite different from the 40:60 ratio normally observed on these foraging grounds. Given the biennial patterns of Florida nesting green turtles, 2018 is forecasted to likely be a low nesting year. IRG will return to this remarkable green turtle foraging ground around the same time as in 2018 for five days to collect the data and compare these efforts to our 2017 findings. We will collect and analyze data on size frequencies, sex ratios, and prevalence of disease, perform fixed repeatable transect surveys to determine density and abundance of turtles observed on the foraging grounds, and collect samples from captured green turtles for genetic and stable isotope analysis.
Results: The primary purpose of this trip was to perform these standardized grids nearly a year apart from each other to compare how numbers of foraging adult and subadult turtles were compared to the biennial nesting patterns exhibited by Green Turtles on Florida’s Atlantic beaches. By comparing 2017 to 2018, we can see that 2018 saw an increase in numbers of both subadult and adult green turtles. While both size classes saw an increase in numbers, the ratio of subadults to adults decreased from, 75:25 to 65:35. Indicating that proportionately more adult turtles were found on the foraging grounds during the low 2018 green turtle nesting season then during the high 2017 green turtle nesting season. While subadults have always outnumber adults on this foraging ground, the addition of more adults to the area was an expected outcome, but still of great interest. This information is relevant, as the connection of Florida’s nesting beach population to this foraging ground is still anecdotal. While mark-capture-recapture work on this foraging ground over the years has indicated that turtles that nest in Mexico and Costa Rica contribute more than Florida nesting turtles. Seeing a direct change in the makeup of the foraging population corresponding with the nesting patterns seen on Florida’s beaches provides better evidence of connectivity between the two. However, future trips should be planned to occur around this time in the future to continue to see if this pattern still holds. We captured a total of 10 sea turtles during the August 2018 sampling trip, including seven green turtles and three loggerheads. All turtles were measured, tagged and photographed before release and blood/tissue samples were collected for genetics, sex determination and stable isotopes. A majority of our capture effort focused on the foraging grounds west of the Marquesas Keys where we captured a total of 7 large green turtles that ranged from 48.4 – 100.6 cm straight carapace length (SCL, mean=77.5, SD=12.8). Of the green turtles captured on the foraging grounds 4 were females and 4 were sub-adults or juveniles with undetermined gender. Captures in the refuge also included three loggerheads ranging from 75.4 – 81.9 cm SCL (mean=78.1, SD=5.6). Of the loggerheads captures two were subadults of indeterminate gender, while one was an adult female carrying tags from the Casey Key nesting beach in Sarasota County, Florida. Correspondence with Mote Marine Lab indicated that this turtle had been seen nesting once in 2006 and twice more in 2015, before being seen on the foraging grounds of the Key West National Wildlife Refuge by us in 2018. Recent stable isotope analysis revealed similar trends that we have found with previous years stable isotope work in the KWNWR. Which is that the isotopic niche of the green turtle and loggerheads overlapped. No differences in d13C and d15N between loggerheads and green turtles, which was surprising. Differently from other studies, we found no relationship between body size and d15N values for either species. Both species showed a wide range of nitrogen values suggesting plasticity in diet among individual, something that deserves further investigation. Genetic results were obtained from the 11 green turtles, 2 loggerheads and a single hawksbill captured. The two loggerheads were found to be of the haplotypes A1.1 and A2.1, which is from Florida and Florida or Mexico respectively. Of the 8 green turtles analyzed, 3 were found to be of haplotype A3.1 (Which is an amalgamation of Costa Rica/Florida/Cuba/Mexico), 4 were found to be of haplotype A1.1 (Which consists of turtle likely from the Tamaulipas/Veracruz areas of Mexico or Florida) and one that was found to be of haplotype A22.1 (which consists of turtles from Quintana Roo, Mexico), interestingly this turtle had a flipper tag that indicated previous nesting in Mexico, however as of the grant report we have yet to hear back from either Mexico or the Archie Carr Center for Sea Turtle Research about the original tagging information of this animal.