Grant: 20-022R
Project Title: Movement Patterns and Life History Parameters of Low Nesting Year Green Turtles (Chelonia mydas) in the Gulf of Mexico
Project Manager: Kristen Mazzarella
Organization: Mote Marine Laboratory (Non-Profit Organization)
Grant Amount: $21,174.00
Completion Date: 2021-06-09
Summary: Green turtles were first documented nesting in southwest Florida in 1992 and nest statewide in a biennial, sawtooth pattern; nesting in high numbers one year followed by much lower numbers the next year. To date, ten nesting green turtles have been satellite tagged on Casey Key, Sarasota County, FL. Satellite telemetry data suggested that foraging grounds differed geographically for green turtles nesting in low-nest years versus those nesting in high-nest years. However, sample size in low-nest years is small (n=2), preventing robust analysis between years. Our goal is to increase the sample size of nesting green turtles tracked during low-nest years to determine whether differences between the foraging areas do exist between low-nest and high-nest years. We will deploy satellite tags on green turtles in 2020, adding new data to existing low-nest year data. We will compare these data to our findings from high-nest years. Satellite data provided by the tags will expand our knowledge of green turtle migration on the west coast of Florida. We will identify life history parameters such as clutch frequency, inter-nesting areas, nest site fidelity and home range at foraging grounds. GPS location data will be used to identify crawls such that nesting data - nest placement, clutch size, incubation period and reproductive success - can be collected for each turtle. In addition, samples will be collected for collaborators studying genetics and stable isotopes such that a comprehensive life history will be available for each satellite tagged turtle. This information will contribute to our understanding of lesser-studied Gulf nesting green turtles, as well as identify whether differences exist between turtles nesting in high and low nest density years.
Results: (1) Monitor Casey Key tagging beach for nesting green turtles between May 15, 2020 - Aug 1, 2020. Regular nighttime tagging patrols were conducted May 21 - July 27, 2020, when nesting dropped off considerably. A total of 572 turtle encounters were documented comprised of 349 individuals (206 neophytes and 143 remigrants), 15 green turtles and 334 loggerheads. Two new turtle corrals were created from treated plywood, cut into 4 boards, with hand-cut slots and handles, and coated with a zero-VOC exterior wood sealer. Boards were strapped to the ATV during night surveys and utilized for corralling green turtles for satellite tagging. A night vision scope was purchased for identifying the status of the turtle in the nesting process at a distance, rather than approaching the turtle. It was also helpful in showing the turtle and nesting process to the public who approached while staff were waiting to approach the turtle. Anecdotally, this may have reduced the amount of time that the public were around the turtle (many left before taggers approached the turtle) and set a good example of watching from a distance
without the use of red lights. Battery life and distance was adequate for use by taggers but improvements of both would be warranted.
(2) Deploy satellite tags on and track up to three nesting green turtles during the 2020 nesting season. Satellite tags were deployed on three green turtles consisting of two neophytes and one one-year (2019) remigrant. One neophyte transmitted for 58 days and the other for 145 days. The remigrant was tracked for 27 days until her tag was lost. She was observed without a tag, nesting on Manasota Key on 21 July, four days after her tag's last transmission. She was identified by her flipper and PIT tags and inspection of her carapace indicated that the tag and associated epoxy had been cleanly removed.
(3) Identify the distance from nesting beach to the inter-nesting area used by satellite tagged green turtles tracked in 2020. Using QGIS (QGIS.org, v2.8.3) and R (R Core Team, 2021, v4.0.4), data points were separated into nesting and inter-nesting states by individual and mean coordinates by day were calculated. The resulting coordinates were combined distance was measured from each point to the nearest shoreline. During the inter-nesting period, turtles were 286.6m - 7.8 km (mean = 2.1 km, median 2.6 km) from shore. The core inter-nesting area was calculated from the mean daily coordinates and the centroid of the 50% KDE polygon was measured to the nearest shoreline,
resulting in a distance of 2.0km.
(4) Identify the inter-nesting interval of satellite tagged green turtles in 2020 based on satellite telemetry and tag/recapture data. The three turtles were satellite tagged on their first encounter on the tagging beach. Each turtle laid 3-4 nests. Nest were identified using the GPS quality locations and haulout times delivered by the satellite tag and ground-truthed by morning nest surveys. Inter-nesting intervals
ranged from 9 - 14 days with a median of 10 days.