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SCCF provides update on night-time turtle tagging project

By Staff | Oct 9, 2019

PHOTO PROVIDED Jeff Book measures the carapace of a nesting loggerhead turtle. Red filters were distributed to beach-goers to keep flashlights from disorienting sea turtles.

The Sea Turtle Program’s tagging project was launched in 2016 to learn more about the turtles that use our beach to lay their eggs. A typical night for our team involves patrolling the beach from sunset to sunrise in search of nesting females. When a turtle is encountered she is scanned for existing tags, tagged if none are found, and measured with calipers and a measuring tape.

Since the project’s inception, our team has documented 1,178 encounters with turtles on the beach at night, representing 587 unique individuals. Having this information allows us to ask questions such as: What is the spatial distribution of nests for an individual female? What will nesting look like in the future, taking into account possible changes to our nesting beach? When a sea turtle comes onto the beach and doesn’t lay eggs (a “non-nesting attempt”), where and when does the turtle come back to lay her eggs? How many nests and eggs does a single female lay in one season, and how much does hatch success vary among her nests?

Of the 587 individuals we’ve seen, 236 have been encountered more than once. An interesting fact about sea turtles is that they don’t nest every year – each individual lays approximately 3-6 nests over the course of the season and then spends a year or two foraging to replenish her energy reserves before returning to the nesting beach. The number of years between nesting events is termed the “remigration interval.” The 2019 season, which marks the fourth year of the tagging project, was the first year we were able to take a good look at these data. Our average remigration interval is 2.2 years, with 36 of our resighted turtles nesting every other year, 13 turtles nesting every third year, and two turtles nesting in 2016, 2018 and 2019.

To calculate an accurate remigration interval we will also correct for tag loss rates, capture probability, and survival on our beaches. We ultimately hope to estimate the number of turtles that use Sanibel as nesting grounds.

Highlights of the 2019 tagging season include:

– A new record of 353 documented turtle encounters from May 1 to July 31

– Six green sea turtles were seen on Sanibel this season (Dellora, Andrea, Kate, Holly, Jane and Melanie), totaling 18 observed nests

– The average loggerhead carapace size was 94.5 centimeters (slightly over 3 feet), with our largest loggerhead measuring in at 115 centimeters (almost 4 feet long)

– Staff interacted with 1,126 beach-goers at night to educate them about the impacts of flashlights on sea turtles

Kelly Sloan is a biologist and the sea turtle coordinator for the Sanibel-Captiva Conservation Foundation’s Sea Turtle Program.