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Environment: DNA study alters view of sea turtle nesting habits
By Jackie Broach
Research on sea turtles has always indicated that loggerheads return to the same beaches time after time, year after year to nest.
It’s called site fidelity, but a multi-state genetics research project that started last year has found that female loggerheads travel much farther between nesting sites than was believed.
The data shows one female last year nested at Cape Hatteras, N.C., on July 1, Pawleys Island on July 18 and Bull Island on Aug. 2.
A turtle that laid the only nest at Litchfield Beach last year, on June 13, first nested at Edisto Beach, which is south of Charleston in Colleton County, about three weeks earlier. After Litchfield Beach, she nested at Pawleys Island on June 21 and then went back to Edisto Beach, where she laid a fourth nest on July 15.
“That’s 41 days and four beaches. She covered a lot of territory,” said Phil Schneider, a volunteer coordinator for S.C. United Turtle Enthusiasts, a group that monitors and collects data on nesting activity in Georgetown and Horry counties for the state Department of Natural Resources.
He suspects that turtle nested somewhere else between Pawleys Island and her second stop at Edisto, but the nest either wasn’t found or hasn’t yet been matched to that turtle.
The project tracks nesting turtles through DNA samples collected from every nest recorded on beaches in South Carolina, North Carolina and Georgia.
The goal is to provide a census of nesting females, including information about how many nests a female lays in a single season, how frequently she nests, whether she nests on more than one beach and how many turtles nest in more than one state.
“Until now, all we were able to do was guess,” said Jeff McClary, founder and head of SCUTE. “If we had two nests in the same area laid a couple of weeks apart and they had similar crawl widths, we’d figure it was probably the same turtle.”
There were 3,400 DNA samples collected from nests last year and only about one-third have been analyzed so far, so more results will be coming in throughout the year.
Sampling will continue this year when turtles start nesting again in May.
While some turtles put more space between nesting sites, others do tend to stick to a smaller area, according to data from the project.
Of 17 nests recorded on Pawleys Island and Litchfield Beach last year, DNA information has been received on nine turtles, Schneider said. Four nested at both Pawleys Island and either DeBordieu or Hobcaw beaches.
SCUTE volunteers will continue to collect DNA samples on Georgetown and Horry County beaches. Beginning next month, volunteers will start patrolling beaches in the mornings looking for signs of turtle activity. When a new nest is located, they rope it off to keep it from being disturbed by beachgoers and cover it with a net to protect it from predators.
DNA is collected from one egg in each nest.
In most nests an egg must be opened to get the necessary material, McClary said. If a nest has to be relocated, which volunteers do for nests laid in areas where they might be trampled or washed away, volunteers will likely be able to use an egg with a casing that is already torn.
Every nest usually has at least a few eggs that are damaged as they drop into the chamber during the laying process, but those eggs are usually located in the center of the nest, so volunteers won’t be able to reach them without digging up the nest.
Volunteers can’t wait until the nests hatch, because DNA needs to be collected within 24 hours of an egg being laid; before male DNA starts to combine with female DNA as the egg develops, McClary said.
DNA samples are sent to the University of Georgia for “genetic fingerprinting.”
For more information about the project, visit the project website