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Environment: DNA tests will help sea turtle census
By Jackie R. Broach
The S.C. Department of Natural Resources is the newest participant in a multi-state genetics research project that will answer questions about sea turtle nesting habits and provide a census of nesting females.
By collecting a DNA sample from every nest recorded on state beaches, the project will allow researchers to identify individual nesting females and gather 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.
But, the most important piece of information the study aims to provide has to do with sea turtle population, said DuBose Griffin, who heads the state’s Marine Turtle Conservation Program.
The question of how many nesting sea turtles are out there is one marine wildlife officers have long wanted an answer to. But the travel habits of sea turtles have made it impossible to get any realistic kind of count.
“You’re dealing with a marine animal that has a very large geographic range,” Griffin said. “When they leave these beaches, they go as far north as Delaware Bay and as far south as the Bahamas and the Florida Keys.”
With a way to accurately measure sea turtle populations, officials will be able to start assessing changes to those numbers, Griffin added.
All seven sea turtle species are listed under the federal Endangered Species Act.
Researchers have used flipper-tagging studies in the past to try to answer questions about sea turtle populations and nesting, but it is estimated the studies fail to intercept 10-20 percent of nesting females. A high rate of tag loss is also a problem.
S.C. United Turtle Enthusiasts, a group that monitors and collects data on nesting activity in Georgetown and Horry counties for natural resources officials, measures turtle crawl widths and looks for distinctive crawl marks in an effort to identify repeat nesters on area beaches, said Jeff McClary, a founder and head of the group.
But the genetic program will provide much more reliable data.
While biologists know sea turtles nest in two- or three-year cycles, laying several nests in a season, the project will tell researchers exactly how many nests each turtle lays and where they lay them.
“Until now, all we were able to do was guess,” McClary said. “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. This will be definitive. It will actually put a name or a face on all our turtles.”
The genetics recovery project started two years ago in Georgia and has already identified about 1,200 individual sea turtles and 20 mother-daughter pairs.
North Carolina is also a partner in the program.
Griffin said the information about the mother-daughter pairs is of particular interest, as it will help create an understanding of how precisely a daughter returns to the site where she hatched to lay her own eggs.
It takes about 30 years for sea turtles to reach reproductive age. They mate at sea and return to the beach where they hatched to nest.
DNA collection will be performed by volunteers with McClary’s group. Beginning this month, the start of sea turtle nesting season in South Carolina, volunteers patrol beaches in the mornings looking for signs of sea turtle activity. When a new nest is located, they rope it off to keep it from being disturbed by beach-goers and cover it with a silk screen to protect it from predators.
Their duties this year will also include collecting one egg from each new nest to gather DNA from.
Maternal nuclear DNA contained between layers of the inner shell membrane are needed for the study.
In most nests an egg will have to be torn open to get the necessary material, McClary said. If a nest has to be relocated, which volunteers do for nests laid in dangerous areas where they might be trampled or washed out, 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.
The DNA samples will be sent to the University of Georgia for “genetic fingerprinting.”
Griffin said the project wouldn’t be possible without the help of volunteers who were willing to take on the task of collecting DNA in addition to their usual duties.
The state’s participation in the project has received grant funding for three years, but Griffin said she hopes the project can continue well beyond that.
To keep track of nesting activity in Georgetown and Horry counties, visit SCUTE’s page on Facebook. Keep up with nesting activity statewide or worldwide at seaturtle.org/nestdb.