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The incredible egg: Tracking sea turtles through DNA

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Data collected from a decade of sea turtle nests now sheds light on the larger population 

Mary Sheridan and Lauren Connolly are hunched over a tablet computer at 5:30 a.m., willing it to connect to the internet. Unfortunately, their powers are overwhelmed by the winds of the previous night’s hurricane, which grazed the beach and knocked out the Wi-Fi.

Their mission was to scout the beach of Hilton Head Island in their pick-up truck and identify new loggerhead turtle clutches of eggs laid overnight. They also planned to check nests close to the end of their incubation period.

But with the tenuous connection to GPS, that may have to wait.

“We start checking them at 45 days,” says Sheridan, pointing to the small dots on the glowing map in front of her “Our main job of finding nests we can do. But unfortunately, since we have no way to figure out which nest is more than 45 days old, we don’t know which is which.”

Nevertheless, they begin their slow crawl of the beach, scanning the sand for the digging-dragging marks from female loggerheads. Sheridan and Connolly are volunteers with the island’s Sea Turtle Patrol, which is part of a network of staff and trained volunteers who fan out across beaches from North Carolina to northern Florida between April and October. They mark locations of new nests, log them into a database, monitor their progress and extract one egg from the dozens that are laid.

The shell of that egg will go on to become part of one of the world’s largest marine turtle databases, housed at the Warnell School of Forestry and Natural Resources at the University of Georgia. Up and down the beaches, one shell from each nest is placed in a vial, marked with the location, date and unique identifying number, and sent to a lab at Warnell. Once there, its DNA is extracted and logged into the Northern Recovery Unit Genetic Capture-Recapture database at

The project began 15 years ago by recently retired Warnell professor Joe Nairn, and today it keeps track of more than 13,000 female loggerhead turtles nesting along the East Coast. The project is unique in the amount and type of information it tracks—by logging DNA of female turtles, it provides a more accurate and long-term picture of the population.

“Everybody around the world, with sea turtles, they count nests because that’s the easiest thing to do. But, since these females can lay multiple clutches of nests, does more nests mean more females? Or is it changing conditions out on the foraging grounds?” says Brian Shamblin, who took over the loggerhead DNA project in 2019. He has been instrumental in the project since its start. “We’ve demonstrated there’s a strong correlation between nest numbers and the number of females—but it’s tricky.”

Tricky, says Shamblin, because 15 years of data is just barely enough to start revealing trends. In general, populations are on the rise—changes in fishing regulations 20 years ago are revealing their benefits, as more turtles reach sexual maturity than in previous generations. But the data is also revealing new puzzles.

“Our work is showing, yes, there’s a lot of females out there. But we seem to be seeing higher population turnover than we ever thought was possible,” he says. “We don’t know what’s driving that pattern, but every year 30% to 40% of the females we see are new. It’s good from a recruitment standpoint, but then a portion of those females never come back. So, until we get a better handle on what’s driving those patterns, I don’t know that we can say, ‘Oh, it’s fine.’”


When Shamblin came to Warnell more than a decade ago, he planned to study jungle birds in Indonesia. But the country’s regulations about transporting samples made the project impossible. “And I approached Brian and said, ‘Would you be interested in working on sea turtles?’” says Nairn. Neither had experience with the species, but both were interested in how genetics could be used for conservation.

“When it started, we were talking about doing a few nests on a beach somewhere; I never envisioned doing the whole Georgia, South Carolina and North Carolina coast,” he adds with a laugh. The first couple of years focused on loggerhead egg samples collected in Georgia, but once officials in North and South Carolina learned about the project, they were interested in helping it expand. “They all saw this project as something that would be really new, and would give us new information, so everyone was on board.”

Mark Dodd, coordinator of Georgia Department of Natural Resources’ sea turtle program, saw the genetics component as the perfect complement to a sea turtle monitoring project begun in the 1960s by UGA ecology prof

essor Jim Richardson. Georgia DNR eventually took over the project and expanded it from Little Cumberland Island to all of Georgia’s beaches in 1989.
The data collected from that project gave us the first insights into the loggerhead population. Because it takes female loggerheads about 30 years to reach sexual maturity, long-term data sets are essential for understanding larger population trends. But sea turtles don’t lay eggs every year, which means tracking nest numbers only tells one part of the story.

“But it’s important to know if the number of nests is declining because females are nesting less frequently. So, the genetic information is critical just in establishing the number of nests and nesting females,” says Dodd. “But secondly, are they nesting less frequently or taking fewer years between nests? We were able to start answering those questions with the genetics project.”

And now, the combined information from the DNA samples and the nesting data is coming together to give biologists a missing piece to their management puzzle: population statistics.

Working as part of the Georgia Cooperative Fish and Wildlife Unit, Warnell alumnus Bryan Nuse (PHD ’14) recently developed a tool to predict female loggerhead abundance and nest abundance. Georgia DNR is now testing the model, which helps to better understand threats to the sea turtle population—such as the effect dredging off the coast of Savannah may have.

It’s a tool that would not have been possible without the long-term data sets from the DNA project and the nest monitoring, says Clint Moore, Co-Op Unit leader.

“For the first time, our model integrates the data streams from both projects, which strengthens our understanding of sea turtle population dynamics beyond what each dataset alone could provide, and it permits us to make population projections into the future,” says Moore. “More broadly, the model could be used to predict how the population would respond to threats, such as loss of beach habitat, or conservation actions, such as increasing the protection of nests.” 

The model gives professionals such as Dodd a road map for the future.

“As someone who’s responsible for managing the population without a model, all you can do is try to minimize the sources of mortality and try to minimize those threats as much as possible,” he says. “It’s nice to have a model, and it wouldn’t be possible without the genetic project and long-term nesting data.”


This is the kind of information that Doug Hoffman has been looking for.

Hoffman (MS ’90) is a wildlife biologist for the National Parks Service and has been stationed on Cumberland Island since 2006. Loggerhead monitoring is a major part of his schedule, as turtles begin to show up a little earlier and lay eggs later in the season than on other beaches. Some turtles come every three years and some return every other year, because typically loggerheads return to the same stretch of beach time and again.

In 2009, Hoffman began sending eggs to the Northern Recovery Unit DNA project. While Cumberland Island and Little Cumberland Island have sea turtle data that goes back decades, the detail that biologists could extract from the DNA added a new level of understanding, he says.

“You’re able to look at females we sampled in 2009 and we can tell the frequency between nest cycles and also if those turtles have a high site fidelity—does she lay one or two nests and then go to Ossabaw Island?” says Hoffman. “So, you can pull a lot of data from just pulling that egg out of a nest.”
From the mid-1970s to 2009, Cumberland Island averaged about 200 nests a year. But since around 2010, that number has tripled, topping out at about 650 to 700 nests each year. This increase aligns with the implementation of turtle excluder devices, or TEDs, in commercial fishing in 1987—allowing many more turtles to reach sexual maturity and now nest on beaches decades later.

Long-term data sets are essential to evaluate policy changes like the use of TEDs. But with 20% to 30% of nests coming from new, unsampled turtles each year, understanding the larger population is still a puzzle for Hoffman. The new model now in development by Georgia DNR can hopefully offer some management options in the future.

“Every year you get a certain sample of turtles that we never sampled before. So the question is, are those newly maturing adult females, or are those coming from somewhere else?” says Hoffman. “But on the flipside of that, every year we’re not seeing a percentage of turtles we’re expecting to resample. What happened to those turtles?”

The data are also important for education and outreach to the public. Every year, thousands of visitors pass through the Georgia Sea Turtle Center, which has been part of the Northern Recovery Unit DNA project from the start. It’s also one of two places in Georgia doing nighttime tagging of turtles and collection of turtle mother DNA.

In this way, the Sea Turtle Center connects visitors to turtles who frequent Jekyll Island’s beaches. People learn about how conservation helps and how they can make changes in their own lives to help turtles and other animals.

“We have this great opportunity to not only contribute mother DNA and eggshell DNA, but also to engage with visitors on the beach through nighttime programming,” says Nicole Thomas (BSFR ’10, MNR ’12), education program manager at the center. “So, we use the program as a launching point to engage with the research we’re doing and how we’re using this information to better understand sea turtles and their conservation needs.”

The Sea Turtle Center takes information gathered about the turtles that nest there—often, they see the same turtles again and again—and creates stories about the animals that appear on Jekyll’s beaches. For example, Junebug is a turtle who regularly nests on Jekyll, and the center shares her journey through nest monitoring and tracking her DNA. 

It’s a way to make an abstract concept more real. When people can better identify with an animal, they can also understand the issues they face and potential solutions.

“It gives us an opportunity, when we combine science with an emotional connection, to help change behaviors,” adds Thomas. “We’re trying to teach people how we can be turtle friendly, and we can do that in a way that supports wildlife conservation.”


The volunteers with Hilton Head’s Sea Turtle Patrol also do their share of outreach and education as part of their morning route. As Sheridan and Connolly make their way along the shore, small groups of vacationers wander over to see what’s happening.

They patiently explain the tracks, how they look for a nest, why they pull an egg out, why they mark the location with a post, how far folks need to stay away and what to do if someone sees a turtle or a nest. Before leaving, they tape off an area around the nest and then drive a few circles to help cover the tracks. 

It’s much different on Cumberland Island, where Hoffman’s interns encounter more wild horses than tourists. But for both—and on beaches hundreds of miles away—the collected eggs in their vials are boxed for Shamblin’s pick-up.

Throughout the summer and into the fall, Shamblin makes the rounds. He brings back thousands of samples, persevering through pandemic restrictions and equipment shortages (test tubes, in particular, can be difficult to come by during the age of COVID-19). 

“When the pandemic hit, I had plenty of concerns about what was going to happen to sampling—when you’ve been sampling for over 10 years and you miss a year, you’re done,” says Nairn. “But I will say this, Brian got it done. He battled the elements all summer. ... And it takes a lot of effort to get this project done; we’re covering thousands of miles of coastlines every day.”

Once back at the lab, a small but dedicated group of lab workers begin the process of extracting DNA. For the past decade, the DNA project has been carried by a small army of mostly undergraduate student workers who conduct the tests, log the DNA and keep samples organized from year to year.

The students are critical to the project’s success, says Nairn and Shamblin. Working under one or two professionals, up to a dozen students each year get hands-on research experience that gives them an edge after graduation. Incorporating undergraduate research assistants was a major goal of the program from the start, adds Nairn, and many have gone on to graduate school or have taken positions in natural resource conservation.

In addition to overseeing a lab and connecting with networks of volunteers and getting samples back for testing, Shamblin is also responsible for funding.
But, Shamblin and Nairn say, state agencies see the value in the project, as well as the potential for the future. It’s a set of data that nobody else in the world has, and with a decade of data under their belt, they’re only just getting started.

“The goal is to better understand what’s happening out there,” adds Shamblin. “Our work is showing that yes, there are a lot of females out there, but we seem to be seeing a higher population turnover than we ever thought was possible. We don’t know what’s driving that pattern, so continuing to look at it is important.”

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