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Amazing Science

By Mary Pringle for The Island Eye News

A cutaway model of a loggerhead nest hatching made by Barbara Bergwerf.

The use of DNA analysis has not only made a huge difference in forensics and crime solving, but also in sea turtle research and conservation. In the 12 years since 2010, the Turtle Team has been collecting an empty egg shell from each nest on our two islands. 

By analyzing the DNA from these, scientists can identify individual female loggerheads. 

This information tells us how many clutches of eggs she lays each year, if she is nesting on more than one beach, which years she is breeding and more. In earlier times, turtles were tagged, and then it was hoped that they might be seen again, but this was not likely. 

Some interesting examples of things we have learned from this study have been: 

• In the early years of this study we were told that a loggerhead nested on the Isle of Palms. Then two weeks later she nested on Hatteras Island in North Carolina and then laid her third nest on Cumberland Island, Georgia. So they do not necessarily come back to the same area where they were hatched as we had thought before. 

• A mother turtle who nests on Cape Island near McClellanville has 12 daughters who are nesting and in addition four granddaughters also nesting now. This is remarkable because it takes these turtles up to 30 years to mature and begin breeding. That means this grandmother turtle is probably close to 100 years old and still laying eggs! 

• Another turtle who has nested on Sullivan’s has nested on 14 different beaches in North Carolina, South Carolina and Georgia. She also laid a record seven nests in one season in 2018. 

When a nesting female mates in the spring, she can then fertilize all of the possible four to six nests that she will lay that year. 

As egg follicles move down her oviduct where they receive shells for her next clutch, a few of her cells are scraped away and trapped between the layers of the inner membranes of her egg shells which can later be studied to identify her. So this is all maternal DNA and only mothers, sisters, daughters, nieces and granddaughters can be identified, with no male turtles in this study. We have learned that some turtles wander to multiple states while others nest only in Wild Dunes or another specific area. 

In the 2021 season we have seen some of our old friends, turtles that we have had nesting here since 2010 the first year of the genetics research project such as: 

1. Loggerhead No. 2,992 who has laid 28 nests since 2011, always in odd years (skipping the even ones to build up her strength and produce about 600 eggs in a season). 

She seems to love the solitude of Dewees Inlet at the very north end of the IOP where she nested regularly every two weeks, laying approximately 140 eggs every time. 

What an amazing girl she is. We soon learned when to expect her back and she did not disappoint us. However, one time she fooled us and laid near 5th Avenue instead. 

2. Loggerhead No. 9,206 on Sullivan’s Island has always chosen to lay eggs between Station 14 and Station 18 and nowhere else. She nested in 2016, 2019 and then again in 2021. She usually lays small clutches of 60-80 eggs and we know she has laid three nests there this season and possibly two more. We are waiting for those results to be read. If so, that means she laid five of the 13 Sullivan’s Island nests this year. 

3. Loggerhead No. 14,013 is nesting for the very first time and laid once on Sullivan’s and twice more on IOP this season. Loggerhead No. 14,038 has nested twice in Wild Dunes and is another young female who has never laid eggs before this year. 

It is particularly rewarding for us to see these new or “neophyte” nesters who are coming ashore in 2021 for the very first time to lay eggs. Scientists are cautiously optimistic that the previous population decline has turned around with nest numbers now increasing. We feel special affection for these young females and imagine that just maybe they could be the same hatchlings that we helped survive in the early years of the Island Turtle Team. It takes them decades to mature and the odds are against them because statistically even with nest protection only one in one thousand will survive to adulthood. 

We have been told that before groups like ours began to relocate eggs and protect nests from predators, the survival rate was one in 10,000. That makes our work all worthwhile. 

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