These majestic sea creatures come to our shores every year to lay eggs before vanishing back into the deep. But how much do we really know about them?
Story by Barry Kaufman
Ours are unique
You might think that when it comes to sea turtles, they are pretty much the same all over. These are, after all, animals that travel far and wide when they are not returning to shore to nest. However, years of genetic testing have shown that the sea turtles arriving on our shores are fundamentally different from populations elsewhere, like the Florida Panhandle or the Yucatan.
In addition to genetic markers, there are physical differences that separate a South Carolina turtle. “Ours are bigger and have a higher domed shell,” said Sally Murphy, creator of South Carolina’s sea turtle program.
Their eggs are a top priority
There are numerous reasons why a mother coming ashore to make a nest should be left alone. She has traveled hundreds of miles to the region where she was hatched and is ready to lay lots and lots of eggs.
“When they build up enough fat stores, they know they can nest again. They’re not feeding during migration, and not feeding during the nesting season,” said Murphy. “They have a rigid shell and it’s just too full of developing eggs. There’s not enough room in there for a full stomach.”
Hence, the two to three years that a female must have between re-nestings. Burning through your body fat while laying up to 500 eggs a season will take it out of anyone.
You’ll know the tracks when you see them
Loggerheads are not the only animals enjoying our beaches. Beyond tourists, there are numerous sea birds, raccoons, crabs and the occasional alligator that traverse the sand during all hours of the day. As such, there are a slew of different tracks. But turtle tracks stand out, because they are gigantic.
“People will send me a picture of a track maybe a foot wide, saying, ‘A sea turtle nested last night,’” said Amber Kuehn, head of Sea Turtle Patrol Hilton Head Island. “Their track is going to be two to three feet wide and you’re going to notice it. Most people don’t understand how big a sea turtle is.”
They aren’t as loyal as you think…
There’s a common misconception that turtles will return each year to the beach where they were hatched. While they certainly can “sense” what general region they are in based on a magnetic signature within the Earth’s magnetic field, they often don’t return to the same exact spot where they were born.
“This whole business about turtles coming back to the beach where they were born is a romantic myth,” said Murphy. “They may switch beaches even within the same nesting season.” In fact, our distinct population of sea turtles can create nests in upwards of five different spots per season within the general boundaries of Georgia, South Carolina and North Carolina.
… Except for Myrtle
While sea turtles tend to be pretty variable about which beach they choose, there’s at least one sea turtle with a special affinity for Hilton Head.
“We have a turtle who nests on Hilton Head, and she lays up to eight nests in a season,” said Kuehn. “Myrtle,” as she is called, is tracked by her unique genetic identifier and has laid hundreds of eggs on our island. Sea Turtle Patrol HHI even erected a sculpture and put up a plaque honoring Myrtle, before an unruly group of visitors took a hammer to it.
Artist Mira Scott painted a second Myrtle statue, with all of her Hilton Head Island hatchlings depicted crawling up her shell toward the moon in a dark sky. The original sculpture will be donated to the Sandbox Children’s Museum opening in the new Celebration Park. There will be a new sculpture presented each year.
You really, really shouldn’t dig deep holes
One of the biggest battles won in recent years to protect sea turtles is the Town of Hilton Head Island’s ban on digging holes deeper than one foot with the additional requirement that it be filled in before leaving the beach. Not only do these craters potentially trap hatchlings as they make their way to the water, they are also a hazard to beachgoers who may stumble upon them on a night time beach walk.
“With good intentions, some people dig trenches from the nest to the surf, hoping to direct the path of the hatchlings toward the water as they emerge, and what that does is create a funnel for water into the nest as the tide comes in,” said Kuehn. “They drown. Water can go over a nest as long as it passes over and trickles down. In heavy rain or king tide, that’s when it fills, and we’ll lose a nest.”
The future is female
Recent studies into sea turtle nests have discovered some astonishing new information that could have huge ramifications for the future of the species. Around day 40 (during the middle trimester of incubation), the embryos will begin to differentiate their gender. If the temperature stays above 95 degrees consistently, the nest will overheat and fail. And if the temperature happens to be above 82.4 degrees throughout the nest at that pivotal 40-day mark, the whole nest will become female. Cooler nests produce males.
And that fine-grained sand on the south end? It’s great for drainage, but not as good at insulation, resulting in a slightly higher incubation temperature. The initial results of a three-year, SCDNR permitted study conducted by Kuehn, reveals that the five nests equipped with temperature loggers in 2019 were female biased despite sand type.
“Fine sand incubates at a higher temperature,” said Kuehn. “We are trying to find where on our beach is most successful for incubation and sex ratios. In the future, it is possible that we’ll have to adjust where we put nests or try to cool them based on directives from SCDNR. You have to have males.”
Due to natural erosion, the tides affect each beach differently. As a result, nest proximity to the water can change, allowing the tides to inundate them.
“Sea turtles don’t know high tide versus low tide. Whenever eggs are ready to be laid, they have to release them,” said Kuehn. If that time coincides with a low tide, they have a long, labored walk to reach the dry sand. It would be so convenient for them to be able to pick high tide for a short walk to their nest site. (There is some evidence that they do this on Georgia beaches.) And because sea turtles will lay when they encounter warm, dry sand, irrespective of the variable tides, they could wind up creating their nest well below the spring high tide on full or new moons, the highest tides of the month. Add in rising waters from the change in sea level, and you have particularly bad conditions at the north and south ends of the island.
We know which ones keep coming back
When a new nest is discovered, Sea Turtle Patrol staff will retrieve a single egg. The egg shell is transferred into a vial labeled with a nest number, which is sent to Dr. Brian Shamblin’s lab at the University of Georgia for genetic testing. From there, scientists can analyze the DNA to track the eggs to a specific individual female, not to mention that female’s forebears.
“Over the years with all these samples coming in, they have now tracked grandmothers, mothers and daughters,” said Murphy. In several cases, scientists have documented two grandmother sea turtles that still return to South Carolina beaches to nest. “Which means they’re at least 90 years old,” added Murphy.