Slow and steady
Sea turtles return to Treasure Coast beaches to continue cycle of life
BY DONNA CRARY
Beginning in the spring and lasting through autumn, Mother Nature puts on an awe-inspiring spectacle along our coastline. Under dark, starry skies mother sea turtles emerge from the ocean so they can carry on their species. During this ancient ritual, the marine reptile slowly lumbers her way onto the beach to find a safe location to lay her eggs.
It is a difficult and delicate venture, where nesting conditions must be just right. If the setting is favorable, she meticulously builds her nest, lays her eggs, buries and disguises them with utmost care. Then she disappears back into the deep, not knowing if her young will survive.
The Treasure Coast is one of the leading hot spots for sea turtle nesting in the United States. Last year, around 26,382 nests were recorded. Seven species of sea turtles swim in the oceans today and three of those beach along our shores to lay their eggs.
Leatherbacks typically nest from early March until July. They are massive creatures usually weighing 800-1,000 pounds and are the only soft-shelled species of sea turtles. Loggerheads nest in April through September. They are the most numerous in our region and are the only ones that are not endangered. Green sea turtles usually arrive in May and nest through October.
When a female sea turtle is ready to lay her eggs, she returns to where she hatched many years before. She comes out of the ocean and carefully takes in all of her surroundings. While in water she glides gracefully; on land, she struggles awkwardly. She must drag her heavy body above the high tide line to find a suitable nesting spot. If she is not disturbed by artificial lighting, predators or humans, the turtle prepares a nest by digging a body pit with her front flippers. Then she digs a deeper egg chamber with her rear flippers, throwing sand methodically in all directions.
“The rear flippers are very dexterous, so basically she’ll scoop sand out with one flipper and kick it to the side, and the alternating flipper will do the same thing,” says Jeff Guertin, an environmental specialist with Inwater Research Group. “The depth of the egg chamber will depend on the species. Once the chamber is formed, the turtle will position itself over that hole and deposit the eggs.”
The number of eggs varies with the species. On average, loggerheads and green sea turtles lay 110 eggs, which are roughly the size of a ping pong ball. Leatherbacks lay 80 eggs in a nest and each egg is about the size of a billiard ball. Sea turtles can nest multiple times in one season.
After the turtle has laid her eggs, she fills the hole with sand making sure it is compact and completely covered. She camouflages her nest so that the eggs are safely hidden.
“The leatherbacks create a huge nest area,” explains Lauren Maline, a biologist with Ecological Associates. “Sand is thrown everywhere and they do an orientation circle and go back to the water. Green sea turtles have more of an organized mound and they make a huge secondary pit, where they have thrown sand behind them to cover their eggs. It’s a signature and it looks like a bomb went off at the beach. Loggerheads have the smallest and most organized nesting patterns. The incoming crawl is followed by a fluffy mound and a very shallow secondary body pit, compared to the green sea turtle.”
COOL DUDES, HOT CHICKS
Temperature plays a vital role in the biology of sea turtles. The sex of a sea turtle hatchling is determined by the temperature of its egg as it develops during incubation. Scientists call this phenomenon temperature dependent sex determination.
“Around 84 degrees Fahrenheit, a nest will produce 50 percent female and 50 percent male sea turtles,” Guertin points out. “If it’s cooler than that, you’ll be skewed toward males. If it’s higher than that, you’ll be skewed toward females. The moniker to remember is ‘cool dudes, hot chicks.’ ”
Temperature also determines the length of the eggs’ incubation period. Nests that are laid during the cooler months of spring will take longer to incubate than ones during the hotter months of summer.
The length of incubation varies with each species. Since they are the largest, leatherbacks have the longest period, which is around 60 to 75 days. The loggerheads and the green sea turtles incubate for about 50 to 60 days before they hatch.
LOOKING FOR SIGNS
During nesting season, scientists along the Treasure Coast daily survey the beaches and closely monitor for sea turtle activity. With a trained eye, they look for clues to piece together what happened on the beach the night before. The markings that sea turtles leave in the sand give them a good understanding of whether they successfully laid a nest or had a false crawl.
“Sometimes they have false nesting emergences,” says Quintin Bergman, an environmental specialist for Indian River County. “We get a lot of these instances when they hit a sea wall, beach furniture or other human disturbances. So they’ll come up and bump into something and turn around or see something there they don’t like and return to the ocean. That’s burning up a bit of their energy that they could be using to produce more eggs.”
The imprints that sea turtles leave in the sand resemble tire tracks. Area scientists can also identify the type of sea turtle by closely examining their particular markings.
“As turtles drag their body, they have different markings that they leave behind,” Bergman explains. “We know that loggerheads walk with one flipper, then the other. Green sea turtles walk with both flippers at the same time, like a breaststroke. They also have a bit of a longer tail, so they’re leaving another mark in the sand.”
When the embryo is fully developed and ready to hatch, it will use its egg tooth on its snout to hammer the egg open.
“When they break through and get out of the egg, they’ll start to straighten out and absorb some of the nutrients in their yolk sac,” Guertin explains.
“Over the next day or two, they will make their way to the surface. They’re climbing over one another and over the egg shells. And what that does is it gets the sand above them to trickle down, so they can slowly make their way to the surface.”
A nighttime trigger occurs where the cooling of sand causes them to rise to the surface. The boil of hatchlings pours from the nest as they make a mad dash to the water.
Baby turtles have little time to waste to reach the ocean. They rely on their senses of sight, smell, sound and touch to crawl to the surf.
“They look for the lowest, brightest horizon,” Bergman says. “They listen and smell for the ocean and they can also feel the ocean — the crashing waves — through the vibration of the sand.”
While they’re crawling their way to the water, they have to be on the lookout for predators such as ghost crabs, raccoons, birds and domestic animals. Artificial lighting is another big threat that can cause them to become disoriented.
“What we see a lot on our developed Florida beaches are disoriented nests,” Bergman adds. “The hatchlings come up and they walk in the wrong direction because of artificial lighting. They get stuck in the dunes; they spend more time on the beach; and they use up all of their energy. When disoriented, they’re more likely to get predated on by animals or they walk into a road.”
If a hatchling successfully makes it to the ocean, it continues to face many dangers to survive. It must avoid predators like birds and large fish that could easily consume it. Swimming through mountainous waves is no small feat for a tiny hatchling, as well. It must struggle to overcome and swim beyond the pounding surf.
After several attempts, the baby turtle goes into a swimming frenzy. Using the energy from its yolk sac, it swims until it reaches the sargassum weed line. Here it takes refuge finding food to eat and shelter from predators.
“They’re going to spend close to a decade maturing and foraging in that weed line,” Maline says. “We refer to this time period as the lost years because we don’t know a lot about that life stage. While they live in these sargassum patches, they drift with the ocean current. They are also feeding off of plankton and small fish. They’re in these patches until they reach juvenile size, about the size of a dinner plate. They migrate to more shallow, coastal areas, once they have grown to a size where they are less likely to be predated on.”
As they develop, sea turtles migrate for thousands of miles as they journey across the ocean to return home. They use the Earth’s geomagnetic field as an address system, as if they had their own built-in compass.
“Sea turtles are born pretty much with an understanding of magnetic fields,” Guertin says. “We don’t know 100 percent exactly how they’re doing this. We’ve seen that birds can migrate via magnetic fields and turtles can, too. It makes sense because they’re doing these trans-Atlantic journeys. They’re using the magnetic field of the Earth to navigate themselves.”
“That’s another reason why we should leave hatchlings alone on the beach,” Bergman advises. “We don’t know exactly when they are setting that home location. So somewhere when they’re developing to when they’re reaching the water, they are imprinting the beach of where it is. That way they know that this is home, and one day they’re going to return here to lay their eggs.”
Sea turtles become sexually mature between 15 and 30 years. When they are ready to mate, they journey along migration routes between feeding areas and nesting beaches. After their eggs have been fertilized, females return to their birthplace to nest, where a new life cycle miraculously begins.
Residents and visitors on the Treasure Coast have the opportunity to get up close and learn firsthand about sea turtle nesting. During the summer, a number of local organizations offer guided turtle walks at night to educate the public and build awareness about these fascinating creatures.
Registration for most walks begins on May 1 and can be accessed online.
If those who attend are lucky enough to witness a nesting turtle, they should make sure to stay with the guide at all times. Onlookers will be able to watch the turtle from behind, so as not to disturb the egg-laying process.
“Turtles don’t have great peripheral vision,” Maline says. “As long as we’re reasonably behind her, she won’t be able to see us. It’s really easy to see the eggs that way.”
No flashlights, cell phones or flash photography are allowed on the walks.
Some organizations also provide public excavation programs that are a daytime alternative to sea turtle walks. They are educational events where scientists dig up a turtle nest and inspect its contents, after the eggs have hatched. Every now and then, observers are pleasantly surprised to see a live hatchling wandering from the nest.
To promote a safe and successful nesting season, remember to keep the beaches dark, flat and clean. Turtles can be disoriented by artificial lighting. Help keep beaches flat by tearing down sandcastles and filling in holes, since nesting turtles and hatchlings can get stuck in those holes. And pick up trash and plastics and remove beach furniture, so they don’t obstruct the marine creatures.
Summer is the perfect season to kick back, relax, and have a good time on our south Florida beaches. If you encounter a nesting sea turtle while on the beach at night, stand out of the way, and let nature take its course.
“Respect it at a distance, not using any flash or light,” Bergman says. “Observe it and enjoy it — it is a phenomenal creature that people on our coast get an opportunity to see.”
Sea Turtle Walks
Organizations permitted by the Florida Fish & Wildlife Conservation Commission to conduct sea turtle walks:
- Archie Carr National Wildlife Refuge
- Sebastian Inlet State Park
- Disney Beach Resort at Vero Beach
- Florida Power & Light Company
- Inwater Research Group Inc.
- Ecological Associates Inc.
- Environmental Studies Center
- Florida Oceanographic Society
- Hobe Sound Nature Center