Infrared photo taken in the dark of loggerhead hatchlings emerging from their nest through a protective screen (Credit: Barbara Bergwerf)
Many things have to be just right for loggerhead sea turtles to survive. The sex of these turtles is determined not by X and Y chromosomes as in mammals, but instead by the temperature during the middle weeks of incubation of their eggs. The pivotal temperature is approximately 85 degrees Fahrenheit. If it is above this in the nest, the results will be more female turtles. Below it, there will be more males. Each tiny loggerhead sea turtle begins its life when it uses a sharp "eye tooth" to cut its way out of the soft leathery egg that has incubated for about two months and is buried about 12-20 inches down in the warm sand on the beach. After several days, each hatchling and over 100 siblings dig their way together, moving up toward the surface. When their little shells have straightened out and they are just under the sand, they wait until they sense the temperature has cooled—a signal that night has come and the beach is dark and free of most predators.
As if someone has thrown an "on" switch, they suddenly become very active, emerging from the nest together and making a race downhill toward the ocean. At this stage, they look for the brightest light they can see and instinctively run toward it. If they are lucky, they see the moon or starlight and the white waves of the surf. If there are other lights visible, they go that way. Their main beach predator is the ghost crab, which may grab a few as they scramble to the water.
Once they reach the surf, they know to swim against the waves, beginning a years-long, solitary journey. Once they are farther out, they can navigate the Earth’s magnetic field with tiny crystals in their brains. During the three-day "swimming frenzy," they are able to swim continuously until they reach the Gulf Stream because they are nourished by the yolk sac remnants in their bodies with no need to find food. If they make it to the Gulf Stream, they can rest in the huge floating beds of Sargassum weed, where they find shelter and many small creatures to eat. It is said that most of them do not survive the first dangerous 24 hours of life, but because so many eggs are being laid, hatching, and tiny turtles coming out this time of year, the population, which was formerly in decline, is making a slow recovery.
The next life stage of a young loggerhead is floating in the Atlantic gyre, a circular current that carries them near Europe and finally back to the North American coast, where they arrive as teenagers to forage and grow to adult size. It takes 25 or 30 years for them to reach maturity when the females begin to nest on the beach.
Nesting Update: As of July 17, the Island Turtle Team has found and protected 54 nests on the Isle of Palms and three on Sullivan’s Island. These began to hatch on the night of July 12. Beach patrol usually ends on August 15, which marks the normal end of the nesting season. It takes until October for all of these nests to finish hatching.