Window on Nature
By Lowell & Kaye Christie, F47246
We may never see a loggerhead sea turtle in the wild. Even so, it’s nice to know they’re still out there cruising the coastal waters after 150 million years.
The name “loggerhead” comes from the turtle’s large head (10 inches wide in an adult) and the powerful jaws it uses to crush crabs, mollusks, and other bottom-dwelling crustaceans attached to reefs and rocks. Add that to a reddish-brown carapace (top shell) that stretches three to four feet in length, and an adult turtle’s weight of 200 to 350 pounds is not surprising.
Loggerheads begin life small enough to fit in your hand; consequently, it takes quite a bit of food for a hatchling to grow that big. Fortunately, they aren’t picky eaters, consuming conchs, crabs, horseshoe crabs, shrimps, sea urchins, squid, octopuses, whelks, and the occasional jellyfish. It certainly must maintain a healthful diet to live 50 years or more.
An estimated 14,000 female loggerheads nest in the southeastern United States annually “” approximately 35 to 40 percent of the world population. State by state, 91 percent of the total U.S. contingent hatches in Florida, 6.5 percent in South Carolina, 1.5 percent in Georgia, and 1 percent in North Carolina. Loggerheads live along the Pacific coast of the United States also, but extensive turtle tagging proved that they hatched in Japan.
Loggerhead life isn’t without its hazards. Despite their status as a threatened species, the turtles are still caught by nets used in shrimp fishing and gill netting. Offshore oil and gas exploration and production holds even more potential for disaster. One big oil spill, and ….
Finally, there’s the ongoing problem of habitat destruction. When pristine beaches are graded and developed, it might be good for humans, but it’s certainly bad for turtles.
As their name implies, loggerhead sea turtles live almost entirely in the open ocean. They begin reaching sexual maturity at 25 years of age. After they breed, the females hit the beach to lay their eggs.
In the southeastern United States, females begin nesting at varying times, from late April all the way to early September. Nesting activity is at its peak in June and July.
And how do they find a good nesting beach, after migrating so many miles and spending all those years in the open ocean? As far as scientists can tell, the hatchlings are imprinted with their natal location as they leave the nests and head for the water. Scientists believe the turtles’ journey to the ocean imprints the magnetic field of the earth on their brains. This gives them a sense of direction, and allows them to return to their natal area when they mature in many years later.
A gravid female crawls up on the beach at night to locate just the right place to make her large nest. She digs out the sand deep enough to hold a clutch of 120 to 150 eggs about the size of Ping-Pong balls. When finished, she conceals the eggs by kicking loose sand all over the nest. Then, her responsibilities met, she makes her way back to the ocean. She’ll return to repeat the process twice more during the season. That done, she spends the next two to six years in the ocean before breeding again.
It takes 53 to 55 days for loggerhead eggs to incubate in Florida, and 63 to 68 days in Georgia. Clearly, the time it takes for eggs to hatch is inversely related to temperature. As with all sea turtles, the babies’ gender also depends upon the temperature. Females result from cooler temperatures, and males from warmer temperatures.
Turtles hatch in the evening, when fewer predators are around. Cooler sand temperatures signal this event. With no one around to stand guard, the hatchlings must travel across the beach to the water’s edge on their own.
The hatchlings determine which way to go based upon the light reflected off the surf. That’s why it’s so important to observe warnings calling for “Lights Out for Sea Turtles!” Lights on the beach or along the shoreline can confuse the hatchlings and lead them in the wrong direction.
Loggerhead turtles are most vulnerable right after they hatch, for predators seem to have an uncanny knack of knowing when this will happen. On their trip from the nest to the deep ocean water, they are at risk from birds, crabs, and fish.
Once in the ocean, hatchlings swim continuously for up to 24 hours to reach the Gulf Stream. There, they drift with the current in the sargassum weed, where they are protected and have plenty of food for sustenance and growth. Scientists are not exactly certain how long they remain in the shelter of the sargassum weeds. Eventually the turtles strike out on their own into the ocean. After a period of 20 to 25 years, the survivors (possibly as few as one in 10,000) will gather off the coast to mate and nest.