National Geographic : 1994 Feb
I try to be gentle as possible," says Ernest Carlisle, cooling a soft-skinned leather back found ina trap net off Rhode Island. Unlike shrimp trawls (below), traps let tur tles rise for air. Carlisle cut an old hook from this 700-pounder and set her free. When a loggerhead hatchling-or any hatchling-breaks through the sand after 50 to 70 days, how does it know where to go? It was once thought that it headed toward the sea only because the water is brighter than the shore. But experiments by Mike Salmon indi cate that it is also crawling away from the land's higher horizon. Salmon also discovered, along with Jean ette Wyneken of Florida Atlantic and Ken Lohmann of the University of North Carolina, that once in the water hatchlings orient them selves in the direction from which the waves are coming. They are also guided by another biological compass--an inborn sense of mag netic direction.* From Florida beaches the hatchlings swim about 25 miles in 30 hours to take shelter and feed in sargassum, a bushy floating seaweed. Currents draw them farther out, where many are picked up by the Gulf Stream and carried across the Atlantic. The next time anybody sees these little loggerheads, they are at least four inches long and living near the Azores. That internal compass and sense of wave direction presumably help the loggerheads find their way back across the Atlantic and guide the other species on their migrations as well. Folklore has held that turtles return to nest on the beach where they hatched. Now genetic evidence suggests that it is true. The DNA in a cell nucleus is from both *See "Secrets of Animal Navigation," by Michael E. Long, NATIONAL GEOGRAPHIC, June 1991.