Once in the water, hatchlings swim continuously for about two days. They try to reach open ocean as soon as possible because sharks and other predators are abundant in nearshore waters. So many hatchlings are eaten on their way to the open ocean that fewer than one percent are estimated to survive to sexual maturity. At first, they swim into the waves, which parallel the beach when close to shore. Farther from shore, however, wave direction no longer correlates with the direction of shore.
Biologists believe that hatchlings then switch to navigating using a biological magnetic compass.
Studies by Ken Lohmann of the University of North Carolina at Chapel Hill show that sea turtles can indeed detect and orient according to magnetic fields. Lohmann s work suggests that sea turtles can sense both the angle and intensity of the Earth s magnetic field, which vary depending on where you are on the surface of the planet. The angle of the magnetic field gives the latitude of a given position and the intensity gives the longitude. The second thing you need to know is where to go. We think hatchlings somehow record the latitude and longitude of their natal beach.