Turtle Navigation

      Sea turtles are some of the oldest species on Earth. Their kind have been around for millions of years, and they have changed little over time.  They are the most gentlest of creatures and it is sad to know that they are on the endangered species list. They are also very unique creatures with some special talents.

      Green Sea Turtles are the most  common turtles in the US. Adult green turtles may reach a size of 1 m long and 180 kg mass. The carapace is smooth and is colored grey, green, brown and black. The plastron is yellowish white. Hatchlings weigh about 25 g, and are abo ut 50 mm long. Hatchlings are black on top and white on the bottom. Age at sexual maturity is estimated at 20-50 years.

     In the southeastern United States, green turtles are found around the U.S. Virgin Islands, Puerto Rico, and the continental U.S. from Texas to Massachusetts. Important feeding grounds in Florida include Indian River Lagoon, the Florida Keys, Florida Bay, Homosassa, Crystal River and Cedar Key. The primary nesting sites in U.S. Atlantic waters are along the east coast of Florida, with additional sites in the U.S. Virgin Islands and Puerto Rico.

     What makes these creatures unique is their navigation abilities. Birds, insects, and fish can use the orientation of Earth's magnetic field to navigate. But so far, we know of only one animal that can make a true map of Earth's oceans

     Every year female turtles come ashore to lay their eggs in a hole they dig in the sand. The baby turtles are on their own from the stars. After hatching, the turtles immediately crawl down the beach into the water. They set off on a journey through the North Atlantic gyre -- a large, circulating mass of warm water, within which food is plentiful. This current carries them in an enormous clockwise loop between North America and  Africa. Several years later, adult female turtles will find their way to the exact beaches where they were born -- where they will lay their own eggs.

     But how do they find their way back home? Drs. Kenneth Lohmann and
Catherine Lohmann, of the University of North Carolina at Chapel Hill believe that sea turtles can sense two properties of Earth's magnetic field -- its strength and the angle it makes with Earth's surface. The combination of these values varies around the world, providing turtles with a two-dimensional map - much like the maps we use to find our way on Earth.

    The Lohmanns placed two- and three-day old sea turtle hatchlings into pools and surrounded them with varying magnetic fields. Turtles subject to a magnetic field resembling that from the eastern side of the gyre paddled west .And turtles exposed to fields like those on the west side of the gyre paddled east. This inborn behavior may tell a sea turtle where she is -- and how to return home.