How sea turtles navigate across vast expanses of featureless ocean to reach feeding and breeding sites has long been a mystery. Now, clues are surfacing to indicate turtles rely partly upon invisible landmarks created by the Earth’s magnetic field.

The turtles were placed into cloth harnesses and tethered to limit their travel.

July 30, 2004

How turtles navigate across vast expanses of seemingly featureless ocean to reach distant feeding and breeding sites has long been a mystery of the seas. Now, clues are surfacing to indicate sea turtles rely at least partly upon an invisible map of landmarks created by the Earth's magnetic field.

While technological global positioning systems process signals from satellites, the turtles' system draws upon variations in Earth's magnetic field, which give each geographic area a distinctive magnetic pattern. New research shows that sea turtles can apparently detect and distinguish among the magnetic fields in different locations, enabling them to compile a "magnetic map" for navigating to specific feeding and nesting areas.

The findings, reported in the April 29, 2004, issue of Nature, may enhance conservation efforts to protect endangered turtle species and suggest new methods of human navigation, according to the researchers. The study was led by University of North Carolina marine biologists Kenneth and Catherine Lohmann along the Atlantic coast of Florida and was supported by a $413,000 grant from the National Science Foundation.

As newly hatched turtles leave the beach and enter the sea for the first time, they use the earth's magnetic field and the direction of ocean waves as crude compasses to guide them offshore into deeper waters favorable for growth and development. The young turtles, however, use the field primarily as a source of directional information for maintaining a heading.

"Older turtles," Lohmann said, "learn to use magnetic-field information in a far more sophisticated way, as a kind of map that can be used to pinpoint specific are....Read on....http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=100069&org=NSF