Magnetic map shows the way for migrating sea turtles

The mystery of the migrating sea turtle may have been solved by scientists who have shown that the creature can use the Earth's magnetic field as both a compass and a map.

An experiment by marine biologists in Florida has demonstrated the phenomenal ability of the green sea turtle to sense subtle variations in the Earth's magnetic field.

Turtles migrate thousands of kilometres over open ocean and the research suggests they can sense small perturbations in the north-south direction of the magnetic field both to work out where they are and where they should be going.

Green sea turtles are especially accurate in their migration, with some of them commuting from the same feeding and breeding sites off the coast of Brazil to Ascension Island, a tiny dot just 10km wide in the middle of the South Atlantic.

The scientists, from the University of North Carolina, studied the turtles' homing instincts using a giant magnetic coil built around an aquarium.

They used the coil to reproduce magnetic fields known to exist at locations along the Florida coast so they could expose captive turtles to fields from widely different places.

The study found turtles exposed to a northern field swam south, while those in the southern field swam towards the north.

The researchers said the results implied turtles "have a kind of magnetic map. In other words, they can figure out where they are relative to home using magnetic-field information".

- INDEPENDENT