benefit? The study has shown that the marine turtles navigation system allows them to maintain their course towards the egg-laying site wherever they find themselves. It is almost as if they were equipped with a compass pointing towards the beach in question. So they can correct any deflection they are subject to: transport by boat, ocean currents But, unlike human navigators, they are not able to correct for ocean drift in plotting their course. So the movements recorded by the satellite are a combination of deliberate action by the turtles and the effect of currents. So it appears that the turtles navigation system is relatively simple and may cause them to be wander at sea for long periods during adverse ocean conditions. One turtle released 250 km from its egg-laying site on Europa traveled more than 3 500 km in two months before returning there!

In the second experiment, the researchers have studied the effect of the earths magnetic field on the turtles navigation system. They have shown, for the first time in natura, that marine turtles use the magnetic field of the earth to orientate themselves. When this field is disturbed by placing a powerful magnet on their heads, turtle navigation is not as good. But the fact that they can still return to their original egg-laying site shows that the geomagnetic field is not the only information source that they use. Researchers think the turtles may also use their sense of smell like certain sea birds or homing pigeons. This hypothesis remains to be proven

This work should improve conservation strategies for marine turtles, an endangered, officially protected species, by providing a better understanding of how they manage these long migrations between egg-laying and feeding areas.

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Contact: Monica McCarthy
monica.mccarthy@cnrs-dir.fr
0033-196-445-191
CNRS
26-Feb-2007

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