Marine turtles almost always return to the same beach to lay their eggs. The egg-laying sites are often far from the feeding areas and the females cross several hundred kilometers of ocean with no visual landmarks. How do they manage to return to the same spot? A study by Simon Benhamou of the Center for Functional and Evolutionary Ecology at Montpellier1, France, together with other groups (CNRS, IRD, IFREMER, CEDTM2, University of Pisa), shows that the marine turtles use a relatively simple navigation system involving the earths magnetic field, and this allows them to return to the same egg-laying site without having the ability to correct for the deflection of ocean currents. This work, published in Current Biology and Marine Ecology Progress Series, should allow better conservation strategies for this endangered species.
Every 4 years, on average, Indian Ocean green turtles (Chelonia mydas) travel hundreds of kilometers to specific egg-laying areas, where they will lay 4 to 6 successive clutches. To better understand the navigation process and the sensory channels involved in this long-distance oceanic travel, the researchers have conducted a multidisciplinary study, involving biology and physical oceanography, in two series of experiments. In the Mozambique Channel, between the east coast of Africa and Madagascar, on the beaches of the French Islands of Europa and Mayotte, they caught turtles at the beginning of their egg-laying cycle, so that the animals were strongly impelled to return to this area to complete their cycle. After having Argos transmitters fitted to their shells in order to satellite track their return journey to the beach, the animals were released in open sea, several hundred kilometers from the egg-laying site.
The first experiment was to study the navigation system of the marine turtles and discover how they detect the ocean currents: are the turtles movements controlled by the currents or can they use them to their
Contact: Monica McCarthy