Homing in green turtles Chelonia mydas: Oceanic currents act as a constraint rather than as an information source

Abstract

As open sea navigators, green turtles Chelonia mydas have to deal with oceanic currents. These currents may have a mechanical influence, forcing turtles away from their desired course, but they may also provide information to navigating turtles by bringing chemical cues down-current from their target area. In the present paper, we have introduced new path analysis methods, coupling remote-sensing oceanographic data and satellite-tracking data in order to test these hypotheses. These methods were exemplified on the homing routes of 3 green turtles nesting on Europa, an isolated island in the southern part of Mozambique Channel. The turtles, displaced by ship east-southeast from Europa, returned to their nesting island in 13 to 59 d, following long, circuitous routes, and hence apparently displaying poor navigational abilities. Path analysis showed that turtles were unable to compensate for the deflecting action of currents, which moved them away from their intended course and lowered their orientation performance. At large distances from Europa, green turtles did not appear to find navigational information in water masses that had previously been in contact with their target area. © Inter-Research 2006.