The navigational feats of green sea turtles migrating from Ascension Island investigated by satellite telemetry

Previous tagging studies of the movements of green turtles (Chelonia mydas) nesting at Ascension Island have shown that they shuttle between this remo te target in the Atlantic Ocean and their feeding grounds on the Brazilian coast, a distance of 2300 km or more. Since a knowledge of sea turtle migra tion routes might allow inferences on the still unknown navigational mechan isms of marine animals, we tracked the postnesting migration of six green t urtle females from Ascension Island to Brazil. Five of them reached the pro ximity of the easternmost stretch of the Brazilian coast, covering 1777-234 2 km in 33-47 days. Their courses were impressively similar for the first 1 000 km, with three turtles tracked over different dates following indisting uishable paths for the first 300 km. Only the sixth turtle made some relati vely short trips in different directions around Ascension. The tracks show that turtles (i) are able to maintain straight courses over long distances in the open sea; (ii) may perform exploratory movements in different direct ions; (iii) appropriately correct their course during the journey according to external information; and (iv) initially keep the same direction as the west-south-westerly flowing current, possibly guided by chemical cues.