PERCEPTION OF WAVE SURGE MOTION BY HATCHLING SEA-TURTLES

At the beginning of their offshore migration, hatchling loggerhead sea turtles (Caretta caretta L.) enter the ocean and establish offshore h eadings while swimming near the substratum. In the shallow water of co astal areas, waves approaching the beach induce water near the ocean d oor to move toward and away from shore in a rhythmic, horizontal motio n known as wave surge. To determine whether hatchlings can detect wave surge and use it as a cue in orientation, we constructed a surge simu lator that produced movements closely resembling those that small, oce anic waves generate near the substratum. Hatchlings suspended in air a nd subjected to simulated surge approaching from their right or left s ides spent significantly more time attempting to turn than did turtles aligned parallel with the surge axis. These results demonstrate that turtles can indeed detect surge motion and orient along its axis. Such a response may play a brief but important role in enabling turtles to maintain offshore headings as they swim through shallow water to the open ocean. (C) 1998 Elsevier Science B.V. All rights reserved.