Turtle Migration

Sea turtles have a migration pattern somewhat similar to that of salmon. Adult females migrate to their natal beach and lay eggs in the sand. Hatchlings undergo a short but high-risk, due to predators, journey to the shoreline, and then swim to the open ocean. Initially their swimming direction is oriented into the waves; near shore the waves provide an indication of the direction of the open ocean. Their migration then continues for hundreds or thousands of kilometers into the ocean, into favorable feeding grounds.
Even less is known about how sea turtles accomplish this feat than is known for salmon. Turtles may actually use the geomagnetic field to tell them their location (of course, the open ocean has no landmarks); if this is the case, then their magnetoperception system seems to work on a more refined level than that of birds, which is thought to provide directional but not locational information.
Some scientists think that sea turtles probably use the geomagnetic field to orient their swim in the deep ocean, but they would also have celestial cues available to them. However, an experiment in which magnets were fitted to the heads of green turtles migrating between the open Atlantic and Brazil found that the turtles with magnets performed as well as their counterpart controls.
The directional vector of sea turtles is probably determined genetically, although their is no data to support this assumption. Also intriguing but unexplained is their ability to find their way precisely back to their natal beach over their vast travel distance. Do they imprint, as salmon do, on olfactory features in the water? Or is the location pinpointed using geomagnetic information?

Goff M, Salmon M, Lohmann KJ 1998 Hatchling sea turtles use surface waves to establish a magnetic compass direction Animal Behaviour 55: 69-77
Lohmann KJ, Lohmann CMF 1998 Migratory guidance mechanisms in marine turtles Journal Of Avian Biology 29: (4) 585-596
Lohmann KJ, Hester JT, Lohmann CMF 1999 Long-distance navigation in sea turtles Ethology Ecology & Evolution 11: (1) 1-23
Papi F, Luschi P, Akesson S, Capogrossi S, Hays GC 2000 Open-sea migration of magnetically disturbed sea turtles Journal Of Experimental Biology 203: (22) 3435-3443

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copyright ©2001 Michael D. Breed, all rights reserved