Sea Turtle Migrations

Sea turtles are slow-maturing animals that are known to make long transoceanic migrations, even returning back to their natal beaches. However, until very recently, the only knowledge of these journeys was available through the tracking of flipper tags when mature females ventured onto land to nest. Conservation organizations and governments have been monitoring these species for a number of years but with little, if any, level of recovery (Convis, 2001). Although only modest information is known about juvenile and male turtle movements, female turtles have been studied extensively by satellite telemetry due to nesting accessibility. It is hoped that by gaining a better understanding of turtle movements, migratory corridors and habitat use patterns can be established. The predominate source of information that has made monitoring a species that spends nearly its entire life in the open ocean possible, is the Argos/NOAA satellite-based location and data collection system. Satellite telemetry is really the only efficient technique available today to reconstruct the movements of oceanic animals. The Argos system is based on a system of Polar Orbiting Environmental Satellites (POES) that circle the earth every one hundred and one minutes and provide coverage of a 5000 km area over the earth's surface. The system classifies all signals into one of seven possible location classifications (3,2,1,0,A,B,Z), with 3 being the best possible positional accuracy (<150m). Researchers tend to use location classes of greater than or equal to 0, which have an estimated positional accuracy of <1000m. Usually, due to a high degree of error, location classifications of A,B, and especially Z (meaning that a signal is received but no location information can be obtained) are usually excluded from results (Cheng, 2000). In addition to providing positional information, which in turn can be used to track movements, the Argos system also provides detailed information about dive depth, dive duration and water temperature, as well as the ability to calculate average speed. The results of these tracking studies show that not only are sea turtles capable of making long transoceanic migrations, but they seemingly follow certain migratory routes. For instance, Luschi et al. (1998) tracked six green turtles (Chelonia mydas) from their nesting areas on Ascension Island (7˚57'S, 14˚22'W) to the coast of Brazil and found that their migratory paths were nearly identical even though they were released on separate dates. Arguments could certainly be made that these turtles were simply swimming in a westerly …