The Offshore Migration

Hatchling loggerhead sea turtles from eastern Florida, U.S.A., use three different sets of orientation cues sequentially as they migrate offshore to the Gulf Stream. Hatchlings that have just emerged from their underground nests on the beach crawl seaward by orienting toward the low, bright oceanic horizon. Once turtles enter the ocean, they initially establish an offshore heading by swimming into waves. Because waves are refracted in shallow, coastal areas until they approach the beach directly, swimming into waves reliably leads turtles seaward.

In deeper water farther from land, waves can move in any direction relative to the coastline and no longer provide a reliable indicator of offshore direction. Nevertheless, hatchlings tracked from a Florida beach into the open ocean continued on the same seaward headings after entering offshore areas where wave direction no longer coincided with their established courses. Experiments have revealed that hatchlings can transfer a course initiated on the basis of wave cues to a course maintained by a magnetic compass. This transfer of directional information may enable turtles to maintain offshore headings even after swimming beyond the wave refraction zone.

The diagram above summarizes the orientation cues that are thought to guide hatchling Florida loggerheads from their nests to the Gulf Stream Current. The beach is to the left and progressively deeper water is to the right. Lines represent oceanic waves moving toward the beach; as they enter shallow coastal areas, waves refract until they approach the beach directly.

Click on the three turtles in the diagram to learn more about how hatchlings guide themselves during each part of the migration.