Regional magnetic fields as navigational markers for sea turtles

Young loggerhead sea turtles (Caretta caretta) from eastern Florida underta ke a transoceanic migration in which they gradually circle the north Atlant ic Ocean before returning to the North American coast. Here we report that hatchling loggerheads, when exposed to magnetic fields replicating those fo und in three widely separated oceanic regions, responded by swimming in dir ections that would, in each case, help keep turtles within the currents of the North Atlantic gyre and facilitate movement along the migratory pathway . These results imply that young loggerheads have a guidance system in whic h regional magnetic fields function as navigational markers and elicit chan ges in swimming direction at crucial geographic boundaries.