Geomagnetic Imprinting as a Mechanism of Natal Homing in Sea Turtles and Salmon

Diverse marine animals, including sea turtles, anadromous fishes, and marine mammals, migrate vast distances across seemingly featureless ocean before returning as adults to their area of origin to reproduce.  How animals accomplish such feats of natal homing has remained an enduring mystery, but growing evidence supports the hypothesis that some animals imprint on the unique magnetic signature of their natal area and then use magnetic map information to help them return years later.  In both sea turtles and salmon, subtle changes in the geomagnetic field of the home region are correlated with changes in natal homing behavior, providing strong evidence that geomagnetic information plays a role in guiding reproductive migrations.  In salmon, a biphasic navigational strategy appears likely, in which an open-sea navigation phase mediated by magnetic cues guides salmon into the vicinity of the home river, close enough for chemical cues to allow completion of the spawning migration.  The ability to derive positional information from Earth’s magnetic field may thus be the centerpiece of long-distance natal homing in sea turtles, salmon, and numerous other ocean migrants.