Map-like use of Earth's magnetic field in sharks.

Migration is common in marine animals, and use of the map-like information of Earth's magnetic field appears to play an important role. While sharks are iconic migrants and well known for their sensitivity to electromagnetic fields, whether this ability is used for navigation is unresolved. We conducted magnetic displacement experiments on wild-caught bonnetheads (Sphyrna tiburo) and show that magnetic map cues can elicit homeward orientation. We further show that use of a magnetic map to derive positional information may help explain aspects of the genetic structure of bonnethead populations in the northwest Atlantic. These results offer a compelling explanation for the puzzle of how migratory routes and population structure are maintained in marine environments, where few physical barriers limit movements of vagile species. VIDEO ABSTRACT.