Some animals are believed to use information about the earth's magnetic field to navigate from place to place, but a sensory mechanism has yet to be established for how animals detect magnetic compass information. In the ocean, sharks and rays have a sensory system of electroreceptors, related to the lateral line system of several other fishes. This electrosensory system has been extensively studied physiologically and behaviorally, and has extremely high sensitivity to very tiny electrical currents that are used for locating prey. Ocean water and living organisms are salty and electrically conductive, and the physics of electromagnetism means that motion of a conductor through a magnetic field induces an electrical current. A shark has organs sufficiently sensitive to detect the electrical field induced by its own motion through the earth's magnetic field, and so theoretically is able to orient to a magnetic compass heading. This project utlilizes a unique electromagnetic research facility, specially constructed for behavioral tests while allowing the creation of artificial uniform electric and magnetic fields in a large seawater tank. These fields can be made to simulate or to exactly cancel fields of the sort that the fish encounter naturally, corresponding to their swimming speed and direction. Behavioral tests will show whether the electrosensory system is necessary and sufficient for an animal to swim toward a correct target based a magnetic compass reference system. Instead of searching for a new sense organ for magnetic sensitivity, this project is a direct test of whether sharks and rays actually utilize the information already available to their electrosensory system. Results will be a clear validation or refutation for the first time in any animal of a sensory mechanism for magnetic compass orientation, and so will have an impact on a long-standing controversy in animal behavior as well as neuroscience. Additional impact will come from making the facility itself available as a resource for others in the field.
