Sharks respond to magnetic fields
(CNN) -- Marine scientists in Hawaii have confirmed sharks can spot changes in magnetic fields.
The discovery adds weight to the long-held theory that the fish possess an internal compass to guide them over long distances.
The University of Hawaii biologists reported in Britain's Royal Society journal that the captive fish -- six sandbar sharks and one scalloped hammerhead shark -- were tested using food and an artificial magnetic field.
The six-week trials showed the sharks were able to detect feeding sites solely through the use of magnetic fields, even when food was not present.
When the artificial field was activated, the sharks changed from their usual cruising of the tank to swimming more excitedly, homing in on the target in anticipation of finding food.
This behavioral change resulted in many more passes over the target with the artificial field activated than when switched off.
Before the tests, the theory that sharks used magnetic guidance to cruise long distances across oceans in straight lines was circumstantial.
But the Hawaiian-based researchers say their results reinforce this theory.
"Unequivocal behavioral responses to earth-strength magnetic stimuli have proven elusive in most other animals," the report said.
"But the strong response shown by the captive sharks provides a robust behavioral assay that can now be used to precisely determine how sharks detect magnetic fields and to measure detection thresholds."