Sunday, March 6, 2011

Sharks - dazzling navigators

Sharks are famed for extraordinary hearing, motion sensing and smell, but new research shows some shark species can also navigate with pinpoint accuracy over long distances.

"Many people could walk to a known destination six to eight kilometers (five miles) away -- but imagine doing it in deep water and at night."

US ecologists analyzed data from eight tiger sharks, nine black-tip reef sharks and 15 threshers which had been tagged with trackers and released off Hawaii, Palmyra atoll in the Pacific or southern California before being followed for between seven and 72 hours.The blacktip reef sharks all swam apparently randomly within a narrow home range, while the tiger and thresher sharks travelled longer distances, often with a clear sense of direction.

The biggest voyagers were the tiger sharks, which during the study period swam over eight kilometres. Some research has tracked this species heading to a goal 50 kilometres away."Directed movement" reflects terrain that is familiar for the sharks, given that they have an interest in saving energy by heading straight towards a target, such as food, says the study.

The mystery remains, though, of how sharks are able to accomplish navigational feats."

Theories to explain the sharks' tricks include "cognitive maps" built on knowledge of ocean currents and temperatures, which act in the same way as visual landmarks on the ground, or perhaps navigation by Earth's magnetic field.

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