March 2, 2011

Navigating The Oceans With Sharks

Researchers, writing in the Journal of Animal Ecology suggest that some shark species have "mental maps" of their ranges and can pinpoint locations in the ocean up to 30 miles away.

Tagged with acoustic transmitters, scientists analyzed data from tiger sharks, and found that they took directed paths from place to place, AFP is reporting.

Using nine Blacktip reef sharks and 15 Threshers which had been tagged with trackers and released off Hawaii, Palmyra atoll in the Pacific or southern California, the sharks were then 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 farther, and with an apparent clear sense of direction.

Sharks are long known for extraordinary hearing, motion sensing and smell. New research is showing some shark species can also navigate with pinpoint accuracy over long distances.

"Simply put, they know where they are going," said Yannis Papastamatiou of the Florida Museum of Natural History, who co-authored the study published Wednesday. "Many people could walk to a known destination five miles away -- but imagine doing it in deep water and at night."

Tiger sharks were found to have the largest mental maps of the species studied, which during the study period swam over 5 miles. Some research has tracked this species heading to a goal 25 miles 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. "As anyone who dives knows, finding your way around underwater without a compass is very difficult, but this is what we found tiger sharks could do," Papastamatiou explained to BBC News.

Explaining the sharks' skills include theories such as "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.

Yellowfin tuna, apparently do this using small amounts of the mineral magnetite in their heads, sharks do not appear to maintain deposits of this magnetic sensor.


Image Caption: This is a blacktip reef shark. Credit: Copyright Yannis Papastamatiou


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