Thursday, March 3, 2011

Sharks on the Right Path: research indicates predators know where they're going

Researchers continue to learn more about the movement of sharks, particularly their ability to navigate along deliberate paths as opposed to random, meandering movements. Much attention has been paid in recent years to the incredible long-distance migrations that many species of shark undertake. But scientists with the Florida Museum of Natural History focused their attention on shorter distances; in essence, how and where the sharks traveled over several days or weeks as opposed to many months. What they found was that sharks at times appear to know exactly where they are going.

The Florida researchers tracked the movements of tiger, thresher, and blacktip reef sharks, and their results, recently published in the Journal of Animal Ecology, showed that the sharks would often exhibit random movements or "walks." However, there were plenty of times when the sharks, particularly the tigers, would demonstrate very directional movement behavior. The tiger sharks appeared to be the best at pursuing these directed walks, covering as much as 30 miles in a singular direction and even traveling several miles to a very specific point underwater.

Yannis Papastamatiou, co-author of the study, said, "Our research shows that, at times, tiger sharks and thresher sharks use highly directed walks to swim to specific locations. Simply put, they know where they are going.

Many people could walk to a known destination 3.7 to five miles away, but imagine doing it in deep water and at night.

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."

As a diver, I can attest as to how difficult visual navigation can be underwater. Rock formations that appear one way as you move in a particular direction can look completely different when approached from the reverse direction or different angle. But with a full range of sensory capabilities far beyond that of man, using visual cues combined with other sensory input like temperature, currents, or even the magnetic fields of the earth could make it simply all in a day's work for a shark.

In June of last year, I wrote about similar research studying a variety of pelagic - or open-ocean - predators like swordfish, tuna, and sharks. In this study, the researchers were looking for certain mathematical patterns: Brownian walks for so-called random movements, and Levy flights for more directional straight movements. One of the researchers noted that the use of straight line movements as opposed to random may have been initiated due to the availability of food.

Lévy behavior showed up more often in waters where plankton, fish and other food was scarce. In regions with plentiful food, random motion dominated. This observation, says theoretical physicist Gandhimohan Viswanathan, fits with earlier suggestions that 'animals may use a Lévy flight motion to improve their chances of finding prey.'”

Whether motivated by food or some other impulse or whether or not supported by a keen sense of visual direction or some other ability (all questions to be answered with future research), it can be said that in a challenging environment like the ocean, sharks are being shown to demonstrate some highly intelligent movement behaviors, perhaps relying on some "cognitive maps" lodged somewhere deep within their brains.

Read about shark movements in U.K.'s Mail Online.
Read about Brownian walks and Levy flights in RTSea Blog.

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