The secret behind sharks sniffing out their prey



The secret behind sharks sniffing out their prey  Washington: It's no secret that sharks have a keen sense of smell and a remarkable ability to follow their noses through the ocean, right to their next meal.

Now, researchers have figured out how the sharks manage to keep themselves on course.

It turns out that sharks can detect small delays, no more than half a second long, in the time that odours reach one nostril versus the other, the researchers report.

When the animals experience such a lag, they will turn toward whichever side picked up the scent first.

"The narrow sub-second time window in which this bilateral detection causes the turn response corresponds well with the swimming speed and odour patch dispersal physics of our shark species known as Mustelus canis or the smooth dogfish," said Jayne Gardiner of the University of South Florida (USF).

All in all, it means that sharks pick up on a combination of directional cues, based on both odour and flow, to keep themselves oriented and ultimately find what they are looking for.

If a shark experiences no delay in scent detection or a delay that lasts too long -- a full second or more -- they are just as likely to make a left-hand turn as they are to make a right.

These results refute the popular notion that sharks and other animals follow scent trails based on differences in the concentration of odour molecules hitting one nostril versus the other. It seems that theory doesn't hold water when one considers the physics of the problem.

"There is a very pervasive idea that animals use concentration to orient to odours," Gardiner said.

Indeed, Gardiner explained, recent studies have shown that concentrations of scent molecules could easily mislead.

"This discovery can be applied to underwater steering algorithms," Gardiner said. "Previous robots were programmed to track odours by comparing odour concentrations, and they failed to function as well or as quickly as live animals."

"With this new steering algorithm, we may be able to improve the design of these odour-guided robots," Gardiner added.

"With the oil spill in the Gulf of Mexico, the main oil slick is easily visible and the primary sources were easy to find, but there could be other, smaller sources of leaks that have yet to be discovered. An odour-guided robot would be an asset for these types of situations."

The story is based on materials provided by Cell Press.

These findings were reported online in the June edition of Current Biology.

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