Shark's Sense of Smell: scientist sniffs out the subtleties of acute sense

We have long heard about a shark's acute sense of smell.  It's ability to detect the odors or scents given off by an injured fish was long considered one of a shark's primary tools in its predator tool kit. 

But just how sensitive is it?  With currents or water motion moving odors around, just how does a shark sense a smell and then begin tracking it to its source?  Dr. Jelle Atema has been studying sharks for some 20 years, working with the Boston University and the Woods Hole Oceanographic Institution.  He has spent considerable time investigating just how sharks utilize their sense of smell to their best advantage.

Reporting in BU Today, Susan Seligson writes of Dr. Atema's work with smooth dogfish, a small shark that is often found in the U.S. northeast (BTW: And one that has been severely hit by commercial shark fishing operations).  Using controlled plumes of odors like squid scent in a long observation tank, he is unlocking many of the secret subtleties as to how a shark senses odor and tracks it to its source.

Often we think of sharks as sensing the smell given off by an injured animal.  That may be true but, when hunting, sharks are attracted to the odors of familiar prey, injured or otherwise. 

“All animals give off some kind of body odor,” says Atema. “The science here is to understand how odor is dispersed into the water, and how many molecules does a shark need in his nose to track that odor.” 

Dr. Atema's experiments have also provided new insight as to how a shark responds to odors and how they just where to go to get to the source.  As reported in BU Today, "Working along with Jayne Gardiner at the University of South Florida, in Tampa, Atema’s most recent discovery is that sharks are guided by the nostril that first detects the prey’s odor, rather than orienting themselves based on which nostril senses the greater odor concentration. The finding—that smell reaches one nostril before the other, signaling whether to veer left or right—means that sharks can decipher very quickly, a matter of seconds as opposed to minutes, where their next meal is, no matter how chaotic the dispersed odor plume. Before this discovery, published in Current Biology, scientists had long believed that sharks’ sense of smell was a function of the plume’s surface area—the bigger the plume, the easier it would be for sharks to smell it." 

In some respects, the ocean is a very smelly place, full of scents or odors of hundreds of different organisms and at varying strengths or intensities.  Bombarded with all these stimuli, sharks can amazingly sort it all out and, along with its other senses, be the efficient predator that it is. 

Source: BU Today