Sharks Use Their Noses to Find Their Way

One of the mysteries of marine animals is how they find their way around in a world with no landmarks. Many sharks, for instance, live in the pelagic zone—the part of the ocean that’s neither near the seafloor nor any visible shoreline. So how do they navigate, reliably migrating to the same places year-to-year? (One popular annual gathering place between Baja California and Hawaii has been likened to a Burning Man for great whites.) They use their sense of smell, according to a new study in the journal PLOS ONE.

Sharks use their keen sense of smell to do more than find their way to a wounded seal, according to researchers led by University of California San Diego marine biologist Andrew Nosal. The researchers captured 26 leopard sharks off the coast of San Diego and inserted petroleum-jelly-covered swabs into the nares (the shark version of a nostril) of 11 sharks. As a control, the team mimicked inserting cotton into the nares of the remaining sharks but didn’t actually insert any cotton. Then, using a tank that blocked the sharks from seeing or from sensing magnetic fields that might guide them, he transported them an hour northwest and released them with tags and sensors attached to them to track their movements. He also captured and released 10 sharks on a different day without interfering with their senses of smell.

He found that sharks that couldn’t smell swam slower and did not spend as much time swimming toward shore as the control sharks. The sharks that had no wool shoved up their noses swam very quickly in straight paths back to shore, while those that couldn’t smell appeared disoriented. Their paths approximated a “random walk,” according to the study, though they did lean towards heading for shore, suggesting that they might have gotten there eventually. Nosal and his team hypothesize that the sharks might be smelling chemicals associated with chlorophyll that exists in greater quantities nearer to the coast in California.