Leopard Sharks may navigate the ocean using their sharp sense of smell, according to a new study.
For the study – published January 6 in the journal PLOS ONE – the researchers caught some leopard sharks (Triakis semifasciata) and took them about nine kilometres (six miles) away from shore. Then, they stuffed some of the sharks’ noses with cotton (soaked in Vaseline) and released the sharks back into the water to see whether those with impaired sense of smell would be able to find their way back to shore.
Final results showed that the sharks with plugged noses appeared to be lost, compared with the other ones who quickly found their way back to shore.
Andrew Nosal, lead researcher of the study and a postdoctoral researcher at the Scripps Institution of Oceanography and the Birch Aquarium in California, said that they essentially ‘kidnapped’ the sharks, and confused them for about an hour after taking them to a specific location. Even so, thirty minutes after being released into the water, those without nose plugs found their way back to shore without any difficulty.
According to Nosal, it is well known that sharks are very skilled navigators, but scientists are still unsure which senses they use (smell, sight, magnetic or electric senses) to travel along straight paths toward their target.
Evidence that sharks heavily rely on their sense of smell is that their – which is located in the brain – is larger in those shark species that have to navigate longer routes, Nosal stated.
To test this, he and his colleagues ‘kidnapped’ 26 female leopard sharks, which they found off the coast of La Jolla in Southern California. They put them in a holding tank on the boat and covered them with a tarp. Researchers then drove the boat to a specific point, located nine kilometres offshore. To confuse the sharks, they hung a strong magnet on the boat and drove in figures of eight, or other random patterns.
Jelle Atema, a professor of biology at Boston University Marine Program, said that sharks breathe through their gills, so temporary nose plugs would not have limited their oxygen intake. In the study, 15 of the leopard sharks received no nose plugs, while 11 received plugs.
Only about one-third of the sharks with nose plugs managed to find their way back to shore within four hours, compared with two-thirds of those without nose plugs, the researchers found. The leopard sharks with nose plugs also had more random routes.
However, even the sharks with nose plugs managed to get to shore, which goes to show that these animals rely on more than the sense of smell to navigate the vast ocean, Nosal said.
Image Source: wikimedia
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