Sharks use their keen sense of smell for navigation as well as for feeding.

Andrew Nosal at the Scripps Institution of Oceanography in La Jolla, California, and his colleagues plugged the noses of wild leopard sharks (Triakis semifasciata) with cotton balls soaked in petroleum jelly, tagged the animals with acoustic transmitters and released them 9 kilometres offshore. Over roughly four hours, sharks without nose plugs swam two-thirds of the way back to shore in relatively straight paths, whereas sharks with plugged noses took more tortuous paths, swimming only one-third of the way back.

The sharks could be detecting gradients of chemicals that are associated with coastal marine life, such as dissolved amino acids, the authors say.

PLoS ONE 11, e0143758 (2016)