Scientists have discovered that sharks use the Earth's magnetic field as a natural navigation system to help them travel far across oceans.
Researchers say their experiment with a small shark species confirms long-suspected sharks use magnetic fields to aid navigation -- a behavior that has also been observed in other Marine animals, such as turtles.
Ocean policy expert Brian Keller, one of the report's authors, said the study also revealed how sharks are able to cross the ocean and return to feed and breed. The study was published this month in the US journal Current Biology.
"We know sharks respond to magnetic fields," Keller said. But we didn't know they were sensing magnetic fields to help navigate... Some sharks can swim 20,000 kilometers and come back."
For years, researchers have wondered how sharks migrate long distances. Sharks swim in the open ocean and rarely encounter landmarks such as coral.
To find out, scientists at Florida State University decided to study the narrow head hammerhead sharks, which live on both coasts of the United States and return to the estuaries where they used to live each year.
Researchers caught 20 hammerhead sharks off the coast of Florida and exposed them to simulated magnetic conditions hundreds of kilometers from where they were caught, the report said. Scientists found that when the magnetic signals made the sharks think they were south of where they should be, they began to swim north.
Robert Schutt, a senior scientist emeritus at the Mott Institute of Oceanography who was not involved in the study, says the finding is compelling.
Huetter said further research is needed to determine how the shark uses the magnetic field to locate itself, and whether larger sharks that migrate long distances use a similar system to navigate.
"The question has always been: even if sharks are sensitive to the direction of magnetic fields, do and how do they use that sense to navigate the ocean? These authors have made some progress in dissecting this problem."
Keller says the study could help inform efforts to manage dwindling shark populations. A study this year showed that the global population of oceanic sharks and rays declined by more than 70 percent from 1970 to 2018.
Like the scalloped hammerhead shark, most other oceanic migratory shark species, such as the great white shark, depend on the Earth's magnetic field, the researchers said. Keller says it's unlikely that only the narrow-headed hammerhead shark has evolved the ability to sense magnetic fields while other migratory sharks have not.