Sharks use the Earth’s magnetic field as a sort of natural GPS to navigate journeys that take them great distances across the world’s oceans, scientists have found.
Researchers said their marine laboratory experiments with a small species of shark confirmed long-held speculation that sharks use magnetic fields as aids to navigation — behaviour observed in other marine animals such as sea turtles.
Their study, published in the journal Current Biology, also shed light on why sharks are able to traverse seas and find their way back to feed, breed and give birth, one of the study authors said.
“We know that sharks can respond to magnetic fields,” marine policy specialist Bryan Keller said.
“We didn’t know that they detected it to use as an aid in navigation … You have sharks that can travel 20,000 kilometres (12,427 miles) and end up in the same spot.”
The question about how sharks perform long-distance migrations has intrigued researchers for years.
The sharks undertake their journeys in the open ocean where they encounter few physical features such as corals that could serve as landmarks.
Looking for answers, scientists based at Florida State University decided to study bonnethead sharks — a kind of hammerhead shark that lives on both American coasts and returns to the same estuaries every year.
Researchers exposed 20 bonnethead sharks to magnetic conditions that simulated locations hundreds of kilometres away from where they were caught off of Florida.
The scientists found that the sharks began to swim north when the magnetic cues made them think they were south of where they should be.
This finding was compelling, Robert Hueter, senior scientist emeritus at Mote Marine Laboratory & Aquarium said.
Mr Hueter, who was not involved in the study, said further research was needed to find how the sharks used the magnetic fields to determine their location and whether larger, long-distance migrating sharks used a similar system to find their way.
“The question has always been: Even if sharks are sensitive to magnetic orientation, do they use this sense to navigate in the oceans, and how? These authors have made some progress at chipping away at this question,” he said.
Mr Keller said the study could help inform management of shark species, which were in decline.
Research this year found that worldwide abundance of oceanic sharks and rays had fallen more than 70% between 1970 and 2018.
Researchers said the bonnethead’s reliance on Earth’s magnetic field was probably shared by other species of shark, such as great whites, that made cross-ocean journeys.
Mr Keller said it was very unlikely that bonnethead sharks evolved with a magnetic sensitivity and other travelling sharks did not.