Might be time to re-think your strategy for avoiding sharks: turns out the marine predators use the Earth’s magnetic field to navigate, according to new research from the US.
The study has produced the first firm evidence that bonnethead sharks – a small type of hammerhead found in American waters – like birds and turtles, use magnetic fields to figure out where they are and where to go.
Marine biologists knew that sharks could navigate to specific locations over long distances repeatedly over several years.
They also knew that sharks were sensitive to electromagnetic fields, but they’d been unable to find evidence connecting the two things.
Researchers based at Florida State University have used an experiment on bonnethead sharks to show there’s a connection.
“To be honest, I am surprised it worked,” says study leader Bryan Keller. “The reason this question has been standing for 50 years is because sharks are difficult to study.”
Keller and colleagues captured 20 juvenile bonnethead sharks (Sphyrna tiburo) from the wild and put them in tanks.
A bonnethead being transported to holding facilities at the FSU Coastal and Marine Lab. Credit: Bryan Keller
After the animals had a few weeks to acclimatise, the team watched the sharks as they applied artificial magnetic fields to the tanks, designed to simulate two locations: one 600km north of the capture area, and one 600km south.
The sharks oriented themselves randomly in the (unmagnetised) control setting, but once the ‘northern’ magnetic field was applied, they faced south.
Likewise, they turned north in the ‘southern’ magnetic field. “In the southern treatment, they did preferentially occupy certain parts of the tank,” adds Keller.
The sharks’ actions corresponded to directions they would be going if they were in the wild in these locations.
Keller says it would have been impossible for the sharks to have experienced the northern magnetic fields before, meaning they weren’t doing this by memory. “The magnetic fields [they] were exposed to for the northern treatment actually occurred on land,” he says.
The researchers say this provides evidence as to how sharks can navigate across long distances.
“How cool is it that a shark can swim 20,000 kilometres round trip in a three-dimensional ocean and get back to the same site?” says Keller.
“It really is mind blowing.
“In a world where people use GPS to navigate almost everywhere, this ability is truly remarkable.”
The research paper has been published in the journal Current Biology.
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Ellen Phiddian is a science journalist at The Royal Institution of Australia.
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