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The Magnetic “GPS” of Sharks
Bonnethead sharks may use Earth’s magnetic field to
navigate as they migrate over long distances at sea.
Credit: D. Ross Robertson, Smithsonian Institution.
Great whites, makos, blue sharks—these are a handful of the shark
species that migrate thousands of miles each year, but scientists have
struggled to figure out how these sharks know how to get where they’re
going. A study with more than a dozen juvenile bonnethead sharks has
finally offered some answers. Sharks, like sea turtles, appear to use the
Earth’s magnetic field to navigate the seas.
Because large sharks are so difficult to study in the open ocean, scientists from the Save Our Seas Foundation and Florida State University decided to conduct a controlled experiment with 20 young bonnetheads that the researchers had caught in the wild. Bonnetheads visit the same estuaries each year, so they had already demonstrated the ability to repeatedly navigate to and from a precise place. Scientists already knew that sharks are sensitive to electromagnetic fields. So, the researchers noted the swimming habits of these young sharks and then adjusted the magnetic conditions around them to match the magnetic “signature” of locations hundreds of miles away from where the sharks had been caught. If the sharks didn’t alter their swimming direction or behavior after the change, then they weren’t relying on the magnetic field to guide them. But if the sharks reoriented themselves in the direction that would be “home” in the adjusted magnetic field, that would reveal their ability to navigate based on electromagnetic signals.
The sharks didn’t swim in any particular direction when the magnetic field matched where they’d been caught, but they did head toward “home” when the magnetic field matched a distant location. The results confirmed that sharks may rely on magnetic fields to make their way thousands of miles across the ocean to the exact waters they visit year after year.
Because large sharks are so difficult to study in the open ocean, scientists from the Save Our Seas Foundation and Florida State University decided to conduct a controlled experiment with 20 young bonnetheads that the researchers had caught in the wild. Bonnetheads visit the same estuaries each year, so they had already demonstrated the ability to repeatedly navigate to and from a precise place. Scientists already knew that sharks are sensitive to electromagnetic fields. So, the researchers noted the swimming habits of these young sharks and then adjusted the magnetic conditions around them to match the magnetic “signature” of locations hundreds of miles away from where the sharks had been caught. If the sharks didn’t alter their swimming direction or behavior after the change, then they weren’t relying on the magnetic field to guide them. But if the sharks reoriented themselves in the direction that would be “home” in the adjusted magnetic field, that would reveal their ability to navigate based on electromagnetic signals.
The sharks didn’t swim in any particular direction when the magnetic field matched where they’d been caught, but they did head toward “home” when the magnetic field matched a distant location. The results confirmed that sharks may rely on magnetic fields to make their way thousands of miles across the ocean to the exact waters they visit year after year.