The Built-In Magnetic “GPS” of Sharks

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 navigate to and from a precise place repeatedly. 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.