Researchers now have some of the first solid evidence that sharks rely on magnetic fields for their long-distance forays across the sea.
Researchers had known that some species of sharks travel over long distances to reach very specific locations year after year. They also knew that sharks are sensitive to electromagnetic fields. As a result, scientists had long speculated that sharks were using magnetic fields to navigate. But the challenge was finding a way to test this in sharks.
“The researchers realized their studies would be easier to do in smaller sharks. They also needed a species known for returning each year to specific locations. They settled on bonnetheads (Sphyrna tiburo). “The bonnethead returns to the same estuaries each year. This demonstrates that the sharks knows where ‘home’ is and can navigate back to it from a distant location,” said Bryan Keller, Florida State University Coastal and Marine Laboratory and Save Our Seas Foundation project leader.
The question then was whether bonnetheads managed those return trips by relying on a magnetic map. To find out, the researchers used magnetic displacement experiments to test 20 juvenile, wild-caught bonnetheads. In their studies, they exposed sharks to magnetic conditions representing locations hundreds of kilometers away from where the sharks were actually caught. Such studies allow for straightforward predictions about how the sharks should subsequently orient themselves if they were indeed relying on magnetic cues.
If sharks derive positional information from the geomagnetic field, the researchers predicted northward orientation in the southern magnetic field and southward orientation in the northern magnetic field, as the sharks attempted to compensate for their perceived displacement. They predicted no orientation preference when sharks were exposed to the magnetic field that matched their capture site. And, it turned out, the sharks acted as they’d predicted when exposed to fields within their natural range.”
“This research supports the theory that [sharks] use the earth’s magnetic field to help them find their way; it’s nature’s GPS…How cool is it that a shark can swim 20,000 kilometers round trip in a three-dimensional ocean and get back to the same site? It really is mind blowing. In a world where people use GPS to navigate almost everywhere, this ability is truly remarkable.”” -Bryan Keller
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Journal Reference: Bryan A. Keller, Nathan F. Putman, R. Dean Grubbs, David S. Portnoy, Timothy P. Murphy. Map-like use of Earth’s magnetic field in sharks. Current Biology, 2021; DOI: 10.1016/j.cub.2021.03.103