Bonnethead sharks (Sphyrna tiburo) rely on magnetic fields for their long-distance journeys, according to new research led by scientists from the Florida State University Coastal and Marine Laboratory.
The bonnethead (Sphyrna tiburo). Image credit: Tony Hisgett / CC BY 2.0.
Migration is common in marine animals and use of the map-like information of Earth’s magnetic field appears to play an important role.
While sharks are iconic migrants and well known for their sensitivity to electromagnetic fields, whether this ability is used for navigation was unresolved.
“Our research supports the theory that they use the Earth’s magnetic field to help them find their way. It’s nature’s GPS,” said study’s lead author Dr. Bryan Keller, a researcher in the Florida State University Coastal and Marine Laboratory.
“Bonnetheads return 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,” he added.
The question then was whether bonnetheads managed those return trips by relying on a magnetic map.
To find out, Dr. Keller and colleagues used magnetic displacement experiments to test 20 juvenile, wild-caught bonnetheads.
In their experiments, they exposed sharks to magnetic conditions representing locations hundreds of km 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 scientists 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.
The authors suggest that this ability to navigate based on magnetic fields may also contribute to the population structure of sharks.
“How cool is it that a shark can swim 20,000 km round trip in a three-dimensional ocean and get back to the same site?” Dr. Keller said.
“It really is mind blowing. In a world where people use GPS to navigate almost everywhere, this ability is truly remarkable.”
The study was published in the journal Current Biology.
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Bryan A. Keller et al. Map-like use of Earth’s magnetic field in sharks. Current Biology, published online May 6, 2021; doi: 10.1016/j.cub.2021.03.103
