Sea turtles are known to rely on magnetic signatures to find their way thousands of miles to the beaches where they hatched. Researchers are now reporting in the journal Modern biology on May 6, there is some of the first solid evidence that sharks also rely on magnetic fields for their long-distance raids across the sea.
“It was not allowed how the sharks managed to orient themselves successfully during migration to target places,”
Researchers have known that some species of sharks travel long distances to reach very specific places year after year. They also knew that sharks were sensitive to electromagnetic fields. As a result, scientists have long suggested that sharks use magnetic fields for navigation. But the challenge was to find a way to test this in sharks.
“Honestly, I’m surprised it worked,” Keller said. “The reason this issue has been maintained for 50 years is that sharks are difficult to study.”
Keller realized that the necessary tests would be easier to perform on smaller sharks. They also needed a species known to return to certain places each year. He and his colleagues stopped at the heads of the hats (Sphyrna tiburo).
“The lid returns to the same mouth every year,” Keller said. “This shows that sharks know where the ‘home’ is and can move back to it from a distant place.”
The question then was whether the Bonechs managed these return journeys based on a magnetic map. To find out, the researchers used magnetic displacement experiments to test 20 juveniles caught by wild-headed bombs. In their research, they exposed the sharks to magnetic conditions, representing places hundreds of kilometers from where the sharks were actually caught. Such studies allow direct predictions of how sharks should subsequently orient themselves if they really rely on magnetic signals.
This video is footage from an experimental test where the swimming behavior of the lid is influenced by the magnetic field it is testing. Credit: Brian Keller
If sharks extract positional information from the geomagnetic field, the researchers predict a north orientation in the southern magnetic field and a south orientation in the northern magnetic field as sharks try to compensate for their sense of displacement. They did not predict an orientation preference when sharks were exposed to the magnetic field corresponding to their capture site. The sharks turned out to have acted as they had anticipated when exposed to flight in their natural range.
Researchers suggest that this ability to navigate based on magnetic fields may also contribute to the structure of the shark population. The findings in the bonnets also probably help explain the impressive exploits of other shark species. For example, a great white shark has been documented to migrate between South Africa and Australia, returning to the same place the following year.
“How great is it that a shark can swim 20,000 kilometers in a three-dimensional ocean and return to the same place?” Keller asked. “It’s really mind-boggling. In a world where people use GPS to navigate almost anywhere, this ability is truly remarkable. “
In future research, Keller says he would like to study the effects of magnetic fields from anthropogenic sources such as submarine cables on sharks. They would also like to study whether and how sharks rely on magnetic signals not only during long-distance migration, but also during their daily behavior.
Reference: “Using a Map of the Earth’s Magnetic Field in Sharks” by Brian A. Keller, Nathan F. Putman, R. Dean Grubs, David S. Portnoy and Timothy P. Murphy, May 6, 2021, Modern biology.
DOI: 10.1016 / j.cub.2021.03.103
This work was supported by the Save Our Seas Foundation and the Coastal and Marine Labs Laboratory of the University of Florida.