Sharks navigate using Earth’s magnetic field

Sea turtles, lobsters and some birds rely on Earth’s magnetic field to navigate to the beach of their birth or their winter getaway during migration. On May 7, 2021, researchers reported the first evidence that sharks, which are more difficult to study, are included in the group of animals that have a magnetic sense, making it possible to map their surroundings and to maintain their heading while navigating long distances, using Earth’s magnetic field. The video above (by B. Keller) is footage from an experimental trial, where a bonnethead shark is experiencing a magnetic field, which affects its swimming behavior.

The scientists published their research in the peer-reviewed journal Current Biology on May 6, 2021.

Bryan Keller at Florida State University Coastal and Marine Laboratory is the lead author of this research. He said:

It had been unresolved how sharks managed to successfully navigate during migration to targeted locations. This research supports the theory that they use the Earth’s magnetic field to help them find their way; it’s nature’s GPS.

Scientists already knew that some sharks travel far, year after year, to the same specific locations. For example, a great white shark was known to swim back and forth between Australia and South Africa, always to precisely the same location as the previous year. Keller said of this feat:

How cool is it that a shark can swim 20,000 kilometers (12,400 miles) 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.

Bearded man on a boat out in the ocean, holding up a small shark.
Biological oceanographer Bryan Keller is the lead author of a paper reporting how sharks use Earth’s magnetic field to navigate large distances. Image via Colby Griffiths/ Save Our Seas Foundation.

Scientists also knew that sharks are sensitive to electromagnetic fields. So the results of this research have long been a source of speculation … but a speculation hard to test. Keller said of his research method:

To be honest, I am surprised it worked. The reason this question has been withstanding for 50 years is because sharks are difficult to study.

A shark with a big round head seen from below against a black background.
The researchers used Bonnetheads – a small shark known for returning to the same places – to test how they are affected by changes in magnetic field around them. Image via D Ross Robertson/ Wikimedia Commons.

In order to get the answers they were seeking, the researchers used bonnetheads, the smallest shark in the hammerhead family. These sharks are known to return to the same estuaries – transition zones between rivers and oceans – each year.

To find out whether bonnethead sharks rely on a magnetic map to find their way, the researchers set up a cage-like structure with copper wires around a shark pool. They created magnetic field conditions as they would exist at different locations on Earth, hundreds of kilometers apart in a north-south direction, by applying a current through the wiring. They then tested the simulated locations on 20 young bonnetheads caught in the wild, one at the time. If the sharks could sense the fields, they would then move to the north in a field simulated to be in the south. Likewise, they would turn to the south in the field simulated to be in the north, in their effort to return to where they had started out, in this case, where they’d been caught.

And this is exactly what happened, as long as the locations simulated by the magnetic fields were within the sharks’ natural range.

Bearded man gesturing and explaining a structure inside a fabric greenhouse with a shark pool to the right.
Bryan Keller describing the experimental setup to create the magnetic field conditions of different geographic locations. Image (video screenshot) via Keller et al./ Current Biology.

Interestingly, the Earth’s magnetic field doesn’t only help with compass information, but also helps the animals map out their surroundings: They are able to collect spatial information on their surroundings relative to their location, and they are able to maintain the same heading. These two pieces of information combined make it possible for them to migrate to their target locations.

Bottom line: Using bonnethead sharks, researchers have shown that sharks rely on Earth’s magnetic field to map their surroundings and navigate long distances as they migrate.

Source: Map-like use of Earth’s magnetic field in sharks

Via Scitech Daily

Via AAAS Science

May 13, 2021

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