Sea turtles are known for relying on magnetic signatures to find their way across thousands of miles to the very beaches where they hatched.

Now, researchers reporting in the journal Current Biology on May 6, 2021, have some of the first solid evidence that sharks also rely on magnetic fields for their long-distance forays across the sea.

“This research supports the theory that they use the earth’s magnetic field to help them find their way; it’s nature’s GPS.”.

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.

The question then was whether bonnetheads managed those return trips by relying on a magnetic map.

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.

The researchers suggest that this ability to navigate based on magnetic fields may also contribute to the population structure of sharks.

This figure shows how the experiment assessed the ability of bonnethead sharks to use the Earth’s magnetic field to navigate.

In future studies, Keller says he’d like to explore the effects of magnetic fields from anthropogenic sources such as submarine cables on sharks.

They’d also like to study whether and how sharks rely of magnetic cues not just during long-distance migration but also during their everyday behavior.

Reference: “Map-like use of Earth’s magnetic field in sharks” by Bryan A.

May 5, 2021