Sharks navigate using Earth’s magnetic field

Sharks use a "magnetic map" for long-distance navigation...

Salmon and sea turtles have been shown to use the Earth’s magnetic field to find their way around, and now new research suggests that sharks also make use of a "magnetic map" to navigate.

“We know that sharks can detect different components of the magnetic field, but what we haven’t known until now is if they use that ability to infer locations. What we showed is that they use this ability to gather map-like information from the magnetic field,” explains Florida State University's Bryan Keller, who lead the new study published in Current Biology.

Previously, researchers knew that sharks travel back and forth across the world's oceans, returning to specific locations each time. “It’s a remarkable feat, navigating across an ocean basin without a cell phone, without a map, or at least a map in the way that we think of it,” says Keller.

But what we didn’t know was whether they remember the routes, or have some sort of "inbuilt GPS".

To discover how sharks navigate during these long-distance travels, Keller and his colleagues caught 20 juvenile bonnethead sharks. This is a small coastal species belonging to the hammerhead shark family that migrates and returns to the same locations every year.

The bonnethead sharks were placed in a tank wrapped in copper wire. By varying the current flowing through the wires, Keller altered the magnetic field in the shark tank to simulate three different locations: where the sharks were caught, a point along their migratory route 600 km south, and a land-locked site 600 km north where the sharks had never been.

If sharks are using Earth’s magnetic field to navigate, they would point themselves towards "home" when exposed to the magnetic field 600 km south of where they were caught, and react randomly to the other two locations. And that is exactly what they did.

“The only difference was the magnetic signatures or the magnetic fields available to the sharks; so we know that they are using the magnetic fields to help orient them towards their target,” Keller explains.

In the future, the team plan to investigate more deeply how sharks use magnetic fields. “The next steps are better understanding how sharks use this magnetic map, and how they use the Earth’s magnetic field for fine-scale movement."