Sharks Use the Earth’s Magnetic Field Like a Compass - WIRED

For decades, scientists have speculated that sharks must be using the Earth’s magnetic field as a sort of atlas, but it was hard to prove because sharks are notoriously difficult to study.

If the sharks oriented themselves in a certain way based on the strength and angle of the magnetic field, that would be an indication that they were using that information to understand their position on the planet and to figure out which direction to swim.

And Keller, the study’s lead author, says that scientists already knew that sharks are capable of detecting magnetic fields.

The cube’s magnetic field was much too small to track the movements of famous navigators like the great white.

One mimicked the angle and strength of the one they’d naturally encounter in their Florida home, one was like the field they’d encounter at a point 600 kilometers south along their normal migratory route, and another was like a point 600 kilometers north in Tennessee, a place where the sharks have never been.

But when they were exposed to the magnetic field like the one they’d find 600 kilometers south, they consistently oriented themselves with their heads pointing north.

“It’s a really interesting and clear demonstration that sharks are using the Earth’s magnetic field as a kind of map,” says Kenneth Lohmann, a professor of biology at the University of North Carolina who was not involved in the study.

He says this study suggests that the ability to navigate using magnetic sensing may be widespread among marine animals that migrate seasonally.

When they’re small, the sharks learn the magnetic “address” of their native estuary or bay.

Yet exactly how any animal senses magnetic fields remains “a real mystery,” says Lohmann.

Another is that magnetic fields affect receptors in their visual systems, superimposing colors or light patterns over their vision, like an augmented-reality headset.

Perhaps these receptors also sense magnetic fields, or pick up on them indirectly by noticing how they interact with electrical currents.

“It has really big implications for management and conservation of these species,” says Kyle Newton, a biologist at the University of Washington in Saint Louis, who studies how stingrays navigate using magnetic fields.

And just as Keller’s cube used power to mimic the Earth’s magnetic field, power cables underwater also create their own little magnetic fields in the ocean.

Since people can’t feel magnetic signals, says Newton, “it’s easy for us to overlook this stuff.