Sharks Use Earth's Magnetic Field Like a Compass, Enabling Them to Travel Over 12,000 Miles

Scientists have believed for a long time that these animals depend on magnetic sensing to travel across oceans. At last, someone puzzled out how to prove it. Great white sharks travel more than 12,000 miles yearly from South Africa to Australia, charting a closely ideal straight line across the ocean. And each year, they turn around and migrate back.

Earth's Magnetic Field

There are no street signposts to lead them and, for most of the journey, no fixed landmarks by which they can set their route. There is usually a change in currents and water temperatures. The sunsets at night, the stars vanish during the day. But the sharks still carry on with their movement.

Experts for decades have made speculations that sharks must be making use of the Earth's magnetic field as a kind of atlas, but it was difficult to prove due to the fact that sharks are generally hard to study. It's difficult to keep them in captivity, and some species are huge, for instance, a great white - stretches up to about 20 feet long and can weigh more than 2,000 pounds.

Theory of Shark's Magnetic Navigation

It's difficult to make an experiment massive enough to study them in a controlled laboratory environment. Currently, in a study out today in Current Biology, a group of experts describes how they did it. In order to test the long-held sharks' magnetic navigation theory, a researcher at the Florida State University Coastal and Marine Laboratory, Bryan Keller, built an apparatus that could copy specific magnetic fields. He built a 10-foot wooden cube that has a large tank in the middle.

Then he curved over a mile of copper wiring around the cube at specified intervals. The copper passed on electrical current and produced a magnetic field when connected to power. By making some adjustments to the power, Keller could produce either a stronger or weaker field, imitating specific conditions the sharks might meet in the ocean.

The Navigators

If the sharks gave themselves orientation in a certain way on the basis of the strength and angle of the magnetic field, that would be proof that they were making use of that information to understand their location on the planet and to puzzle out which direction to swim. This approach has been applied in studying other animals, such as sea turtles.

And the study's lead author, Keller, says that experts are already aware that sharks have the ability to detect magnetic fields. But, he says, "this is the first occasion where it's revealed that they make use of that ability to infer location." Still, there was a limitation. The magnetic field of the cube was not big enough to track the movements of known navigators like the great white. Keller said in order to study these animals with this approach, they required a shark that was not big but was still migratory.

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