Sharks use the Earth’s magnetic field to find the correct one. Researchers think it may be a learned behavior.
Some sharks are true long-distance swimmers. Plus, they almost always seem to find the right person. That way, for example, the great white shark could swim all the way from South Africa to Australia, more or less in a straight line.
Scientists have long suspected that Earth’s magnetic field had something to do with it. However, evidence was lacking, but US researchers have now coiled copper wires around a larger “cage” with a smaller swimming pool in the middle. When the electric current was connected through the copper wires, a common magnetic field was created inside the pool.
Before that, researchers collected about 20 hammerhead sharks with shovels, a species known to migrate hundreds of kilometers off the coast of Florida in the United States.
The sharks were placed in the pool one by one, while the researchers created three different magnetic fields that were randomly arranged. One field simulated the Earth’s magnetic field at the same spot where the sharks were caught, while the other two simulated the magnetic field 600 kilometers north and south of the capture site, respectively.
When the magnetic field was the same at the capture site, the sharks swam in random directions. When the magnetic field simulated it south of the capture site, the sharks swam to the north side of the pond, thinking they were on their way home.
But when sharks were placed in the northern magnetic field, something happened that surprised the researchers. Then they seemed helpless and swam again around some holes around the noise in the pool.
The reason may be that a hammerhead shark with a spade head does not usually migrate north of the capture site, says one of the researchers behind the study, Brian Keeler of Florida State University, to Science News:
It can support the theory that their ability to direct themselves is a learned behavior. They probably don’t know what to do when they’re in the northern field, because they’ve never been there before.
However, the current study, published in Current Biology, does not provide an answer for how sharks sense changes in Earth’s magnetic field. There is still a bit of a mystery. Some researchers believe that the ability depends on cells that contain a magnetic mineral, magnetite, while others believe that a special protein in the retina, cryptochrome, may have something to do with it.