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May 7, 2021 08:50 pm

Sharks Use Earth's Magnetic Field To Navigate the Seas

A new study suggests some sharks can read Earth's field like a map and use it to navigate the open seas. ScienceMag: The result adds sharks to the long list of animals -- including birds, sea turtles, and lobsters -- that navigate with a mysterious magnetic sense. "It's great that they've finally done this magnetic field study on sharks," says Michael Winklhofer, a biophysicist at the Carl von Ossietzky University of Oldenburg in Germany, who was not involved in the study. In 2005, scientists reported that a great white shark swam from South Africa to Australia and back again in nearly a straight line -- a feat that led some scientists to propose the animals relied on a magnetic sense to steer themselves. And since at least the 1970s, researchers have suspected that the elasmobranchsâ"a group of fish containing sharks, rays, skates, and sawfish -- can detect magnetic fields. But no one had shown that sharks use the fields to locate themselves or navigate, partly because the animals aren't so easy to work with, Winklhofer says. "It's one thing if you have a small lobster, or a baby sea turtle, but when you work with sharks, you have to upscale everything." Bryan Keller, an ecologist at Florida State University, and his colleagues decided to do just that. The researchers lined a bedroom-size cage with copper wire and placed a small swimming pool in the center of the cage. By running an electrical current through the wiring, they could generate a custom magnetic field in the center of the pool. The team then collected 20 juvenile bonnethead sharks -- a species known to migrate hundreds of kilometers -- from a shoal off the Florida coast. They placed the sharks into the pool, one at a time, and let them swim freely under three different magnetic fields, applied in random succession. One field mimicked Earth's natural field at the spot where the sharks were collected, whereas the others mimicked the fields at locations 600 kilometers north and 600 kilometers south of their homes. When the applied field was the same as at the collection site, the researchers found that the animals swam in random directions. But when subjected to the southern magnetic field, the sharks persistently changed their headings to swim north into the pool's wall, toward home, the researchers report today in Current Biology

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