Sharks use Earth’s magnetic field as ‘GPS’ guidance system, study says
Scientists in Florida have concluded that sharks possess an internal navigation system similar to GPS that allows them to use Earth’s magnetic forces to travel long distances with accuracy.
The researchers from Florida State University made the discovery by subjecting 20 bonnethead sharks, part of the hammerhead family, to “magnetic displacement” exercises that replicated geographical locations hundreds of miles from where they were captured.
When the sharks were exposed to magnetic cues emulating a site about 375 miles south of where they were captured, they turned to swim north, exhibiting a “homeward orientation” suggesting the use of magnetic forces in their navigation, said Bryan Keller, the lead author of the study.
The research published in the scientific journal Current Biology helps explain why sharks can travel across vast oceans but return to exactly the same location annually to feed, breed and give birth, Keller said.
“We’ve known for some time they have the ability to detect the magnetic field, this is the first time that’s tested successfully that they use those abilities to infer their location or if they’re garnering map-like information from the magnetic field,” he said.
“We expect these abilities are also observed in other species like the great white to migrate 20,000km out and back to the same spot.”
Keller and his team believe the bonnetheads’ “onboard” navigation system is probably common to other species of sharks because it is unlikely bonnetheads evolved with sensitivity to magnetic forces while others that also travel long distances did not.
The team captured the juvenile bonnetheads in St George Sound off the Florida panhandle and placed them in a room-sized pool surrounded by copper wire. This allowed researchers to simulate magnetic cues from the capture site and from positions roughly 375 miles north and south.
In the southerly case, the sharks responded uniformly with “homeward orientation”, suggesting they can “differentiate geographic locations using map information from the geomagnetic field”, the study said.
From the capture site simulation, the sharks swam in random directions, and from the north the sharks appeared disorientated. Sharks rarely migrate north. Keller said it was likely because “they’ve never been up there”.
“It wasn’t a dramatic effect,” he said. “We tracked their behavior with a camera and we used software to track their sleep patterns and analyse the statistics. We learned that the mean average angle of the shark was towards their capture area, to their summer residence.”
According to Science Magazine, in 2005 a great white shark was tracked swimming from South Africa to Australia and back again in almost a straight line, leading scientists to believe sharks have a magnetic sense to steer themselves similar to those found in sea birds, lobsters and turtles.
Until now, however, little research has been conducted.
“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,” biophysicist Michael Winklhofer of Germany’s University of Oldenburg told Science.
Other experts said the Florida team’s findings were “compelling” but said more research was necessary before an internal GPS system in sharks is proven.
“The question has always been, even if sharks are sensitive to magnetic orientation, do they use this sense to navigate in the oceans, and how?” Robert Hueter, a retired senior scientist at Mote marine laboratory on Florida’s west coast, told the Associated Press.
“These authors have made some progress at chipping away at this question.”