Most animals migrate for food or for mating reasons using their internal compass or mental maps. Birds, bees, lobsters and sea turtles have been found to use electromagnetic waves to navigate and sharks have been suspected to do same.
A great white shark swam from South Africa to Australia and then back to South Africa in an almost straight line in the year 2005 making scientists propose it was with the use of magnetic fields.
Bonnethead sharks are known to be one of the smaller sharks that return to the same estuaries every year. This is why Bryan Keller, the project leader of Save Our Seas Foundation and his fellow researchers found the bonnetheads suitable for testing if sharks rely on electromagnetic signatures for navigation.
It was suspected sharks could sense electromagnetic fields as far back as the 1970's but no concrete research had been done to find out if they indeed navigate with these fields. According to Michael Winklhofer, a biophysicist at Carl von Ossietzky University of Oldenburg, Germany, no one could show sharks use these fields because you have to upscale everything due to their size.
Bryan Keller and his team collected 20 baby bonnethead sharks from a shoal off the Florida Coast, placing them one by one in a pool. The pool had been placed inside a lined copper wire cage and a custom magnetic field could be generated at the center of the pool when an electric current ran through the wiring of the cage.
Three different magnetic fields were simulated, one was that of earth's magnetic field and the others were 600km South and 600km North of the sharks' homes. The researchers found out that the sharks swam in random direction when a magnetic field similar to their collection site was applied. When placed in a southern magnetic field, the sharks swam northwards (home) towards the pool's wall suggesting that they use electromagnetic fields for long distance migration.
When subjected to the northern magnetic field, the sharks didn't favour a particular direction and Keller suggests this is because bonnetheads don't normally migrate North of their home and thus, it was uncharted territory.
Keller also says that other sharks like the great white sharks that travel even longer distances probably use the earth's electromagnetic field to do so. He looks forward to studying the effects of magnetic fields from anthropogenic origin on sharks. The team would also like to study if and how sharks rely on magnetic fields for their everyday use and not just for long distance movements.
Journal reference- Map-like use of Earth’s magnetic field in sharks. Current Biology, 2021; DOI: 10.1016/j.cub.2021.03.103