Watch hammerhead sharks swim in 'cyclones' around ancient volcano in rare footage

Hundreds of hammerhead sharks gather around an ancient volcano in the Pacific Ocean, drawn by secret signals radiating from the seabed, a new clip reveals.

The footage, which features in the third episode of Netflix's new wildlife documentary series "Our Living World," shows a school of hammerhead sharks (Sphyrnidae) circling Cocos Island — a volcanic island in the eastern tropical Pacific about 310 miles (500 kilometers) southwest of mainland Costa Rica.

Cocos Island is a known haven for endangered hammerhead sharks, but scientists still aren't sure how and why so many sharks navigate across swathes of ocean to convene there every year.

"We don't really know how these sharks are doing this," Ben Roy, the series producer of Our Living World, told Live Science. "We know that they've got sensors in their heads and we know that these sensors pick up on the magnetic signature of these cool volcanic rocks."

The island formed when lava erupted from an ancient underwater volcano and solidified, until it eventually rose 12,000 feet (3,660 meters) above the seabed.

For the episode, film crews followed a young female hammerhead shark as she left her coastal nursery and traveled 300 miles (480 km) across the Pacific Ocean to the volcanic oasis, where scientists think the sharks assemble to relax, socialize and find a mate. The female instinctively knew the way to Cocos Island thanks to electromagnetic signals emanating from hardened volcanic rocks on the island's slopes.

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