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Suckerfish use fast-flowing water to surf across swimming whales’ skin

Remoras attached to a blue whale’s dorsal fin

Minden Pictures/Alamy

Cameras attached to blue whales have inadvertently revealed the behaviour of the remora fish that hitch a ride on larger marine animals. Among other things, the footage shows that remoras move around much more than was thought, skimming along just above the skin of whales to minimise drag.

“No one else has looked to see what remoras are doing before,” says Brooke Flammang at the New Jersey Institute of Technology.

There are eight species of remora fish, which have suction discs that they use to cling to larger animals such as whales. The disc is on the on the top of their head, so the remoras cling up on upside down to sharks, mantas and rays.

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The remoras let go when they see a chance to feed, grab the food and then reattach. They also eat skin parasites on their hosts.

This lifestyle makes them really hard to study. But at a conference in 2015, Flammang saw Jeremy Goldbogen of Stanford University present videos obtained by attaching cameras to blue whales with suckers. He joked that he had advertently captured hundreds of hours of remora footage – exactly what Flammang wanted.

“We were happy to have all these photobombing remoras,” she says. Her team’s analysis of the footage shows that remoras’ favourite spots on blue whales are behind the blowhole, behind the small dorsal fin and around the pectoral.

A supercomputer analysis of fluid flow around blue whales confirmed that the remoras prefer these places because there’s much less drag, making it easier for them to stay attached. But their suction discs are strong enough for them to cling on in places where drag is much higher, the team calculated, and indeed the footage shows they do sometime attach to places such as the tail flukes where drag is very high.

The footage also shows that remoras move around whales with ease, skimming just above the surface. The faster-flowing water in the thin layer between the fish and whale “sucks” the remora toward the whales, ensuring they don’t become detached, says Flammang.

Flammang’s work should also benefit Goldbogen. The suction cups he uses to attach cameras to whales seldom remain attached for more than two days. Her team has developed an artificial version of the remora suction disc that should stay attached for weeks.

Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.226654

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