How remora 'sucker fish' use physics to surf on their whale hosts

Originally published on October 31, 2020.

New research has uncovered how remora — also known as suckerfish — are able to swim freely across the surface of a blue whale without getting knocked off by fast-moving water.

Remora are common marine hitchhikers. They use a fleshy disc on the top of their heads to latch on to whales, sharks, and even ships as they go through the ocean, snacking on parasites and dead skin along the way.

After seeing footage of remoras riding a blue whale, biologist Brooke Flammang noticed that they weren't always attached to their host, and instead, would surf across the whale's skin, even as the massive mammals moved quickly through the water.

"I was just mesmerized by the idea that they weren't having to work that hard, and they just seemed to be sort of floating and hovering around the whale body," Flammang told Quirks & Quarks host Bob McDonald.

This led to a multi-year, collaborative research effort to understand the fluid dynamics around a blue whale. The team ultimately discovered that remoras keep from being swept off their host by sliding inside a slow-moving cushion of water that flows around the whale as it swims.

The research was recently published in the Journal of Experimental Biology. 

Supercomputer reveals 84 per cent reduction in drag

Flammang, an Assistant Professor in the department of biology at the New Jersey Institute of Technology, said that studying remoras in the wild can be a challenge.

"One of the biggest things about studying remoras is that no one's really done it before. People have mostly only been interested in the charismatic megafauna to which the remoras are attached," said Flammang.

In 2015, Flammang saw the footage of blue whale-riding remoras, captured with suction-cup-mounted cameras on whales, by Stanford University marine biologist Jeremy Goldbogen. For the first time, it gave her the opportunity to see the remoras in action in the wild.

"Even when [the whales] were swimming very fast, the remora didn't need to stay attached the whole time; they went about their usual behaviour where they would dislodge from the surface and move about the body of the whale."

After teaming up with Goldbogen and other researchers to sift through the footage, they studied live remoras and built a 3D mathematical model of a blue whale. However, the computers they had access to weren't powerful enough to do the necessary calculations. Ultimately, they turned to the Barcelona Supercomputer Centre in Spain to figure out the remora's secrets. 

"We needed much stronger computing power to get down to the level of resolution that we wanted, which was sort of millimetres around the flow of a gigantic organism," she said. 

In doing this, the team found a "boundary layer" of water around the whale, several centimetres thick — a kind of liquid halo of water that moved with the massive mammal. The remoras stayed within this halo, where they experienced an 84 per cent reduction in drag compared to moving in open water at the same speed. This made it much easier to stay with their whale host.

"It really is its own little planet as far as the remoras are concerned. It's their own little world there," said Flammang.

Bio-inspired suction cups — now with less drag

The 3D model also showed that the places where remora tended to congregate — behind the blowhole, behind and next to the dorsal fin, and above and behind the pectoral fin — were the places that had the least amount of drag.

"If you're really familiar with fluid dynamics, these things are not surprising because there's a hump-type surface. And so then the flow has to react around that hump. So that sort of emphasizes the area of low drag in those areas," she said.

Now, she wants to use this knowledge to build remora-inspired suction cup devices to enable researchers to get even better videos of marine animals in the future. The cameras used by Goldbogen stayed on the blue whales for about 24 hours, but with this knowledge, Flammang said, they can try to develop technology that can stay on much longer.

"We currently don't have any sort of man-made devices that can adhere underwater without having to glue or suction cup to the surfaces. And so we are looking for something that can stick to surfaces for a reasonably long time, where you can get a month's worth of data collected without harming the animal." 

Produced and written by Amanda Buckiewicz.