杏吧原创

Cameras attached to blue whales have inadvertently revealed new information about the behaviour of 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 the whales to minimise drag.

鈥淣o one else has looked to see what remoras are doing before,鈥� says Brooke Flammang at the New Jersey Institute of Technology.

There are eight species of remora fish. Each fish has a suction disc that it uses to cling to larger animals such as whales. The disc is on the on the top of the remora鈥檚 head, so it clings upside down to sharks, manta rays and other rays.

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

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

鈥淲e were happy to have all these photobombing remoras,鈥� she says. Her team鈥檚 analysis of the footage shows that remoras鈥� favourite spots on blue whales are behind the blowhole, behind the dorsal fin and around the pectoral fins.

A supercomputer analysis of fluid flow around blue whales confirmed there is much less drag in these places, making it easier for the remoras to stay attached. Yet their suction discs are strong enough for them to cling on in places where drag is much higher, the team calculated. Indeed, the videos show they do sometimes attach to places such as the tail flukes where drag is very high.

The footage also reveals that remoras move around whales with ease, skimming just above their surface. The faster-flowing water in the thin layer between the fish and whale 鈥渟ucks鈥� the remora towards the whales, ensuring they don鈥檛 become detached, says Flammang.

Goldbogen could also benefit from Flammang and her colleagues鈥� work. The suction cups he has used to attach cameras to whales seldom remain attached for more than two days, but Flammang鈥檚 team has developed an artificial version of the remora suction disc that should stay attached for weeks.