How seal whiskers master underwater hunters

Harbor seals have about 100 whiskers, but they’re not just for looks. They provide animals with important information about their surroundings.

“These are sensory hairs in the facial area,” says Yvonne Kruger, a biologist at the University of Rostock in Germany. “And these whiskers can be used to sense water movement caused by the fish.”

That’s because their movements leave marks in the water, where the seals can find and eat the fish. “When you look at a plane, you see it leaves a trail,” Krueger says by analogy. “And this is similar to when a fish is swimming through the water column. You can’t see it, but you can feel it with your whiskers.”

Seals can use their whiskers to extract all kinds of information from turbulence in the water. They can determine the direction something moved. Laboratory studies suggest that seals may even be able to distinguish between the movements of different types of fish.

Krueger’s research suggests that harbor seal whiskers may help them outwit the evasive behavior of the fish they hunt.

suspicious escape

In one experiment, Journal of Experimental BiologyKrueger focused on the feats of an adult male harbor seal named Filloo. He is dark gray and lives in a marine science center in Germany. “He’s so beautiful,” Krueger says.

“We have a very strong bond,” she added. “Filu likes to do everything right. He likes learning new things. He gets irritated if he gets even one thing wrong.”

In short: “He’s a nerd,” she says with a smile.

Krueger trained Firou to test a practical theory that seals use their whiskers to outwit fleeing fish.

Harbor seals are talented predators, but it’s hard work. After all, fish don’t want to be eaten. Let’s try rainbow trout, a favorite food of harbor seals.

“Rainbow trout can hide their direction of swimming by making a C-shape,” Krueger says. “Then it just swims off in a different direction.” [than] They have swam before. ”

This new posture and evasive swimming behavior causes the trout to rotate the two vortex rings in the water in opposite directions. Think of it like a smoke ring made of water. And only one of those rings (the slightly smaller one) moves in the direction the fish swims, potentially confusing the pursuing harbor seal.

Krueger wanted to know whether harbor seals could read camouflage and track fish, since both vortex rings point the seal in different directions. One is almost parallel to the swimming fish, and the other is almost opposite.

She thought that if seals like Firou could distinguish between the sizes of vortex rings, they might be able to learn and follow the correct vortex ring. Philoo did not disappoint.

Get results from your training

Krueger spent almost two years training Firou to choose the larger of two artificially created vortex rings underwater. “You have to be patient with animals,” she says. “You have to give them time to learn.”

Eventually, Filloo figured it out and was able to tell the rings apart even when the size difference was smaller than the width of a human thumb, much smaller than what would need to be identified in the wild.

“This shows that filu can successfully hunt rainbow trout and follow the right direction to prey on them,” Krueger says.

And when she covered Firou’s beard with nylon stockings, he could no longer complete the task. This suggests that it was his whiskers that were giving him the information he needed to distinguish between the two vortex rings.

Although this is just one animal, Krueger and his colleagues say they think it’s an ability that harbor seals likely share more commonly, and one that could very well be demonstrated in the wild.

“If you think about harbor seals swimming in the ocean and foraging, they can actually read where the fish have been and where they’re going,” she says. “So if you’re hunting in murky water or hunting at night, you don’t need to see the fish.”

Robin Grant, a sensory biologist at Manchester Metropolitan University, said the study was a “hugely important step in understanding how seals behave”. [use] Their whiskers are used to extract small pieces of information from these hydrodynamic signatures. ”

“It would have been nice to have information about the exact movement of the whiskers,” says Grant, who was not involved in the study. “But this is a great start telling us what they can do.”

Grant said understanding how animals like harbor seals perceive their surroundings is valuable because it can reveal how they are affected by changes in their environment, such as extreme weather events.

“You can imagine that that might mask some of the important stimuli that the seals want to sense,” she says.

Additionally, Grant observes that these discoveries could stimulate sensors that could help underwater robots navigate their surroundings to perform tasks related to underwater archaeology, mining, and biological exploration.

In other words, Firou appears to be forging his own path that others may eagerly follow.