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article imageShape of whiskers make seals experts at finding, catching fish

By Megan Hamilton     Oct 18, 2015 in Environment
Boston - Recent research shows that the reason seals are such effective hunters is due to the unique shape of their whiskers.
Protruding from an animal's cheeks, whiskers can help them feel touch; something that's important since most mammals don't have hands.
Whiskers also help mammals detect movement, texture, and to maintain their balance, UPI reports.
For seals, however, their whiskers are extremely important and very precise. A new study, published in the Journal of Fluid Mechanics shows that it's the unusual, wavy shape of a seal's whiskers that makes them so effective.
As a fish swims, its movements disturb the water, and if a seal is nearby, the frequencies of the disturbance causes the marine mammal's whiskers to vibrate at the same pace. Amazingly, the vibrations are then translated by the seal's brain, revealing the passing prey's size, shape, and trajectory.
For years, marine biologists noticed that harbor seals (Phoca vitulina) were really fine-tuned for detecting prey, Science Daily reports. They are so fine-tuned, in fact, that even when blindfolded, they can detect and chase the precise path of an object that swished by 30 seconds earlier.
In order to gain a better understanding of how harbor seals did this, engineers at The Massachusetts Institute of Technology (MIT) fabricated and tested a large-scale model of a harbor seal's whisker. This allowed them to identify a mechanism which may explain how seals sense their environment and track dinner.
A seal's whiskers serve two functions in detecting the environment, the researchers found. First, the whiskers remain still in response to the seal moving through the water, then they oscillate in a "slaloming" motion in response to turbulence caused by a moving object.
That's where the wavy whiskers come in handy.
"This shape enhances their ability to detect flows created by fish," the study's author, Heather Beem told Popular Science.
Their wavy whiskers are unique, Beem said. She studied the whiskers while a graduate student at MIT. Only a few seal species have them, and they aren't found on sea lions or walruses.
When Beem built the over-sized plastic model of one of these whiskers, she submerged it at one end of a large tank of water and pushed it forward to simulate a seal's whisker gliding forward as the animal swam. This gave her an idea of how a whisker's shape responds to ripples.
If a harbor seal's whiskers were smooth, moving through water would cause them to flap crazily, like a car antenna dancing and jiggling in the wind. The reason for this is that fluid flowing over a smooth object forms whirlpools. And the vortex of a whirlpool would tug on a smooth whisker, making it wiggle, Popular Science notes.
As the researchers learned from the experiments, wavy whiskers don't have this problem.
"The waviness breaks up the water flowing over it," Beem said. That's how a harbor seal's whisker can stay steady while the animal is swimming.
Then the researchers wanted to find out how a seal detects prey moving through the water, so the team subjected the whiskers to different frequencies of vibration in the water, The Washington Post reports.
They also added a simulated fish at the other end of the tank, in the form of a large cylinder that moved forward ahead of the plastic whisker, Popular Science reports. Whirlpools streamed in a regular rhythm as this pseudo-fish moved through the water and struck the fake whisker. As expected, the wavy whisker moved back and forth in time with the ripples.
The researchers think this is how the seal is able to determine the size, shape, and trajectory of the object. Since the whiskers vibrate based only on external stimuli, this gives a seal precision and stealth, the Post reports.
"The geometry of the whisker allows for this phenomenon of being able to move very silently through the water if the water's calm, and extract energy from the fish's wake in order to vibrate a lot," said Beem, in a statement. She began the study as part of her PhD, which she's now completed. "Now we have an idea of how it's possible that seals can find fish that they can't see."
Buoyed by this experiment, Beem has now built a basic whisker sensor for detecting water flow. She hopes one day to see it mounted on an aquatic robotic device designed to track migrating schools of fish, or to perhaps track the flow patterns created when chemical spills occur, Popular Science notes.
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