The antennae-like whiskers of harbor seals exist for a good reason, and researchers have just confirmed that these whiskers play a good role in detecting prey and navigating the marine creatures' way with striking precision.
Earlier studies noted trained seals' ability to chase an object's path even when blindfolded. Now a new study from engineers at the Massachusetts Institute of Technology (MIT) found that this "laser-like tracking ability" can be attributed to their whiskers.
The researchers created and tested a large-scale model of a harbor seal's whisker, and learned that such bodily features serve two main purposes: keeping steady following a seal's own water movement, and oscillating in a "slaloming" motion in response to the turbulence a moving object produces.
The study was written by MIT mechanical engineering professor Michael Triantafyllou and former graduate student Heather Beem, who published their findings in the Journal of Fluid Mechanics. Beem's Ph.D. thesis was the basis for the work.
Once the experimental whisker entered the wake left by a passing object, it began vibrating at the same frequency as the passing vortices of the wake. The whisker slalomed among these vortices and resembled "a skier zigzagging between flags." The slaloming then allowed the whisker to vibrate at the wake's precise frequency and give the seal clues to the object's size, shape, and path.
Many marine animals such as whales and dolphins use echolocation, an internal sonar system allowing them to locate objects based on reflected sound. This study, however, pointed exactly to the slaloming action of whiskers for the same ability in seals.
According to Triantafyllou, bio-inspired sensors modeled after the animals' whiskers may assist underwater vehicles in tracking schools of fish and pollution sources.
"By having several whiskers on a vehicle, like the seal, you can, for example, detect a faraway plume, and track it all the way to the end," he said.
The researchers also suggested that the unique shape of the harbor seal's whiskers - wavy to the naked eye and more intricate under a magnifying glass - may contribute to the creature's outstanding sensitivity. Triantafyllou said it is a perfect sinusoid instead of a straight antenna.
The whisker's morphology is believed to have a quieting effect that helps seals block out their own disturbance as they tread the water, as if being able "to stick your head out of a car window, and have there be no noise, so that your ears don't ring."
Mitra Hartmann, a Northwestern University professor who was involved in the study but has done research on whiskers, said that whiskers appear to be designed for purposes ranging "from texture sensing to shape discrimination." For example, rats use their smooth whiskers to detect the texture of things much like how human use their fingertips.
Photo: Chuck Abbe | Flickr
