{"id":6454,"date":"2015-10-26T04:39:30","date_gmt":"2015-10-26T04:39:30","guid":{"rendered":"http:\/\/revoscience.com\/en\/?p=6454"},"modified":"2015-10-26T04:39:30","modified_gmt":"2015-10-26T04:39:30","slug":"study-finds-a-whiskers-slaloming-motion-helps-seals-track-and-chase-prey","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/study-finds-a-whiskers-slaloming-motion-helps-seals-track-and-chase-prey\/","title":{"rendered":"Study finds a whisker\u2019s \u201cslaloming\u201d motion helps seals track and chase prey"},"content":{"rendered":"

\"MIT-Whisker-Slalom_0\"<\/a>CAMBRIDGE, Mass. —\u00a0Harbor seals have an amazingly fine-tuned sense for detecting prey, as marine biologists have noted for years. Even when blindfolded, trained seals are able to chase the precise path of an object that swam by 30 seconds earlier. Scientists have suspected that the seal\u2019s laser-like tracking ability is due in part to its antennae-like whiskers.<\/p>\n

Now engineers at MIT have fabricated and tested a large-scale model of a harbor seal\u2019s whisker, and identified a mechanism that may explain how seals sense their environment and track their prey.<\/p>\n

The team found that a seal\u2019s whiskers serve two main functions in sensing the environment: first remaining still in response to a seal\u2019s own movements through the water, and then oscillating in a \u201cslaloming\u201d motion in response to the turbulence left by a moving object.<\/p>\n

[pullquote]The research shows that this slaloming allows the whisker to extract energy from the wake, causing it to vibrate at the precise frequency of the wake\u00a0[\/pullquote]<\/p>\n

In their experiments, the researchers observed that once the fabricated whisker enters the wake left by a passing object, it starts vibrating at the same frequency as the wake\u2019s passing vortices. Careful visualizations show that the whisker \u201cslaloms\u201d among the vortices, like a skier zigzagging between flags.<\/p>\n

The research shows that this slaloming allows the whisker to extract energy from the wake, causing it to vibrate at the precise frequency of the wake \u2014 a mechanism that may give seals a clue to an object\u2019s path, its size, and even its shape.<\/p>\n

Michael Triantafyllou, the William I. Koch Professor in MIT\u2019s Department of Mechanical Engineering, says that biologically inspired sensors, modeled after the harbor seal\u2019s whiskers, may aid underwater vehicles in tracking schools of fish, as well as sources of pollution \u2014 a goal that he is currently working toward.<\/p>\n

He and former graduate student Heather Beem, whose PhD thesis formed the basis of the work, have published their results in the\u00a0Journal of Fluid Mechanics.<\/em><\/p>\n

A \u201cquieting effect\u201d<\/strong><\/p>\n

The harbor seal\u2019s whiskers are unique in shape: Even to the naked eye, an individual whisker appears not uniform, but wavy. Under a magnifying glass, the pattern is more intricate, with an elliptical cross-section that varies in size along its span.<\/p>\n

\u201cIt\u2019s marvelous to see this intricate pattern, it\u2019s not just a straight antenna \u2014 it\u2019s a perfect sinusoid,\u201d Triantafyllou says.<\/p>\n

He and Beem proposed that a whisker\u2019s curiously geometric morphology may play a part in a seal\u2019s exceptional sensitivity.<\/p>\n

Using 3-D printing techniques, Beem reproduced the seal\u2019s wavy morphology at a much larger scale, in order to accurately measure its response to various wakes. She tested the whisker\u2019s vibration properties in a 30-meter-long tank of water with a moving track suspended above the water.<\/p>\n

In her experiments, Beem first attached the artificial whisker to the moving track, allowing the whisker to freely vibrate in the water as it moved down the length of the tank.<\/p>\n

While most long, thin rods tend to create large vortices, or eddies, as they move through water, forming a pattern that\u2019s well-known in fluid mechanics, Beem found that the wavy pattern of the whisker\u2019s geometry created much weaker vortices, enabling the whisker to move silently, with very little vibration, through the water.<\/p>\n

The whisker\u2019s morphology, the researchers found, may help the seal block out its own disturbance as it moves through water.<\/p>\n

\u201cIt\u2019s like having the ability to stick your head out of a car window, and have there be no noise, so that your ears don\u2019t ring: It\u2019s a quieting effect,\u201d Triantafyllou says.<\/p>\n