What do harbor seals and downhill skiers have in common?
An unexpected similarity between nature’s mechanisms and man’s techniques arise in a new study published in Journal of Fluid Mechanics. The paper reveals how harbor seals can detect prey from far away, and it’s related to skiing.
Around a decade ago, marine biologists began measuring the harbor seal’s uncanny ability to track objects several seconds after they had swum by. The “footprints” behind the object served as markers. Even if the seals were blindfolded, they could pick up on the markers by using their whiskers. What physical mechanism could be driving this phenomenon?
Heather Beem, then-graduate student in Mechanical & Oceanographic Engineering, and her PI, Prof. Michael Triantafyllou, designed a model experiment of a seal whisker encountering such “footprints”. In the MIT Towing Tank, she mounted a circular cylinder, which generated a vortex wake, similar to what a swimming fish creates in the water. She fabricated a plastic whisker-like sensor and towed it in the cylinder’s wake.
These experiments revealed an exquisite sensitivity of the whisker to detect the presence of the wake. As soon as the whisker hit the wake, it synchronized its motion to the periodic pattern of the swirling vortices. Flow visualizations displayed the whisker to slalom perfectly back-and-forth through the vortices, extracting energy to power large vibrations in the whisker. These wake-induced vibrations would clearly indicate to the seal that it was in the trail of the fish.
Just as a racing skier zig-zags between gates, harbor seal whiskers slalom between vortices, leading the seal straight to the source of its dinner.
MIT Mechanical Engineering’s YouTube Channel:
This paper is freely available for 30 days via the following link: journals.cambridge.org/flm/beem
Photo credit: Heather Beem