Why Seals Twitch Their Whiskers
Many mammals have whiskers that help them perceive their surroundings. The sensory experience may include subtle detection of vibrations, such as the way elephant trunk whiskers pick up mechanical signals when they brush against other objects. Aquatic mammals may also sport whiskers, although they encounter a much more liquid environment.
Seals in particular have extraordinary abilities to find prey in total darkness. Thanks to their ultra-sensitive whiskers, they are known to follow the hydrodynamic traces left behind when fish and other potential pieces of seafood swim by. The bases of their whiskers have enormous concentrations of nerves, more than 10 times greater than those that would be found in the whiskers of a land animal. When seals hunt their prey, they have been observed moving their whiskers back and forth in a “whip” motion, the function of which is a mystery that engineering and technology researchers at the University of Groningen in the Netherlands attempted to solve in a recent study.
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Using soft actuators to mimic the performance of the muscles at the base of seal whiskers, the researchers moved a real seal whisker back and forth in a fluid medium. Specifically, the researchers modeled the whiskers of harbor seals and, according to Ph.D. Chinmay Gupta and other study authors achieved an angle of 17 percent with water moving at 0.5 meters per second, which is a typical swimming speed for seals.
The results showed that when the seal’s whiskers were pushed forward, they became more sensitive to hydrodynamic vibrations; this, however, required energy consumption on the part of the “muscles”. When the whiskers were moved back, they became less sensitive to the vibrations of the water but gave the muscles a chance to relax and recover. Essentially, back-and-forth whipping movements balance a trade-off between sensory detection of prey tracks and energy expenditure.
Additionally, when researchers constructed a bionic seal nose featuring 60 harbor seal whiskers, the snout performed rhythmic whipping and dynamic changes in the angle of the whiskers, which could motivate new robot designs for underwater sensing. For example, imagine a remote-controlled vehicle that has sensitive whiskers attached to it to help it navigate through the pitch darkness of the deepest parts of the ocean or the cloudiest depths of a lake.
All thanks, of course, to the simple movement of a harbor seal’s whiskers. 
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Main image: TashaBubo / Adobe Stock
