Seals and sea lions often hunt fish in waters too dark or turbid to rely on eyesight. Instead, they follow their whiskers, using the turbulence generated by a fish’s wake. The vortices shed by the fish cause the seal’s whiskers to vibrate, giving them sensory information. To better understand what a seal can derive from this, a recent experiment looked at what a thin whisker can pick up from an upstream cylinder.
As expected, the strength of the whisker’s vibration fell off the farther away the cylinder was. But the researchers found that, if they moved the cylinder quickly — like a fish trying to dart away — the vibration of the whisker was stronger. They also found that the whisker was sensitive to misalignment. If the cylinder was placed ahead and to the side of the whisker, the whisker would still vibrate but would do so around a different equilibrium position. That result implies that a seal can get information both about the fish’s speed and direction, simply from the twitch of its whiskers. (Image credit: seal – K. Luke, illustration – P. Gong et al.; research credit: P. Gong et al.; via APS Physics)
