# Seal and Sea lion Whiskers Detect Slips of Vortices Similar as Rats Sense Textures

## TL;DR

This study models how pinniped whiskers detect vortex-induced slip events by analyzing their response to hydrodynamic trails, revealing a novel sensing mechanism based on the time derivative of whisker bending.

## Contribution

It provides the first theoretical and experimental insight into pinniped whisker interaction with vortex streets, highlighting the importance of the response derivative for efficient sensing.

## Key findings

- Whiskers respond with jerky, stick-slip motions to vortices.
- The time derivative of whisker response better decodes vortex frequency.
- The derivative of bending moment is identified as the optimal sensing variable.

## Abstract

Pinnipeds like seals and sea lions use their whiskers in hunting their prey in dark and turbid conditions. There is no theoretical model or a hypothesis to explain the interaction of whiskers with hydrodynamic fish trails. The present work provides insight into the mechanism behind the Strouhal frequency identification from a Von-Karman vortex street behind bluff bodies, similar to the inverted hydrodynamic fish trail. Flow over 3D printed sea lion head with integrated whiskers of similar geometrical and material properties was investigated when being exposed to vortex streets behind cylindrical bluff bodies. It is found that the whiskers respond to the vortices by a jerky motion similar to the stick-slip response of rat whiskers on different surface textures. The Strouhal frequency of the upstream wake is clearly decoded with the time-derivative of the whisker response rather than the displacement response, which increases the sensing efficiency in noisy environments. It is hypothesized from the work that the time derivative of the bending moment of the whiskers is the best physical variable, which can be used as the input to the neural system of the pinnipeds.