  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.
