Determination of the vibration sensitivity of harbour seal (Phoca vitulina) vibrissae

Abstract

Psychophysical techniques were employed to measure the sensitivity of the vibrissae of a harbour seal (Phoca vitulina) to sinusoidal vibrations ranging between 100 and 2500 hertz. A control test ensured that the seal was not responding to auditory or other extraneous components of the signal. Vibration detection thresholds were found to decrease with increased frequency up to 1000 hertz and remain relatively constant thereafter. These data were used for evaluation of some previous hypotheses of vibrissae function. Calculations revealed that seals should be able to use their vibrissae to detect objects such as swimming fish vibrating underwater at close range and tactually discriminate between objects (like fish with different scale patterns). Also, vibrissae could theoretically detect underwater sounds produced by fish, but at too close a range to have any practical value.