Fluids 16L39—L Instead, this more or less steady fundamental frequency should be modulated by a hydrodynamic event impinging on the hair, for example a vortex, and this modulation would be the crucial information for the sea lion. Besides the design of technical constructions with improved behaviour while exposed to fluid flow, sensory applications are a focus of further investigations of pinniped vibrissae. This study indicates that the different types of vibrissae of harbour seals and California sea lions use different mechanisms for the detection of external hydrodynamic information. Tests with cylinders of 4 and 8 mm diameter revealed equivalent results.
This procedure was used with seal whiskers.
Flow sensing by pinniped whiskers
Delayed stall due to leading edge tubercles of the humpback whale flipper. Whereas the majority of frequencies measured for harbour seal whiskers possess amplitudes below 3 mV, frequencies of sea lion whiskers reached values approximately 10 times higher figure 1 c. Considering that at this speed, the pliable vibrissae are protracted to the most forward position largely perpendicular to the swimming direction, it remained undefined how these animals are able to accurately analyse hydrodynamic events in front of them. Because of the high flow resistance resulting from their own locomotion, the vibrissal hair shaft was expected to be bent backwards and, additionally, to vibrate because of vortex shedding from the hair vortex-induced vibrations, VIV However, a recent study by Hanke et al. Figure 7 exemplifies an experiment where a harbour seal followed the hydrodynamic trail generated by a miniature submarine. The California sea lion Zalophus californianuswhich is the eared seal species best studied behaviourally to date, has 38 mystacial vibrissae on each side counted in 4 animals Dehnhardt,no rhinal vibrissae Ling,but supraorbital vibrissae, which are less prominent than in true seals pers. Psychophysical experiments have shown that all three groups of pinnipeds investigated in harbour seals as representatives of the true seals, California sea lions as representatives of the eared seals, and in the walrus can discriminate objects with high accuracy by direct touch with their vibrissae.