Speed Sensing in a Harbour Seal

Abstract

Many pinnipeds travel long distances between breeding and feeding grounds in some cases showing remarkable homing abilities (James & Dykes, 1978). Very little is known about the methods they use to plot their course but if they were aware of their rate of movement, this ability could conceivably assist them. The following procedure which was undertaken with a captive male harbour seal (Phoca vitulina Linnaeus) demonstrated that the animal was able to determine his swimming speed.The seal was first trained to swim at any speed through ten hoops 48 cm in diameter submerged at equal intervals around the periphery of an 8 m oval tank filled with sea water to a depth of 1.2 m. Each trial consisted of one circuit of the tank, and always began at the same hoop. A screen preventing the seal from going through this start hoop was removed to indicate the onset of each trial. The seal was then trained to swim the 17 m course maintaining a speed of 6 km/h. The experimenter observed from a bridge suspended over the tank, and measured the animal's speed by listening to a series of tones. These tones were audible only to the experimenter and were timed such that if the seal were swimming at 6 km/h, he would reach each hoop at the same moment the experimenter heard the tone. A buzzer was sounded whenever the animal swam at less than the required speed, and a whistle was blown if he were moving too quickly.

Passive wake detection using seal whisker-inspired sensing

“…[111] again showed pinnipeds able to locate objects in total darkness. Moreover, the harbor seals here were able to discriminate between two objects, which were visually identical but differed in acoustic impedance one airfilled ring and one water-filled ring (Figure 1-4a).…”

“…These active devices demand a significant portion of the vehicle's battery power. Experiments with real seals suggest that they may use their vibrissae to detect and maintain their speed [111]. A whiskerlike sensor, which is mechanical-based as in the real seals, could serve as a low-power, low-cost alternative to the standard devices in certain scenarios.…”

“…Perhaps they default to other sensory systems, as in [111], in which seals could maintain constant speed both with and without presence of its vibrissae. In that case, the seals may have used visual cues instead.…”

Sensory Biophysics of Marine Mammals

“…The ability of P. vitulina to swim through a series of hoops at constant speed both before and after its vibrissae had been clipped off was assessed by Renouf and Gaborko (1982). The removal of its vibrissae seemed to have no effect, but since the seal could see the hoops, the experiment did not disprove Montagna's (1967) suggestion that one function of the vibrissae might be to detect speed.…”

Wake induced by an undulating elephant seal whisker

“…Seals with whiskers (vibrissae) of undulating morphology, which are the majority of true seals (Phocids), can trace even minute disturbance caused by prey fish in the ambient flow using only sensory input from their whiskers (Dehnhardt and Kaminski 1995;James and Dykes 1978;Renouf and Gaborko 1982). The superior sensing capability of harbor seal whiskers is attributed to the suppression or augmentation of vortex induced vibration (VIV), generated by bluff-bodies in air or water flow paths.…”