Abstract
Although it is known that seals can use their whiskers (vibrissae) to extract relevant information from complex underwater flow fields, the underlying functioning of the system and the signals received by the sensors are poorly understood. Here we show that the vibrations of seal whiskers may provide information about hydrodynamic events and enable the sophisticated wake-tracking abilities of these animals. We developed a miniature accelerometer tag to study seal whisker movement in situ. We tested the ability of the tag to measure vibration in excised whiskers in a flume in response to laminar flow and disturbed flow. We then trained a seal to wear the tag and follow an underwater hydrodynamic trail to measure the whisker signals available to the seal. The results showed that whiskers vibrated at frequencies of 100–300 Hz, with a dynamic response. These measurements are the first to capture the incoming signals received by the vibrissae of a live seal and show that there are prominent signals at frequencies where the seal tactogram shows good sensitivity. Tapping into the mechanoreceptive interface between the animal and the environment may help to decipher the functional basis of this extraordinary hydrodynamic detection ability.
Highlights
We recently reported that harbor seals are sensitive to mechanical vibrations from 10 Hz to 1,000 Hz10 – a range that extends much higher than the frequency content of hydrodynamic signals produced by swimming organisms
When a hydrodynamic disturbance from a cylinder with a shedding frequency of 4.2 Hz was placed upstream, the vibrational signal spanned a broader range of frequencies
While the addition of a hydrodynamic disturbance caused the vibrations on the whisker to markedly shift from a narrowband to a broadband signal, it did not significantly change the overall energy of the whisker signal (p = 0.43)
Summary
The accelerometer tag successfully recorded vibrations received from the supraorbital vibrissae of a freely swimming seal (Figs 3, S1–3). The broad range of frequencies over which the whiskers vibrate in disturbed flow fields may explain why seals have detection abilities that extend beyond the low frequency region associated with biological hydrodynamic signals[5, 11]. This is the first reported attempt to record and measure the sensory cues received by the whiskers of a live seal. Because the capability of the seal’s vibrissal system to detect and characterize hydrodynamic signals exceeds that of currently available technology[12], examining the function of this sensory system in freely swimming animals can aid the development of biomimetic systems
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