Creating underwater vision through wavy whiskers: a review of the flow-sensing mechanisms and biomimetic potential of seal whiskers

Abstract

Seals are known to use their highly sensitive whiskers to precisely follow the hydrodynamic trail left behind by prey. Studies estimate that a seal can track a herring that is swimming as far as 180 m away, indicating an incredible detection apparatus on a par with the echolocation system of dolphins and porpoises. This remarkable sensing capability is enabled by the unique undulating structural morphology of the whisker that suppresses vortex-induced vibrations (VIVs) and thus increases the signal-to-noise ratio of the flow-sensing whiskers. In other words, the whiskers vibrate minimally owing to the seal's swimming motion, eliminating most of the self-induced noise and making them ultrasensitive to the vortices in the wake of escaping prey. Because of this impressive ability, the seal whisker has attracted much attention in the scientific community, encompassing multiple fields of sensory biology, fluid mechanics, biomimetic flow sensing and soft robotics. This article presents a comprehensive review of the seal whisker literature, covering the behavioural experiments on real seals, VIV suppression capabilities enabled by the undulating geometry, wake vortex-sensing mechanisms, morphology and material properties and finally engineering applications inspired by the shape and functionality of seal whiskers. Promising directions for future research are proposed.

Whiskers as hydrodynamic prey sensors in foraging seals

“…Further, protracted whiskers may also detect smaller water movements, such as the breathing currents of fish (24), enabling seals to capture immobile fish without bioluminescence (30). The elephant seal foraging strategy of persistent swimming is made possible by the adaptations seen in their vibrissal system: well-innervated, highly sensitive whiskers (14) with an undulated surface structure that suppresses selfgenerated flow noise (10)(11)(12). Such anatomical and morphological advantages are important factors, in addition to their extreme physiological diving ability (3), that enable elephant seals to forage in the deep, dark ocean.…”

“…They followed the hydrodynamic trails behind moving objects that passed by at an earlier point up to several tens of seconds in time and 40 m in distance (8,9). Also, the morphology of phocid whiskers includes a unique undulated surface structure that suppresses vibrations generated while swimming, increasing the signal-to-noise ratio (10)(11)(12). Finally, phocid vibrissae can sense mechanical vibrations from 10 Hz to 1,000 Hz, a surprisingly high range that includes the frequency content of hydrodynamic signals produced by swimming organisms (11).…”

Bioinspired NEMS—Prospective of Collaboration with Nature

“…Biomimetics, to begin with [1][2][3], has a great potential for solving human problems by imitating the natural environment or learning from it. For example, an extensive review of bioinspired triboelectric nanogenerators includes a comparative analysis of structures and materials that draw inspiration from nature [4].…”

Natural Frequency Measurements of Seal Whiskers Using A 3D-Printed MEMS Graphene-Based Cantilever Sensor

“…Pinnipeds (seals, sea lions, and walruses), rats, cats, and otters have whiskers that can act as sensors to obtain essential information about the surrounding environment, thus playing a key role in natural organisms' survival from the points of view of both escaping from predators and catching prey [1]. Whiskers of certain seal species like grey and harbor seals have undulating surfaces, which look like beads on a string (Fig.…”

“…The seal whisker's VIV suppression capability has also inspired engineers to develop whisker-like sensors [3,[5][6][7] for marine flow sensing applications. It has also led to various engineering applications of whisker-like structures, such as building bases for oil platforms to decrease the force caused by the underwater vibrations [1]. The undulating whisker geometry ensures minimization of vortex-induced vibrations and frequency synchronization with that of the dominant wake frequency of the escaping prey [2].…”