Sensing Fish at a Distance
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• Physics 16, s46
The whiskers of some marine mammals are delicate to the turbulent wakes left by fish. A brand new experiment investigates how this course of works over totally different distances.
Martina Berg/inventory.adobe.com
In turbid coastal waters the place visibility is poor, harbor seals observe their prey utilizing their whiskers. These lengthy, stiff hairs are delicate to the turbulent forces produced by close by fish. Most efforts to grasp this sensing have centered on conditions wherein the hunter is immediately downstream of its prey, following at a hard and fast distance. Now Pengyao Gong and colleagues on the College of Texas at Dallas have experimentally studied the phenomenon for various distances and orientations between the 2 animals [1].
When a fish strikes by way of water, it sheds vortices from its pores and skin, which produce a turbulent wake behind the fish. These vortices are identified to induce so-called wake-induced vibration (WIV) within the whiskers of a pursuing seal.
Gong and colleagues studied this phenomenon experimentally. They changed the fish with a vertical cylinder, which they drove by way of the water horizontally, and the whisker with a a lot thinner rod that was fastened at one finish. Most often, the group discovered that the energy of the WIV fell because the cylinder–whisker distance elevated. However after they moved the cylinder away very quickly—an experiment meant to duplicate a sudden burst in a fish’s velocity—this WIV falloff slowed due to the stronger wake vortices generated by the cylinder’s quicker movement.
The group additionally discovered that the whisker oscillations had been delicate to the relative positions of the whisker and the wake: when the 2 had been misaligned, the wake nonetheless induced whisker vibrations, however the vibrations’ equilibrium place was totally different. The researchers say that their outcomes present that the movement of a seal’s whiskers might present the animal with a wealth of details about its prey’s velocity and course.
–Marric Stephens
Marric Stephens is a Corresponding Editor for Physics Journal primarily based in Bristol, UK.
References
- P. Gong et al., “Coupling between vortex circulate and whisker sensor in cylinder wakes with time-varying streamwise gaps,” Phys. Rev. Fluids 8, 034701 (2023).
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