Document Type

Article

Journal/Book Title

Journal of Experimental Biology

Publisher

The Company of Biologists Ltd.

Publication Date

8-9-2024

Journal Article Version

Accepted Manuscript

Volume

227

Issue

15

First Page

1

Last Page

33

Abstract

Complex hydrodynamics abound in natural streams, yet the selective pressures these impose upon different size classes of fish are not well understood. Attached vortices are produced by relatively large objects that block freestream flow, which fish routinely utilize for flow refuging. To test how flow refuging and the potential harvesting of energy (as seen in Kármán gaiting) varies across size classes in rainbow trout (Oncorhynchus mykiss; fingerling, 8 cm; parr, 14 cm; adult, 21 cm; n = 4 per size class), we used a water flume (4,100 L; freestream flow at 65 cm s-1) and created vortices using 45° wing dams of varying size (small = 15 cm, medium = 31 cm, large = 48 cm). We monitored microhabitat selection and swimming kinematics of individual trout and measured the flow field in the wake of wing dams using time-resolved Particle Image Velocimetry (PIV). Trout of each size class preferentially swam in vortices rather than the freestream, but the capacity to flow refuge varied according to the ratio of vortex width to fish length (VW : FL). Consistent refuging behavior was exhibited when VW : FL > 1.5. All size classes exhibited increased wavelength and Strouhal number and decreased tail beat frequency within vortices compared with freestream, suggesting that swimming in vortices requires less power output. In 17% of the trials, fish preferentially swam in a manner that suggests energy harvesting from the shear layer. Our results can inform efforts toward riparian restoration and fishway design to improve salmonid conservation.

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