The effects of turbulence on habitat selection and swimming kinematics of fishes.

摘要

This dissertation has investigated the role of turbulent eddies on habitat selection and swimming kinematics of fishes. First, the level of turbulent velocity fluctuations in habitat selected by brown trout (Salmo trutta) was investigated in the field. It was found that turbulent velocity fluctuations were lower in areas that fish selected compared to otherwise viable habitat based on standard habitat suitability indices. Based on the results from these field observations, a series of laboratory experiments tested the effects of turbulent eddies on fish swimming kinematics. Specifically, a series of increasing velocity tests were conducted such that creek chub (Semotilus atromaculatus, total length = 12.2 cm) were swum downstream from either a control grid or one of three cylinder arrays (diameters of 0.4, 1.6, and 8.9 cm, with gaps equal to cylinder diameter) which were oriented either vertically or horizontally. The control grid and cylinder arrays produced turbulent flow regimes with 95th percentile eddy diameters ranging from 1/6 to 1 fish length and 95th percentile eddy vorticity ranging from 1.5 to 11.3 s-1 across cross-sectionally averaged flow speeds ranging from 8.5 to 50.2 cm.s-1. As eddy diameter and vorticity increased (and hence eddy momentum), the fish critical swimming speed and tail beat frequency decreased. Conversely, increasing eddy momentum resulted in increased tail beat amplitude, spill rates, and pectoral and pelvic fin percentage area and time deployed. In the presence of eddies with high momentum the fish based Strouhal number was found to increase linearly with the fish based persistence parameter. Further, it was found that changes in the orientation of the eddies, which either rotated about horizontal or vertical axes, produced changes in critical swimming speed, spill rates, and the pectoral fin deployment pattern. It was shown that the primary mechanism which links the features of turbulence to the response of fish was the relative momentum of the eddies with respect to the fish. Finally, in order to apply the results from these laboratory experiments to the field, a portable, submersible, miniature particle image velocimetry device was developed and tested allowing for the collection of turbulent eddy metrics in fluvial environments.