Analysis of the swimming behavioral response of western blacknose dace in a turbulence modified flow field
Goettel, Michael Thomas
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Fish passage success rates through hydraulic infrastructure have been historically low due to flow field conditions that exceed the physical or behavioral capabilities of a given species. Significant efforts to design and modify hydraulic structures for enhanced passage rates have failed to achieve the desired results, with a primary reason being a poor understanding of how fish respond to complex hydraulic conditions. Many contemporary research efforts have targeted the inter-relationship between hydraulics and fish behavior in the laboratory using live fish trials in an attempt to better comprehend these interactions and ultimately provide a basis for the development of biologically-based design criteria. In this study experiments were conducted to assess the behavioral responses along swimming trajectories of western blacknose dace ( Rhinichthys obtusus ) in turbulent flow conditions. The objective was to test the hypothesis that the dace would preferentially adjust their swim paths to minimize their exposure to elevated turbulent conditions. Experimental data were collected through digital imaging of dace trajectories for fish that had been released into a shallow flume and allowed to swim through turbulence enhanced flow fields. Additionally, detailed velocity measurements were collected with an acoustic Doppler velocimeter to allow the comparison of dace trajectories to flow field conditions represented by average metrics of turbulent kinetic energy and Reynolds shear stresses. Analysis of the data consisted of the quantification of the proportion of the time that a dace's swim path selected a direction toward a lower magnitude turbulence condition when such an option existed. Fish paths were also graphically compared to turbulence contour plots to qualitatively assess the presence of swim path preferences or patterns. Lastly, video footage of each trial was evaluated to qualitatively assess the presence of novel behaviors that could have implications for the swimming trajectories observed. Results indicate that the dace did not preferentially avoid turbulence at statistically significant levels under the conditions experienced in the flume; however, data do suggest that some behavior relative to turbulence was non-random. Qualitative observations of video footage suggest that non-hydraulic factors, such as the presence of conspecifics and light intensity, also influence the swim path trajectories of the western blacknose dace. Future research will require more targeted turbulent conditions, simultaneous multivariate observations and analyses that factor in non-hydraulically-based behavior and the incorporation of coupled behavioral and hydraulic data at reduced time and length scales for primary variables. It is envisioned that the results of this study can provide guidance for future studies aimed at developing biologically based design criteria for enhanced fish passage at hydraulic infrastructure.