A hydrodynamics-based framework to evaluate the impact of fishways on drifting lake sturgeon larvae

Abstract

Lake sturgeon (Acipenser fulvescens) have recently been a target for conservation in the Laurentian Great Lakes. While improving spawning success has been a major goal of these efforts, an often-overlooked component is the survival of the larvae after hatching, during the period of downstream drift. In a dammed river system, during this phase, larvae may need to drift past dam infrastructure. This journey past dams often results in an increase in larval mortality for a variety of reasons, including exposure to highly turbulent flow. Quantifying the aspects of turbulence related to larval mortality within fishways will inform retrofitting or future design efforts of fishways to improve larval viability. This study uses dimensional arguments to characterize the flow conditions influencing larval viability through fishways. One such condition discussed here is strain rate, which can be used as a diagnostic basis to determine candidate fishways for conservation measures. Based on Kolmogorov’s theory (1941), the strain rate present in the fishway at the pertinent scale for lake sturgeon larvae, Sη, can be estimated using the fishway’s macroscale Reynolds number Re, the relevant macroscale fishway velocity U, and the smallest fishway pool dimension le as Sηle/U ≈ Re1/2. This approach is illustrated in the case of the Vianney-Legendre Fishway in Québec, and determined this fishway to be potentially hazardous to drifting lake sturgeon larvae.