A biologically based measure of turbulence intensity for predicting fish passage behaviours

Abstract

Many fishways were designed to facilitate upstream migration at anthropogenic barriers for targeted species, such as salmonids, though these designs may impede the passage of non-target species with different swimming capabilities. Developing passage metrics that quantify hydraulic conditions scaled to biological behaviours or traits could identify the causes of challenging passage conditions and aid design of multi-species fishways. Our objective was to test the performance of six velocity- and turbulence-derived metrics for predicting passage behaviours of Pacific Lamprey (Entosphenus tridentatus) under varying hydraulic conditions within an experimental vertical slot. These metrics were the 1) swim path-averaged water velocity, 2) swim path-averaged turbulence kinetic energy ( TKE ¯ ), 3) power, 4) work, 5) a biological turbulence intensity, I ¯ Bio , quantified as the ratio between the root of the TKE ¯ and a biological criterion (the bulk average velocity for which lampreys shift from free-swimming to attachment behaviours, UBio = 1.8 m·s−1) and 6) a flow index I ¯ Bio , which is I ¯ Bio modulated by a dimensionless velocity U* = U/UBio , where U is the mean flow through the vertical slot. We assessed the performance of these metrics by evaluating their relationship with Pacific Lamprey attachment time, which serves as an important behavioural proxy for passage difficulty. Only I ¯ Bio and F were significantly associated with attachment time and we suggest these metrics can be adapted for other fish species based on velocity thresholds inducing key behavioural responses. More broadly, our study demonstrates the importance of accounting for turbulence and employing biological criteria when quantifying fish passage within or across species.