Quantifying fish response to extreme hydraulic conditions during downstream passage

Abstract

This paper describes an innovative metric to quantify fish response to extreme hydraulic conditions, in particular, high flow velocities and strong velocity gradients. Such conditions are typical for hydraulic conduits of turbines and pumps but also bypasses for downstream fish migration. The presented metric was developed within the project RETERO which main objective is to contribute to animal test free methods for assessing the risk of fish injury in passages of hydraulic structures. The swimming performance of fish in a pressurized laboratory flume have been video-recorded and evaluated, resulting in high temporal and spatial resolution animal position datasets. Proposed characteristics such as “movement mode”, “movement mode switch”, “normalized swim power”, “reaction start position” and “reaction strength” allow to comprehensively investigate animal behavior and link fish swimming performance to the thresholds of hydraulic parameters. The movement mode provides information about the body orientation and movement direction of the fish in relation to the experimental flume. The normalized swim power characterizes swimming activity in the current mode. Points of movement mode switches, reaction start positions and reaction strength allow to detect thresholds of environmental triggers such as velocity and spatial velocity gradient (SVG) on an objective basis. In the paper we demonstrate the application of described metrics for the selected number of experiments with brown trout under daylight and dark conditions. First evaluations show that thresholds of SVG referenced in the literature, which can trigger avoidance reactions, also hold for the passages with high flow velocities near sprint speed capacity.