Approach velocity and impingement duration influences the mortality of juvenile Golden Perch (Macquaria ambigua) at a fish exclusion screen

Globally, the extraction and diversion of water from river systems has had substantial impacts on aquatic ecosystem health and ecological processes. One such impact is the entrainment of fish at pump offtakes that can result in vast quantities of fish being permanently removed from rivers. Exclusion screens to prevent fish entrainment at pump offtakes are therefore an important management consideration. In this study, impingement and subsequent injury and mortality of a juvenile freshwater perciform, Golden Perch (Macquaria ambigua), was assessed in the laboratory using a simulated fish exclusion screen under a range of velocities and impingement durations. A 2 mm wedge-wire screen eliminated the entrainment of 44-day-old Golden Perch that were exposed to approach velocities between 0.05 and 0.3 m/s. However, impingement rates of Golden Perch increased significantly with increased approach velocities and rates of injury and mortality increased with impingement duration. Results from this study indicate the primary mechanisms to reduce fish loss at pump offtakes are to design pump offtakes, fitted with fish exclusion screens, which limit approach velocities or impingement duration. Further studies are required to examine a range of species with varying swimming ability at early life-history stages. Such data will contribute to the growing body of knowledge that supports adaptive management plans to prevent fish loss at water offtake pumps.