Swimming Behavioural Responses and Impingement Risks of Larval Golden Perch to Fish Protection Screen Approach Velocities

Fish protection screens are increasingly being considered as management tools to prevent significant numbers of fish being extracted from Australian rivers at water diversions. Australian design standards specify an approach velocity (the perpendicular flow 8 cm in front of the screen) of 0.1 m.s −1 . This value was based on studies on juvenile fish, but the extent that it protects larval fish is understudied. The swimming of three ontogenetic stages of Golden perch larvae (protolarvae, postflexion and metalarvae) was observed in front of a screen in a variable speed swimming flume. Approach velocity and water temperature were varied, and the likelihood of impingement and the time for impingement to occur was measured. Swimming behaviours employed by fish to avoid impingement were also quantified. Protolarvae were the most susceptible, with almost 100% impingement at all tested velocities. Impingement became less likely as larvae increased in age. However, at velocities above 0.10 m.s −1 impingement likelihood increased for all stages. The results indicate that if an approach velocity of 0.10 m.s −1 is adhered to, that a critical time of 10 s is available in which larvae may be protected. Larvae implemented key behaviours to avoid impingement, which changed as they developed morphologically. Protolarvae displayed use of hydraulic refuging behaviours, whilst postflexion and metalarvae used a burst and coast strategy. Those that did not implement these behaviours became impinged. Current Australian specifications for fish protection screen design can therefore facilitate the protection of larval Golden perch. Protection improves significantly as larvae develop beyond the protolarval stage.