Response of seaward-migrating European eel (Anguilla anguilla) to an infrasound deterrent

•An infrasound (12 Hz) source modified adult eel behaviour during seaward migration.•Eel exhibited longer and more erratic swim paths during operation.•Avoidance was insufficient to reduce overall passage rate at a water intake.•Infrasound may be beneficial in multimodal systems for eel behavioural guidance. Behavioural guidance technologies that employ stimuli to attract or repel fish offer potential to enhance, or even replace, costly physical and mechanical screens traditionally used to protect fish at river infrastructure such as hydropower and water intakes. At these structures, eel can suffer high rates of damage and mortality if entrained in pumps or turbines, or impinged on screens intended to protect them. This study used acoustic telemetry to quantify the behavioural response of adult European eel (Anguilla anguilla) to infrasound (12 Hz) under field settings. Eel (n = 50) were tracked after release immediately upstream of the forebay of a redundant hydropower facility. An infrasound deterrent located at the water intake either emitted continuously (ON) or was switched OFF. Treatment (ON/OFF) was alternated nightly over 10 consecutive nights with five eel released during a single trial conducted each night. Seventy eight percent of the 41 eel that moved downstream into the forebay passed the intake. Although the infrasound deterrent had no effect on passage rate, fine-scale differences in movement patterns were determined. When the infrasound was ON, eel trajectories were on average over twice as long with frequent erratic turns and milling behaviour (i.e. repeated lateral movements perpendicular to the principal flow direction), and they were less active within the intake channel close to the device. It is important to consider the influence of site characteristics, especially water velocities that dictate the potential for eel to respond to an acoustic field created. Infrasound deterrents that induce avoidance could be used to protect eel, either through enhancing the efficiency of physical screens or as part of multimodel behavioural guidance systems.