Use of sound to guide the movement of eels and other fishes within rivers: a critical review

Downstream movements of some freshwater fishes, including eels, are adversely affected by the presence of hydroelectric structures and other anthropic factors. It is important to consider ways of influencing the movements of such fishes to ensure that their populations are protected and their abundance not detrimentally affected. It is especially important to divert migrating fishes to locations where they can be safely moved downstream. Guidance through exposure to underwater sound may effectively attract or deter fish in order to influence their movement to avoid in-water hazards and improve survival during downstream migration. This paper examines the available literature on the use of sound to control the movements of fishes, with an emphasis on pre-reproductive anguillid eels whose populations have been declining and which also must survive downstream passage in order to continue towards the spawning grounds in the Sargasso Sea. Information is provided on underwater acoustics, the detection of sounds by fishes, their responses to sound, the use of sound to guide fishes, and the generation of guiding underwater sounds. Information gaps are considered, and the paper explores the need to develop guidance systems that use acoustic cues, and perhaps other stimuli, to influence the behaviour of fishes. It is concluded that while it is premature to implement a full-scale acoustic guidance system to affect fish behaviour, with additional research it may be possible to develop acoustic and/or multisensory systems that could affect fish behaviour. It is also concluded that efforts to develop acoustic control systems have numerous advantages over other stimuli that do not propagate as well under widely diverse environmental conditions.