Noisy waters.

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In this Issue, Popper & Hawkins (2019) provide “An overview of fish bioacoustics and the impacts of anthropogenic (human-made) sounds on fishes.” For fishes, hearing provides extremely important information about their environment, including information about events at distances well beyond those detectable by other senses. Moreover, acoustic cues in the underwater soundscape play an essential role in communication, predator–prey interactions, orientation and migration. The authors point out that the term ‘noise’ refers to unwanted sounds that are judged unpleasant, loud or disruptive to hearing and/or behaviour. Since the industrial revolution, human-generated noise has increased substantially in aquatic habitats. Activities such as shipping, sonar, pile driving, dredging, etc. may all have important negative impacts on fish populations and communities. The review begins with an overview of basic elements of underwater sound and the major sources of underwater noise. It proceeds to consider the biology of hearing and acoustics for fishes. It then reviews how anthropogenic sound could potentially affect fishes, noting that sound rarely causes mortality, but that biologically important effects can include temporary hearing impairment, masking the detection of biologically important sounds, physiological changes including stress, and changes in behaviour. The authors point out that there are numerous gaps in our knowledge of potential effects of anthropogenic sound on fishes and that much research is needed in order to fill the gaps and allow much better understanding of potential anthropogenic effects. The authors take the view that experiments performed in enclosed spaces such as tanks do not provide very useful information about how fishes will respond to anthropogenic noise in the wild. They suggest this because the sound fields presented in tanks and confined spaces are quite unlike what fishes would experience in natural aquatic settings and because animals may behave differently when not confined. The reader should be aware that these viewpoints are not shared by all researchers working on effects of noise on fishes. The review also considers existing criteria and guidelines regarding regulation of exposure of fishes to sound, with a particular emphasis on Europe and the United States. Given the absence of information on sound sensitivity for a vast majority of species, the authors suggest that classification of fishes based upon their auditory apparatus is a useful means of generalising across species. The review concludes with research directions and recommendations, specifically on the need to select representative species and to focus upon behavioural responses, the fact that fish hearing is mostly sensitive to particle motion rather than sound pressure, and how to scale up effects to understand implications for populations. The authors mention that “Further research is required on the responses of a range of fish species to different sound sources, under different conditions. There is a need both to examine the immediate effects of sound exposure and the longer-term effects, in terms of fitness and likely impacts upon populations.”