The role of freshwater bioacoustics in ecological research

Conventional methodologies used to estimate biodiversity in freshwater ecosystems can be nonselective and invasive, sometimes leading to capture and potential injury of vulnerable species. Therefore, interest in noninvasive surveying techniques is growing among freshwater ecologists. Passive acoustic monitoring, the noninvasive recording of environmental sounds, has been shown to effectively survey biota in terrestrial and marine ecosystems. However, knowledge of the sounds produced by freshwater species is relatively scarce. Furthermore, little is known about the representation of different freshwater taxonomic groups and habitat types within the literature. Here we present results of a systematic review of research literature on freshwater bioacoustics and identify promising areas of future research. The review showed that fish are the focal taxonomic group in 44% of published studies and were studied primarily in laboratory aquaria and lotic habitats. By contrast, lentic habitats and other taxonomic groups have received relatively little research interest. It is particularly striking that arthropods are only represented by 26% of studies, despite their significant contributions to freshwater soundscapes. This indicates a mismatch between the representation of taxonomic groups within the freshwater bioacoustic literature and their relative acoustic contribution to natural freshwater soundscapes. In addition, the review indicates an ongoing shift from behavioral studies, often with focus on a single taxonomic group, towards fieldbased studies using ecoacoustic approaches. On the basis of this review we suggest that future freshwater bioacoustics research should focus on passive acoustic monitoring and arthropod sound, which would likely yield novel insights into freshwater ecosystem function and condition.