Sounding out the river: an end-to-end framework for monitoring bioacoustic events and sediment movement in freshwater soundscapes

Hadrien Helfgott, Matthew Gervais, Emma Halliwell, Mark Naylor

Despite rivers’ cornerstone place in global biodiversity and the key ecosystem services they provide to human societies, their soundscapes are severely understudied. Three challenges are in part responsible for this gap: the active nature of rivers complicates deployment logistics, their structural noise hinders the detection of significant events, and occuring sounds are largely under-characterised and unattributed to specific species. Here, we present a hardware set-up designed for long-term underwater river monitoring, and a computational framework to identify and analyse the highly diverse events that occur in this still largely unexplored acoustic environment. Our low-cost/low-power hydrophone recording solution is comprised of a portable weighted hydrophone mount and a separate land-based audio recording unit, well-suited to flexible deployment in freshwater streams and rivers. Our software protocol then allows us to detect and analyse stand-out events of geomorphic or biological nature despite the major background noise variations that naturally occur in fluvial settings. Applying this method on the River Ness allows us to monitor sediment movements across environmental conditions, and to detect significant bioacoustic signals including salmonid redd-cutting, water surface events, and bird vocalisations. Further application of the framework proposed in this paper will allow for continuous monitoring of rivers across Scotland, a clearer grasp of both sedimentary and biological events happening in underwater soundscapes, and a stronger understanding of their interactions.