Discovering salmonids with Remote Underwater Video (RUV) technology, a winter pilot study in a Small Alpine Stream

Freshwater ecosystems are currently facing a biodiversity crisis. The decline in freshwater fish populations, particularly in alpine streams, is exacerbated by environmental changes such as climate change, habitat fragmentation, and human activities. In this context, monitoring freshwater fish populations is complex, especially in winter conditions with snow cover when traditional methods, such as electrofishing, become difficult. This pilot study explores the use of remote underwater video (RUV) systems for monitoring salmonids in winter conditions in the Torrente Vallanta, an alpine stream in North-West Italy. By using 28 deployments and a total effort of 8.97 hours, our results demonstrate that RUV technology is effective for detecting the presence of salmonids, estimating the size and observing their behaviour in remote streams. The detectability of salmonids varied across different segments of the stream and RUV technology provided valuable insights into winter fish behaviour, such as limited movement and the search for hideouts. This study sets the foundation for future research on fish assemblages in poorly studied streams in the Alps, providing an important tool for conservation efforts in the context of the freshwater biodiversity crisis.