Assessing the impact of climate change on brown trout ( Salmo trutta fario ) recruitment

Climate change influences air temperature and precipitation, and as a direct consequence, the annual discharge pattern in rivers will change as climate warming continues. This has an impact on bedload transport and consequently on aquatic life, because coarse sediments in streams provide important habitat for many species. Salmonids, for example, spawn in gravel, and during their early life stages live in or on top of the substrate. We used a multiple model approach to assess how predicted discharge changes affect bedload transport and the vulnerable early life stages of brown trout (Salmo trutta fario) in a prealpine catchment in Switzerland. In the study area, future discharge scenarios predict an increased frequency of flood occurrence in winter and long-lasting low-flow periods in summer. As a result, bed erosion will become more frequent during winter, leading to less stable spawning grounds and deeper scouring, but during summer, an improvement in habitat diversity can be expected, which is advantageous for young-of-the-year fish. To face the future challenges of climate change, we recommend widening of riverbeds and improvements in longitudinal connectivity.