Configuration of multiple human stressors and their impacts on fish assemblages in Alpine river basins of Austria

Abstract This work addresses multiple human stressorsand their impacts on fish assemblages of the Drava and Murarivers in southern Austria. The impacts of single and multiple human stressorson riverine fish assemblages in these basins were disentangled, based on an extensive dataset. Stressorconfiguration, i.e. various metrics of multiple stressorsbelonging to stressorgroups hydrology, morphology, connectivity and water quality were investigated for the first time at river basin scale in Austria. As biological response variables, the Fish Index Austria (FIA) and its related single as well as the WFD biological- and total state were investigated. Stressor- response analysisshows divergent results, but a general trend of decreasing ecological integrity with increasing number of stressorsand maximum stressoris observed. Fish metrics based on age structure, fish region index and biological status responded best to single stressorsand/or their combinations. The knowledge gained in this work provides a basis for advanced investigations in Alpine river basins and beyond, supports WFD implementation and helps prioritizing further actions towards multi- stressorrestoration- and management.