The impact of piscivorous predators on fish populations in Austrian waters.

Fish populations in Austrian rivers have declined sharply in recent decades due to hydromorphological degradation, energy-related development and climate change. Meanwhile, the impact of fish-eating predators on these already stressed communities is a hotly debated topic. The project aims to quantify the additional predation pressure while taking ecological conditions into account. To this end, historical and current fish stock data on abundance, biomass and population structure, collected since the return of predators, are analysed and examined by water body type and degree of stress, in order to separate the effects of predation from those of habitat and climate factors. In parallel, cross-state data on the occurrence and population trends of predators are compiled and used for relative trend analyses. Using distribution and feeding ecology data, we estimate the consumed fish biomass and spatiotemporal predation pressure, linking them to fish stock trends. The analysis is conducted across scales, from the national level down to the level of selected case study rivers. The results will provide a scientific basis for managing fish-eating predators in the context of protecting and sustainably using Austrian river fish stocks.