Research

The grayling (Thymallus thymallus) and rainbow trout (Onchorhynchus mykiss), which are key species for the fishing industry, show strong population fluctuations and sometimes unsatisfactorily low stocks in large parts of the Ybbs. In particular, a decline in the grayling population in the middle reaches of the river documented in 2024 and the noticeable decline in rainbow trout raise questions about the causes responsible. The proposed project aims to explain population demographic developments using abiotic descriptors – specifically flow and water temperature. The focus here is on the critical phase of incubation and emergence, a period that has been shown to be of great relevance for the further population development of salmonids (Unfer et al., 2011, Pinter et al., 2025). An additional focus is on the development of cohorts (year classes), i.e. the survival of individual age stages from year to year. The data available for the Ybbs is ideal for these analyses, as in addition to continuous hydrological data, there is a complete seven-year data series (2019–2025) of fish stock data from a district upstream of Amstetten – a unique data basis in the hyporhithral zone that enables well-founded and detailed analyses of reproductive success and cohort development. As part of the interpretation, influencing factors such as water morphology and potential stressors such as predation pressure and interspecies competition should not be ignored. By considering seamless population development, a new basis for future fisheries management steps and considerations is created. This redefines the prerequisites for sustainable and forward-looking management and lays the foundation for further considerations on current problems in fisheries management (status of the huchen population, consequences of climate change, etc.). Such research results are of great importance for this key species in the grayling region, especially in view of the unstable stocks of grayling, which is classified as vulnerable (Wolfram & Mikschi, 2007).

As part of the Joint Danube Survey 5 (JDS5), an extended environmental DNA (eDNA) survey will be conducted to assess biodiversity and ecological conditions along the Danube River. The project includes fish metabarcoding, ddPCR, macrophyte analysis, eRNA sampling, sentinel site monitoring, and the establishment of an eDNA archive. These molecular methods offer a comprehensive, integrative approach to riverine biomonitoring.The project is implemented in close cooperation with the Horizon Europe projects Danube4all and Danube Lifelines, supporting the advancement of innovative tools for large-scale aquatic ecosystem monitoring and restoration.

In the project "Water, Agriculture and Habitats", the options for rewetting wetlands are analyzed, taking into account ecological, social and economic aspects. For the test area "Pannonian Region", the aim is to process historical information that will subsequently be available as input for possible solutions and recommendations for action at regional level or for concrete rewetting and adaptation measures in test farms. In close cooperation with Land&Forst Betriebe Österreich and the Umweltdachverband, the Institute of Hydrobiology and Water Management at BOKU will scientifically investigate the historical situation with regard to wetlands in the study area "Pannonian Region" as part of work package 4 "Analysis of the initial situation". The focus is primarily on the analysis and characterisation of historical wetlands in the study area and the analysis of historical forms of use of these wetlands. The results are presented in the form of a report and a presentation.