Fish-ecological monitoring at the Alte Donau in 2019/2020

Net fishing in the previous years of investigation (to check the condition factors of the most common fish species of the Alte Donau) resulted in reduced catches despite increased fishing effort. However, simultaneous electrofishing could not confirm a decrease in abundances. Nevertheless, discussions with the local managers indicate that the typical fish species in open water are no longer found in particularly high stocks. The reasons for this may be many, but cannot be clearly identified at present. In order to continue the long-term data series, the condition factors will again be determined using net equipment in the 2019/2020 monitoring. At the same time, the abundances of typical Alte Donau fish species will continue to be observed, thus monitoring the condition of the overall ecosystem. Regardless of the condition factors - but still in view of the declining abundances - net fishing will also be carried out from spring 2020, when the spawning season begins. These will be carried out in parallel with the investigation of fish eggs from the cuttings. The collected fish eggs will be analysed by means of metabarcoding in order to draw conclusions on the species diversity. This helps to understand which fish species are particularly endangered by the mowing process in their choice of spawning substrate. Using presence/absence data, affected fish species can be recorded. Parallel net fishing will support the metabarcoding data collected.