Post-LIFE-Monitoring Fischökologie: Erhebung des fischökologischen Zustands in den Befischungsstrecken des LIFE-Projekts Naturschutzstrategien für Wald und Wildfluss im Gesäuse

In the course of the post-LIFE monitoring, electrofishing was carried out in two stretches of water in the Enns in order to assess the effectiveness of the river construction measures implemented in the LIFE project Forest and Wild River in the Gesäuse using the fish stock data. These upgrading measures were intended to improve fish ecological conditions, which deteriorated considerably in the course of the 1990s. In the investigation section between the Paltenspitz and the Geäuse Entrance, eleven fish species were caught, with the lead species grayling, brown trout and koppe being the most common fish species. The resulting fish population comprises 260 individuals per hectare and a hectare biomass of only 14.164 kg. Although extensive water-ecological enhancement measures have been implemented in the area of the Paltenspitze, the poor fish-ecological status is present in the investigation section upstream of the Gesäuses. This is mainly due to the lack of relevant model species and the extremely low biomass. Compared to the fish ecological surveys carried out under the LIFE project Forest and Wild River in the Gesäuse, the fish stock in this section of the Enns continues to decline. It must therefore be concluded from the current situation that the aquatic ecological upgrading measures have been carried out on too small a scale in order to bring about a noticeable improvement in the deficient fish ecological situation of the hard-regulated Enns section upstream of the Gesäus. The second examination route is located in the Gesäuse National Park, which extends from the Gofergraben to the Johnsbach estuary. In the course of electric fishing, seven species of fish were caught, with the lead species grayling, brown trout and koppe once again dominating. The calculated fish population is 260 individuals per hectare, with a hectare biomass of 20.193 kg. Due to the low biomass, the Gesäuse National Park is also in poor fish ecological condition. The restructuring of the Johnsbach estuary as part of the LIFE project is to be seen as a successful upgrading measure. The lower course of the Johnsbach is a suitable growing habitat for young lads and is therefore partly responsible for the positive development of the grayling population in the examination section in the Gesäuse. In order to permanently improve the fish ecological conditions in the study area, a comprehensive remediation of the Enns is required, whereby the most far-reaching restoration of a natural water morphology and the reduction of anthropogenic influence are to be seen as the most important steps.