Post-LIFE Monitoring Fish Ecology: Survey of the fish-ecological status in the fishing routes of the LIFE project Nature Conservation Strategies for Forest and Wild River in the Gesäuse

In the course of the post-LIFE monitoring, electrofishing was carried out in two stretches of the Enns waterway in order to assess the effectiveness of the river-building measures implemented in the LIFE project Forest and Wild River in the Gesäuse using the fish stock data. These revaluation measures should lead to an improvement in the fish ecological conditions, which deteriorated sharply during the 1990s. Eleven species of fish were caught in the investigation route between the Paltenspitz and the Geäuse entrance, with the guide species grayling, brook trout and Koppe being the most common species of fish. The resulting fish stock comprises 260 individuals per hectare and a hectare biomass of only 14.164 kg. Although extensive water eco-revaluation measures have been implemented in the Paltenspitze area, there is a poor fish-ecological condition in the area of the palten peak. This is due to the lack of relevant model types and the extremely low biomass. Compared to the fish ecological surveys of the LIFE Forest and Wild River in the Gesäuse project, the fish population in this section of the Enns continues to decline. It must therefore be concluded from the current situation that the water eco-revaluation measures have been carried out too small-scale in order to bring about a noticeable improvement in the deficient fish-ecological situation of the hard-regulated Enns section. The second examination route is located in the Gesäuse National Park, which extends from the Gofergraben to the Johnsbach estuary. In the course of electrofishing, seven species of fish were caught, with the guiding species of grayling, brook trout and coppe again dominated. The calculated fish population is 260 individuals per hectare, with a hectare biomass of 20.193 kg. Due to the low biomass, the bad fish ecological status is also present in the Gesäuse National Park. The restructuring of the Johnsbach estuary in the course of the LIFE project can be seen as a successful upgrade measure. The lower course of the Johnsbach is a suitable growing habitat for juveniles and is therefore responsible for the positive development of the grayling stock in the examination area in the Gesäuse. In order to permanently improve the fish ecological conditions in the study area, a comprehensive remediation of the Enns is necessary, whereby the restoration of a natural water morphology as far as possible and the reduction of anthropogenic influence are seen as the most important steps.