Comparative fish stock surveys at Johnsbach and Enns as part of the EU LIFE project

The EU LIFE project Nature Conservation Strategies for Forest and Wild River in the Gesäuse (2005-2009) took place at Johnsbach and Enns. In this thesis, the fish stocks collected by electrofishing before and after the implementation of these steps were compared in order to examine the measures regarding their suitability for fish ecology. In spite of the measures taken, the catch figures on the Johnsbach were declining, which remained the same at the Enns. The assessment based on the Fish-Index-Austria showed that at Johnsbach an adaptation of the mission statement in the lower sections can only be achieved in a good ecological state, in the top section the assessment is insufficient due to the low biomass. Also on the Enns section Gesäuse was calculated an insufficient state of class 5 due to too low biomass values, in the Upper Gesäuse section only class 4 is reached, as in addition to the biomass the species spectrum ensures an unsatisfactory condition. In addition, a mapping of transverse structures was carried out at Johnsbach in order to evaluate them regarding their fitability for fish. This was done on the basis of a comparison of the altitude and flow velocity values with values of the swimming and jumping performance of the fish species from the literature. This showed that in all sections of the Johnsbach, where thresholds exist, there are currently impassable obstacles, at least for flops and juvenile salmonids. Since both Enns and Johnsbach were very short periods between the end of construction work and the exploitation of post-monitoring, a longer observation period is recommended in order to monitor the development of the measures taken and, if necessary, to take further necessary steps.