Johnsbach — Post-Monitoring Fish Ecology. Analysis of the effect of implemented flux building measures

As part of the LIFE project Nature Conservation Strategies for Forest and Wild River in the Gesäuse, LIFE05/NAT/A/78 (2005 2010), structural improvement measures were carried out on the Johnsbach alongside other hydrological and conservation activities. Due to the ecologically oriented dismantling of hard construction elements, such as crashes, soil sills and wire gravel beans, as well as by expanding the creek bed, the Johnsbach was redesigned near nature. The removal of transverse barriers from the creek bed is crucial for the longitudinal fish passability from the Enns upstream. The species Coppe (Cottus gobio), listed in Annex II to the Flora-Fauna Habitats Directive (RAT OF THE EUROPEAN COMMUNITIES 1992), has only a limited swimming capacity. Even small obstacles can affect their migrations, isolate populations from each other and even lead to a complete local disappearance of the species (BUNDESAMT FOR ENVIRONMENT, WALD AND LANDSCHAFT, 2004 according to TOMLINSON & Perrow, 2003) The Technical Office for Water Ecology was commissioned by the Wildbach- und Avalanchebauung (WLV), Construction Manager Steiermark Nord, to investigate the effect of implemented river construction measures by means of fish stock surveys in Johnsbach as part of the post-monitoring project. In 2005, the University of Soil Culture (BOKU), Institute of Hydrobiology and Water Management (IHG) carried out a pre-monitoring of fish stocks (WIESNER et al., 2006). After the removal and adaptation of numerous artificial transverse structures in the underpass of the Johnsbach, a first post-monitoring was carried out in 2009 (KAMMERHOFER, 2010), with four sections from pre-monitoring being fished again. In order to ensure the comparability of the results, these four sections were fished again in autumn, between 5.10.2015 and 7.10.2015. In addition, the fish stock was collected in two other sections of the Johnsbach, one of these two routes already from WIESNER et al. (2006) was sampled. These are two sections, characterised by strong construction, which have been examined in terms of continuity for the fish fauna. In principle, it should be noted that the restoration measures under the LIFE project have improved the fish stock in Johnsbach. No fish deposits were detected in the first sampled route above the sliding dosing barrier in the upper reaches of the Johnsbach. Due to the high crash, this transverse structure is impassable for fish. How far fish occur in the upper course of the Johnsbach is not documented.