Fish migration and connecticity in the Danube River system

Research project P 14516 Fish migration and connectivity in the Danube River system Stefan SCHMUTZ 26.6.2000 The project focuses on fish migrations, especially on the different incidences and causes of migrations between the Danube River and an artificial side-arm-system, the Marchfeldkanal-System (NIFK-System). The aim is to provide more detailed knowledge on the migratory behaviour of selected species and the consequences of altered continuum conditions (longitudinal/lateral) in the Austrian Danube system. Due to their complex requirements fishes are sensitive indicators not only for habitat quality but also for the spatialemporal connectivity conditions within river systems. Although the significance of migration/movement within the life history of riverine fish has long been recognised, detailed information for most of the Danube fish species remains limited. We intend to study the interchange between a side-arm (WK-System) and the main river (Danube), on both the lower (outlet) and upper end (inlet) of the side-arm. Furthermore, we attempt to derive general migration patterns and strategies of the occurring species (60 Danube species). By intensive monitoring within a full two-year cycle, combined with existing knowledge, the goal is to obtain a fundamental basis for a classification of different fish species according to "migratory guilds". Working at a comparatively large scale will require a multi-method sampling approach. Fish migration will be investigated by means of 4 different major sampling strategies: - Permanent monitoring of fish migration (immigration/emigration) at three permanent monitoring stations. - Radio telemetry tracking of selected species/individuals will be performed within the NWK-System and the Danube itself - Drift sampling by means of an automatic drift sampler and drift nets at the upper- and lower end of the MFK- System. - Electro fishing within the MFK-System - faunal composition, population size and fluctuations will be recorded.

The project focused on investigations concerning fish migrations/movements in the Austrian part of the Danube- system. Migrations between Danube and an artificial sidearm (Marchfeldkanal-system), respectively a tributary (River Pielach) were monitored. Within the course of the project migrations of juvenile stages as well as adults were investigated by means of different methods. Most outstanding results were gained by studying migrations of nase, barbel and Danube-roach using radio telemetry. Nase and barbel were tagged after spawning in River Pielach, a tributary of the Danube in a section called Wachau. A total of 50 specimens were tagged and their migrations subsequently monitored over a one year period. It could be shown, that nase almost exclusively used free flowing Danube sections, whereas barbels mainly inhabited the impounded sections throughout the year. The entire river bed was used by both species. Up to now it was assumed, that both species mainly inhabit riparian areas. Both species showed migration distances of more than 50 km. During the following spawning period the major part of tagged fishes migrated back into the tributary, which clearly demonstrates the general importance of tributaries as reproduction areas for Danube fish populations. This study produced evidence that also Danube species show distinct homing behaviour. This was so far well known for salmons but unexplored for nase and barbel. The radio telemetry experiment at the Machfeldkanal was done with Danube roaches (18 fishes). As a main result it can be concluded, that this endangered species uses flowing sections of the river, exclusively. Impounded sections were avoided. The fishes did not migrate more than 5 km. Male specimens moved more frequently than females. One main focus at the Marchfelkanal was to grasp exchanges of fish between Danube and the side-arm. Throughout the year almost no migrations between main river and branch were observed. The only exceptions occurred in case of flood events in the Danube, during that increasing numbers of immigrants could be observed. Inside the Marchfelkanal-system it could be shown, that during winter mainly juvenile stages move out of the sidearm into the Danube, which underlines the overall importance of side waters as spawning and nursery habitat. By doing this research project we were able to generate new insights into the ecology and requirements of Danube fish species. All members of EU are bound by the Water Framework Directive to improve the status of river- ecosystems. To gain fundamental ecological knowledge is a basic requirement for being able to develop efficient protection and restoration programmes in the future.