ENDANGERED FISH SPECIES OF THE DANUBE RIVER IN AUSTRIA

The ecological affinity of fish species to different habitat types in the course of their life cycles is investigated in the free-flowing sections of the Austrian Danube. The results point to the great significance of the degree of hydrological integration between the river and its adjoining waters. In the breeding and fry stage, rheophilic species are bound to the river itself, but the preferred zones show great variations according to both fish age and species. A highly structured shoreline is important in providing a gradient of water current and a spectrum of food sources. Regulated embankments are characterized by an extremely reduced fauna with low population densities of eurytopic species. These results give evidence that the conservation of the characteristic species association is incompatible with the planned hydroelectric power dams in the remaining, free flowing zones of the Danube. The importance of the fish fauna as an indicator group for the condition of large river systems is discussed from the conservation point of view.