The importance of inshore areas for spawning nase Chondrostoma nasus (Cyprinidae) in a free-flowing section of a large river (Danube, Austria)
Keckeis, H.; Frankiewicz, P.; Schiemer, F.
An analysis of several morphological variables derived from riverbank profiles was undertaken to characterize potential spawning sites for Chondrostoma nasus in a free-flowing section of the Austrian Danube at Vienna (from river-km 1945 to 1896). Fish distribution in 1992 and 1993 was evaluated by electrofishing during the reproductive period. A cluster analysis revealed three significantly different inshore types, characterized by distance and its variability from the waterline to depths of 1, 2 and 3 m, and by lengths of isobathic lines at these depths within a 1 km stretch of river. Relationships between the inshore variables and different inshore types were analysed by principal component analysis. Fish densities (in terms of catch-per unit-effort) during the reproductive period were highest on uniformly-structured gravel-banks with relatively steep slopes. The distribution of the three distinct inshore types indicated the important role of the northern part of the investigated river stretch (upstream from river-km 1915) as a reproductive zone for C. nasus.