THE EFFECTS OF RECREATED INSTREAM AND ECOTONE STRUCTURES ON THE FISH FAUNA OF AN EPIPOTAMAL RIVER

Investigations of fifteen sections of seven Austrian epipotamal (barbel region) streams between 1981 and 1984 demonstrate the impact of instream river bed structures on fish communities. Reduced spatial heterogeneity due to river straightening resulted in decreasing species number, diversity, stock density and biomass. Reincreased variability of the river bed in the frame of a subsequent restructuring project improved all community-specific values significantly within a 3-year investigation period (1988-1990). Besides the regained habitat variability in form of riffle pool sequences and other instream structures, the newly created riparian zones obviously provided important niches, e.g, as refuge areas during flooding and as nursery grounds for fish fry. The positive effects of the recreated land/water ecotone are discussed with respect to river restoration projects.