Distribution of three euryoecious cyprinids in the main channel of the Lower River Rhone
Carrel, G.; Rivier, B.
Two centuries of anthropogenic influences have induced severe alterations in the Rhône River ichthyocoenosis. Changes in diversity and relative species dominance have been noted. The Lower Rhône is marked by a succession of hydropower schemes. The main channel serves alternately as raceways and reservoirs. In certain places it also supplies water to nuclear plants and collects cooling water. Contemporary fish communities in the highly regulated channel are greatly unbalanced and are dominated by three euryoecious Cyprinidae: bleak Alburnus alburnus, roach Rutilus rutilus and chub Leuciscus cephalus. Species distribution is principally determined by location and structural characteristics of habitat in the embanked stream margins. Fluctuations in abundance that have been observed between 1987 and 1994 are mainly determined by temperature and significant hydrological events: low discharge from 1989 to 1993 and high floods from October 1993 to January 1994.