Habitat use by chub (Leuciscus cephalus L. 1766) in a large river, the French Upper Rhone, as determined by radiotelemetry

Two tracking experiments on adult chub were conducted in the French Upper R hone River to study the use of both habitat and cover, the daily and season al variation in activity and movement, and to relate these to environmental factors. In summer 1997 and in winter 1998, ten fish were internally tagge d with motion-sensitive transmitters. A significant occupation of backwater s and cover structures such as woody debris and clusters of boulders by chu b was evidenced on both a daily and a seasonal basis. No stable diel patter n in mobility rates and activity levels was observed and fish showed smalle r home range, lower mobility rates, and lower activity levels in winter. Wi thin both seasons, activity and movement did not show significant correlati on with water temperature or river discharge. However, three fish sheltered in backwaters and two others disappeared during peak flow associated with the release of water from a hydroelectric dam. This sheltering behaviour du ring flood events stresses the importance of still waters connected with th e active channel, and habitat diversity.