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

Abstract

Two tracking experiments on adult chub were conducted in the French Upper Rhone River to study the use of both habitat and cover, the daily and seasonal variation in activity and movement, and to relate these to environmental factors. In summer 1997 and in winter 1998, ten fish were internally tagged with motion-sensitive transmitters. A significant occupation of backwaters and cover structures such as woody debris and clusters of boulders by chub was evidenced on both a daily and a seasonal basis. No stable diel pattern in mobility rates and activity levels was observed and fish showed smaller home range, lower mobility rates, and lower activity levels in winter. Within both seasons, activity and movement did not show significant correlation 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 during flood events stresses the importance of still waters connected with the active channel, and habitat diversity.