Seasonal migration and habitat use of adult barbel (Barbus barbus) and nase (Chondrostoma nasus) along a river stretch of the Austrian Danube River

Abstract Migration patterns and habitat use of adult barbel ( Barbus barbus ) nase Chondrostoma nasus were monitored by radio telemetry over a period 13 months along 58-km-long section the Austrian part Danube River. The study site is confined upstream downstream two hydropower plants, contains larger tributary, Pielach Telemetry transmitters implanted into fish caught in this tributary after spawning June (25 individuals per species). results show that both species entire available width depth spectrum full migratable river length. Nase had an average home range 22.4 km, while was 34.4 km. differs significantly. While primarily encountered free-flowing section, mainly used deep areas impoundment during year. showed distinct fidelity to certain reach which periodically revisited. During season, homing behavior observed species. All seven could still be detected season returned (homing rate 100%). Six migrated up first migration barrier but did not pass existing passage facility. In contrast, only nine spawn 50%), most likely using location head section. Homing entered darkness.