Hydropeaking effects on movement patterns of brown trout (Salmo trutta L.)

Radiotelemetry was used to investigate seasonal movement and home range of brown trout Salmo trutta (size range 188-420 mm fork length, N = 30) in two reaches of the Noguera Pallaresa River (Ebro Basin, north-east Spain) subjected to different flow regulation schemes. NP-1 reach is a bypassed section with near natural flow conditions, whereas the downstream reach NP-2 is subjected to daily pulsed flow discharge (i.e., hydropeaking) from an upstream hydropower station. Significant differences in home range size (95% kernel estimates) and seasonal movement pattern between study reaches were found. Mean home range size was (mu +/- SE) 112.1 +/- 11.5 m in the bypassed reach NP-1 and increased significantly in the hydropeaking reach NP-2 up to 237.9 +/- 37.2 m. There was a large individual variability in fish home range size within reaches. Most of the seasonal differences in fish movement among reaches were associated with the spawning season. Pulsed discharge events in NP-2 during daytime in summer (lasting about 3 hr and increasing water flow from 1 to 20 m(3)/s) did not cause significant displacements in either upstream or downstream direction during the duration of the event. Our results highlight the importance of habitat connectivity in hydropeaking streams due to the need of brown trout to move large distances among complementary habitats, necessary to complete their life cycle, compared with unregulated or more stable streams.