Effect of fluctuating flow and temperature on cover type selection and behaviour by juvenile brown trout in artificial flumes

Brown trout Salmo trutta in a flume used cover more often and were more agg regated at low water temperatures in winter compared with summer. Cover com binations providing the most cover (overhead, visual and velocity cover) we re preferred in winter whereas velocity refuges were preferred in late summ er; and brown trout rarely used any of these cover structures in early summ er. Flow affected cover use especially in winter, when most of the trout mo ved to shelters during the first high flow period. Movements by brown trout were most frequent in early summer. The much higher aggression rate in sum mer compared with winter decreased during the first period of high flow in both summer experiments. The results indicate seasonal changes in cover hab itat and cover type preferences suggesting that habitat complexity is impor tant, and availability of cover is particularly important during different seasons and fluctuating flow. (C) 2000 The Fisheries Society of the British Isles.