Flexible Summer Habitat Selection by Wild, Allopatric Brown Trout in Lotic Environments

Spatial and temporal hydraulic heterogeneity influence distributional patterns of species in streams. Ecological theory suggests flexible habitat selection strategies are favored in such unstable environments. The effects of varying hydraulic conditions on habitat selection by brown trout Salmo trutta in summer were studied in eight streams in Norway and Scotland. At normal summer flows, brown trout averaging 16 cm total length (SD = ±5 cm, range = 3-43 cm) were selective in habitat use. The selection window was relatively narrow for focal water velocity (mean = 14 cm/s, median = 10 cm/s, 60.1% of observations ≤14 cm/s). Trout favored slower flowing pool areas, but selection ranges were wide (mean water column velocity = 24 ± 21 cm/s, range = 0-142 cm/s; mean depth = 69 ± 29 cm, range = 9-305 cm). Larger fish used deeper habitats; other variables did not correlate with size. Great overlaps in spatial niche used by the studied size-classes of trout indicated versatility in habitat selection (e.g.,...