Temporal environmental variation and spatial patterns in densities of young-of-the-year rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta)

Densities of rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) young-of-the-year were monitored at six sites in three reaches of a mountain river for I I years. Relative differences in mean density of young-of-the-year among reaches were consistent Over time (no year x reach interaction) for rainbow trout, but not for brown trout. Some reaches consistently held more young-of-the-year brown trout and rainbow trout than other reaches, and in any one year the rankings of reaches based on the density of each species varied similarly. The findings suggest that year-to-year environmental variation complemented and sometimes modified the apparent contribution of reach properties for structuring spatial patterns in young-of-the-year density.