In the John Day basin of Oregon, Li et al. examined the cumulative effects of riparian disturbance by grazing on the trophic structure of high desert trout streams. Watersheds with greater riparian canopy had higher standing crops of rainbow trout (Oncorhynchus mykiss), lower daily maximum temperatures, and perennial flow. Trout abundances were negatively correlated with solar input in both watershed clusters. Over all age classes, trout densities in watersheds of cluster N (northerly draining streams) were negatively correlated with temperature and solar input and positively associated with substrates free of silt. Densities of trout of all age classes in watersheds of cluster S (southerly draining streams) were negatively correlated with solar input, but positively associated with discharge and depth. Positive correlations of these indices indicate that higher densities were found where riparian and bank conditions were of higher quality. Significant positive correlations were found between solar input and algal biomass, algal biomass and total invertebrate biomass, and total invertebrate biomass and herbivorous invertebrate biomass. There was no significant correlation between trout biomass and either total invertebrate biomass or herbivorous biomass. Stream temperature elevations can be lethal and may impose high metabolic costs on rainbow trout, which may offset higher food availability and affect the availability of the prey.
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