Linkages Between Grazing Indicators, Habitat Diversity, and Fish Diversity and Assemblage Structure

Grazing reduces riparian vegetation and results in trampled and unstable stream banks, which in turn leads to channel widening and sedimentation.  Wide, shallow, sediment-laden stream channels lack instream habitat diversity important to stream fishes.  Our goal was to evaluate the effect of grazing on instream habitat diversity and fish diversity in Goose Creek, a Snake River tributary (Idaho-Nevada-Utah boarder).  Data from 37 sites sampled in 2013 and 2014 showed fish species diversity to be positively associated (P<0.15) with four dimensions of habitat diversity as revealed by a multiple linear regression that explained 62% of the variance in fish species diversity (adj-R²=0.62).  Variation in each of the four dimensions of habitat diversity was explained, to varying degrees, by grazing indicators after accounting for persistent stream-size effects whereby habitat diversity was higher in larger streams.  A canonical correspondence analysis (CCA) revealed fish assemblage structure to be significantly associated with temperature (P<0.01), percent slope (P=0.02), SD of velocity (P=0.01), percent woody vegetation (P<0.01), percent stream bank sloughing and slumping (P=0.10), and percent fine substrates (clay/silt/sand; P=0.11).  Our results provide insight into how grazing management influences instream habitat diversity and other habitat features that structure fish species diversity and assemblage structure.