Relationship of winter concealment habitat quality on pool use by juvenile spring Chinook salmon (Oncorhynchus tshawytscha) in the Grande Ronde River Basin, Oregon USA

Abstract

Winter concealment habitat quality was assessed and its use by juvenile spring Chinook salmon (Oncorhynchus tshawytscha) quantified in three hatch- ing areas of the Grande Ronde River Basin, Oregon USA. Fish densities were significantly higher in pools with a higher winter concealment habitat index than pools with a lower index. The mean fork length and mean growth rate of fish did not differ between pools with a higher or lower winter concealment habitat index, even though residual fish were significantly larger than fish that emigrated. Biomass-density was significantly higher in pools with a higher winter concealment habitat index than pools with a lower index in all three hatching areas. Biomass-density was positively associated with the amount of cobble substrate (10-24.9 cm/m 2 ) in all three hatching areas, and inversely associated with embeddedness in two of the hatching areas. Results of this study indicate that enhancing winter concealment habitat could improve habitat quality resulting in increased carrying capacity and winter usage by juvenile spring Chinook salmon.