Use of Thermal Refugial Areas on the Klamath River by Juvenile Salmonids; Summer 1998

Abstract During the summer of 1998, the Yurok Tribal Fisheries Program observed and documented,salmonid use of thermal refugial areas located near the mouths,of cool-water tributaries in the Klamath River from Iron Gate Dam to Bluff Creek. Juvenile Chinook salmon and juvenile steelhead were observedmaking,extensive use of these areas during the summer months. No coho were observed using these areas, despite searching, and crew training. 24 hour observations revealed that juvenile fish leave refugial areas and make extensive use of nearby mainstem areas, presumably to take advantage of the greater food resources located in the mainstem Klamath. Physical measurements revealed a great diversity in size of refugial areas; from 4 m,, and refugial areas showed,a great deal of variability with regard to habitat complexity. When,flow releases at Iron Gate Dam were increased from 1140 to 1390 cfs, the refugial area located at the mouth of Indian Creek was reduced in aerial extent and volume, but still appeared