USE OF BOULDER POCKET HABITAT BY RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) IN FALL RIVER, IDAHO

Abundance of rainbow trout (Oncorhynchus mykiss) in relation to charac teristics of pockets created by boulders was studied in Fall River, so utheastern Idaho. To determine depth and surface area of pockets most selected by rainbow trout, fish were counted by snorkeling, and pocket physical dimensions were measured. An electivity index defined habita t selection in the following terms: the most suitable habitat was grea ter than or equal to 0.7 m maximum depth, greater than or equal to 0.5 m minimum depth, and greater than or equal to 3 m(2) surface area. So me study reaches of Fall River had more suitable pockets available for trout than were being utilized.