Great Basin Naturalist


Abundance of rainbow trout (Oncorhynchus mykiss) in relation to characteristics of pockets created by boulders was studied in Fall River, southeastern 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 habitat selection in the following terms: the most suitable habitat was ≥0.7 m maximum depth, ≥0.5 m minimum depth, and ≥3 in2 surface area. Some study reaches of Fall River had more suitable pockets available for trout than were being utilized.