Characteristics of Deep Pools Used by Adult Summer Steelhead in Steamboat Creek, Oregon

This study examined environmental factors that affect deep‐pool use by adult summer steelhead Oncorhynchus mykiss in Steamboat Creek, Umpqua River basin, Oregon. Deep pools (>0.8 m depth) represented only 4% of the available habitat area, and 39% of these pools had a mean bottom temperature not exceeding 19°C. Fish and habitat surveys were conducted in August and the first half of September of 1991 and 1992. The presence of adult summer steelhead in pools was determined by snorkeling and visual inspection, and the physical, chemical, and geomorphic characteristics were measured. Differences in deep‐pool use by summer steelhead and their relationship to environmental characteristics were assessed by descriptive canonical discriminant analysis. The canonical function explained 69% of the variation in deep‐pool use and defined a gradient from long, shaded deep pools with a coarse substrate and colder bottoms (which fish used) to shorter, shallower, sunny pools with fine particulate substrate, homogeneous water temperatures, and warmer bottoms (which fish did not use). This indicates that pool occupancy by adult summer steelhead in Steamboat Creek is a result of the interaction of geomorphic characteristics, cover, and thermal conditions. Future research should be directed toward understanding how biotic interactions within pools, deep‐pool patchiness, and overall riverscape conditions influence summer steelhead distribution and pool use.