Microhabitat selection by native brook trout and introduced rainbow trout in a small Pennsylvania stream

Due to species introductions, brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) occur together in many North American streams. Some have suggested that the two species do not compete because they select different habitats or are adapted to different environmental conditions. We assessed whether native brook trout and introduced rainbow trout selected different microhabitats in a small Pennsylvania stream. Underwater observations of brook and rainbow trout showed adult fish (greater than or equal to 90 mm total length) of both species were found significantly more often in deep water microhabitats than would be expected based on habitat availability. Total depth was the most important microhabitat variable in discriminating between the two species, irrespective of fish size. Adult rainbow trout were found in significantly deeper water than adult brook trout. Adult brook trout also were found significantly farther from cover and closer to the stream bottom than adult rainbow trout. Age-0 brook trout were found in significantly deeper water than age-0 rainbow trout. In small streams during low flow, water depth and distance to nearest cover are likely to be major factors in discriminating between brook and rainbow trout.