Habitat Utilization and Behavioral Interaction of Juvenile Atlantic Salmon (Salmo salar) and Rainbow Trout (S. gairdneri) in Tributaries of the White River of Vermont

Competition for space between stocked juvenile Atlantic salmon, Salmo salar, and wild juvenile rainbow trout, S. gairdneri, was examined in stream channel experiments, a field experiment, and in field habitat surveys. In stream channels providing riffle and pool habitats, species differed in their distribution both as underyearlings (0+) and as yearlings (1+). Yearling salmon occurred more often in stream channel riffles during trials with 1+ rainbow trout than during trials testing only salmon; trout distributions in the channels were unaffected by salmon. In a field experiment conducted to determine if the stocking of 0+ Atlantic salmon causes the displacement of resident 0+ rainbow trout, salmon fry were stocked at a density of 85 per 100 m2. Emigration from the stocked zone and an unstocked control zone were then monitored daily with four weirs. The 0+ salmon had no apparent effect on the rate of movement of resident rainbow trout fry. During summer and fall field surveys, 0+ salmon occupied deeper and swifter water than 0+ rainbow trout; as yearlings these species occupied similar habitats. In late fall, segregation by habitat occurred: Atlantic salmon were primarily in riffles; rainbow trout were primarily in pools. We found no evidence of competition between cohorts of underyearlings; however, the niche shift by 1+ salmon in the stream channels suggested that, at times, juveniles of these species will compete for space.