Effects of Wild Juvenile Spring Chinook Salmon on Growth and Abundance of Wild Rainbow Trout

Abstract

Abstract We investigated some of the ecological impacts to rainbow trout Oncorhynchus mykiss that could occur by supplementing spring chinook salmon O. tshawytscha in the upper Yakima River basin, Washington. Controlled field experiments conducted in three different streams indicated that presence of wild juvenile spring chinook salmon did not adversely affect growth of wild rainbow trout in high-elevation tributaries. Experiments at two spatial scales, habitat subunit and stream reach scales, were used to detect impacts. In small-enclosure experiments conducted in two tributaries to the Yakima River in 1993 and 1994, specific growth rates (SGRs) of wild rainbow trout paired with wild juvenile spring chinook salmon were not significantly lower than SGRs of their unpaired counterparts (1993: P = 0.360; 1994: P = 0.190). Stream reach experiments in another Yakima River tributary in 1995 also indicated that introductions of wild juvenile spring chinook salmon into 100-m-long enclosures, at a numerical densit...