Competition between non-native brook trout and coho salmon in the Elwha River, WA during dam removal

Abstract

The removal of two dams on the Elwha River, WA is the largest dam removal project in US history. A major goal of this project is to restore historically abundant populations of Pacific salmon to the river, so it is important to know if competition between resident and anadromous species could inhibit salmon recolonization. We investigated competitive interactions in laboratory streams to determine how species, size, and group size affected competitive dominance and determined the level of habitat and prey resource use overlap to indicate the potential for competition in reaches of the Elwha River. Coho salmon were competitively dominant over brook trout regardless of size difference or group size, and will likely outcompete brook trout in the wild if resources become limited. Prey resource use overlap indicated potential for competition in sympatric areas, but density and distribution patterns did not suggest that competition was occurring at the reach scale.