Competition Between Non-Native Brook Trout and Coho Salmon in the Elwha River, WA during Dam Removal

In dammed rivers with multiple anthropogenic influences, barrier removal alone does not necessarily ensure recovery. Other human impacts, such as the introduction of non-native species, need to be considered during the restoration process. The removal of two fish-passage-prohibiting dams on the Elwha River (WA, USA) provides an unprecedented opportunity to study novel native-nonnative salmonid interactions. During recolonization, anadromous salmonids will encounter established non-native brook trout (Salvelinus fontinalis) populations stocked after dam construction. Brook trout and juvenile coho salmon (Oncorhynchus kisutch) have several life history commonalities, including emergence time and habitat preference. These ecological overlaps suggest that the two species might compete for food and space in environments where these resources are limiting, and competition could limit the success of coho salmon recolonization. Here we present an examination of food and habitat resource use to reveal the potential extent and spatial scale of competition between the species. We also present results from competition feeding trials in laboratory streams that suggest juvenile coho salmon are competitively dominant to brook trout, regardless of size difference between individuals and even when outnumbered by competitors. This work has important implications for scientists and managers working to ensure successful salmonid recolonization of the Elwha River.