Geomorphic and Riparian Influences on the Distribution and Abundance of Salmonids in a Cascade Mountain Stream

2 Graduate Research Assistant and Associate Professor of Fisheries, respectively, Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR, 97331, USA. Abstract: Abundance of resident cutthroat (Salmo clarki) and rainbow (Salmo gairdneri) trout was generally 1.5 to 3.5 times greater in unconstrained reaches than in constrained reaches of Lookout Creek, a fourth-order tributary to the McKenzie River, Oregon. The presence of adult rainbow trout depressed juvenile abundance in pools with little habitat complexity but had no effect in pools with more heterogeneous structure. The greater abundance of trout in unconstrained reaches was related to habitat structure, the influence of the riparian canopy on stream productivity, and the effect of channel morphology on stream hydraulics. Valley floor landforms are major determinants of channel complexity and habitat structure, providing a hierarchical geomorphic context for interpreting riparian influences on patterns of abundance and distribution of salmonids within a basin.