Assessment of Columbia River Salmonid Populations Using a Landscape Approach: An Application for the National Fish Habitat Partnership

The 2010 NFHP national assessment of river habitats yielded data and approaches that serve as a beginning point for subsequent finer-scale regional studies.  While habitat condition scores were based on threshold responses of sensitive stream fishes to human disturbances, this project focuses on characterizing relationships of salmonid populations to landscape scale disturbances including urbanization and agriculture.  Our approach compares NFHP condition scores for streams containing viable salmon populations within the Columbia River Basin to those of streams not containing salmon populations.  Species of interest include Chinook salmon, steelhead, and Coho salmon, as well as distinct sub-populations of each species.  We first attributed all salmonid data to NHDPlusV1 stream reaches, mapped taxa distributions, and identified the strongest taxa-landscape disturbance relationships within the basin.  Next, we characterized differences in expected relationships between salmonids and habitat condition by evaluating region-wide water quality, measures of river fragmentation, and protected lands – data that were previously unavailable.  Finally, we attempted to identify threshold responses of Chinook salmon to abundances of various fish species with which negative interactions are common (e.g., pikeminnow).   This information yields new insights that will inform the 2015 national assessment of river habitats and provides additional knowledge related to landscape influences on salmonids.