Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 5992
Title: Landscape models to understand steelhead (Oncorhynchus mykiss) distribution and help prioritize barrier removals in the Willamette Basin, Oregon, USA
Author: E. Ashley Steel, Blake E. Feist, D. Jenson, G. R. Pess, M. B. Sheer, J. Brauner, R. E. Bilby
Publication Year: 2004
Journal: Canadian Journal of Fisheries and Aquatic Sciences
Volume: 61
Issue: 6
Pages: 999-1011

We use linear mixed models to predict winter steelhead (Oncorhynchus mykiss) redd density from geology, land use, and climate variables in the Willamette River Basin, Oregon.  Landscape variables included in the set of best models were alluvium, hillslope < 6%, landslide-derived geology, young forest (< 40 years), shrub vegetation, agricultural land use, and mafic volcanic geology.  Our approach enabled us to model temporal correlation between annual redd counts at the same site while extracting patterns of relative redd density across sites that are consistent even among years with varying strengths of steelhead returns.  We used our model to predict redd density (redds/km) upstream from 111 probable migration barriers, as well as 95% confidence intervals around redd density predictions and total number of potential redds behind each barrier.  Using a metric that incorporates uncertainty, we identified high-priority barriers that might have been overlooked using only stream length or mean predicted fish benefit, and we clearly differentiated between otherwise similar barriers.  We show that landscape features can be used to describe and predict the distribution of winter steelhead redds and that these models can be used immediately to improve decision-making for anadromous salmonids.

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