Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4348
Title: Combined effects of climate change and bank stabilization on shallow water habitats of Chinook salmon
Author: J. C. Jorgensen, Michelle M. McClure, M. B. Sheer, N. L. Munn
Other Contributor: Nancy L. Munn
Publication Year: 2013
Journal: Conservation Biology
Volume: 27
Issue: 6
Pages: 1201-1211
Keywords: Endangered Species Act (ESA),climate change,section 7 consultation,habitat,Chinook salmon,Willamette River

 Significant challenges remain in the ability to estimate habitat change under the combined effects of natural variability, climate change, and human activity. We examined anticipated impacts on shallow water over low-sloped beaches to these combined effects in the lower Willamette River, Oregon, an area highly altered by development. A proposal to stabilize some shoreline with large rocks (riprap) would alter shallow water areas, an important habitat for threatened Chinook salmon (Oncorhynchus tshawytscha), and would be subject to U.S. Endangered Species Act-mandated oversight. In the main stem, subyearling Chinook salmon appear to preferentially occupy these areas, which fluctuate with river stages. We estimated effects  with a geospatial model and projections of future river flows. Recent (1999-2009) median river stages during peak subyearling occupancy (April-June) maximized beach shallow water area in the lower main stem. Upstream shallow water area  was maximized at lower river stages than have occurred recently. Higher river stages in April-June, resulting from increased flows predicted for the 2080s, decreased beach shallow water area 17- 32%. On the basis of projected 2080s flows, more than 15% of  beach shallow water area was displaced by the riprap. Beach shallow water area lost to riprap represented up to 1.6% of the total from the mouth to 12.9 km upstream. Reductions in shallow water area could restrict salmon feeding, resting, and refuge from predators and potentially reduce opportunities for the expression of the full range of life-history strategies. Although climate change analyses provided useful information, detailed analyses are prohibitive at the project scale for the multitude of small projects reviewed annually. The benefits of our approach to resource managers include a wider geographic context for reviewing similar small projects in concert with climate change, an approach to analyze cumulative effects of similar actions, and estimation of the actions’ long-term effects.

Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Describe the relationship among human activities and species stock status, recovery, rebuilding and sustainability.
Investigate ecological and socio-economic effects of alternative management strategies or governance structures.