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Date Permissions Signed
Date of Award
Department or Program Affiliation
Huxley College of the Environment
Master of Science (MS)
Helfield, James M.
Miner, Benjamin G., 1972-
O'Neal, Jennifer S.
Bodensteiner, Leo R., 1957-
The decline of Pacific salmon (Oncorhynchus spp.) is well-documented, and freshwater habitat degradation is a primary contributor. Despite decades of river restoration, salmon populations have not significantly recovered. Large woody debris (LWD) placement is one of the most common forms of restoration. To evaluate the effectiveness of this restoration method, I analyzed long-term monitoring data from 16 LWD placement projects throughout Washington State, implemented between 2004 and 2015. Each project followed a multiple Before-After, Control-Impact study design, which monitored physical habitat and fish populations. I used a series of linear mixed models to evaluate both habitat and fish response. I found that habitat features responded positively, with increases in average residual pool depth, pool area, and habitat complexity. However, fish response varied by species and location. I looked for changes in both abundance and size of juvenile coho (O. kisutch), Chinook (O. tshawytscha) and steelhead/rainbow trout (O. mykiss). The average size of O. mykiss increased over time. Coho and coastal Chinook populations were largely unaffected, indicating that these populations are limited by factors unaddressed by LWD placement. Inland Chinook populations increased in abundance immediately, but declined in average size over time, indicating over-crowding at restoration sites due to a lack of high-quality habitat. My results demonstrate that LWD placement is effective at improving freshwater salmon habitat, but these improvements are not generating consistent increases in juvenile salmon abundance or biomass, suggesting that LWD placement does not always address the limiting factors for salmon production. Broader threats to salmon recovery, including declining ocean conditions, climate change, and dams, must also be addressed to improve effectiveness of restoration. My findings also highlight the vital need for comprehensive, long-term monitoring of restoration actions to guide future salmon recovery efforts.
salmon, restoration, Oncorhynchus, restoration effectiveness, large woody debris, linear mixed models, habitat, long-term monitoring
Western Washington University
Subject – LCSH
Coarse woody debris--Washington (State); Stream restoration--Washington (State); Restoration ecology--Washington (State); Pacific salmon--Effect of habitat modification on--Washington (State); Fish populations--Washington (State)
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Walls, Caroline J., "The Effectiveness of Large Woody Debris Placement at Improving Freshwater Rearing Habitat and Enhancing Juvenile Salmon (Oncorhynchus spp.) Production" (2020). WWU Graduate School Collection. 937.