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Date of Award



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Document Type

Thesis: EWU Only

Degree Name

Master of Science (MS) in Biology



First Advisor

Dr. Camille McNeely

Second Advisor

Dr. Allan Scholz

Third Advisor

Prof. Matthew Hodgson


This research was conducted to determine the effects of salmon mediated marine-derived nutrient subsidies on benthic macroinvertebrate production. The Cascade Columbia Fisheries Enhancement Group (CCFEG) is evaluating whether stream nutrient enhancement might benefit struggling salmon populations in the Wenatchee River Watershed. To evaluate the potential benefit of enhancement, the Wenatchee Nutrient Assessment was conducted on Nason Creek, and the Chiwawa, White, Little Wenatchee and upper Wenatchee rivers. Historically these tributaries to the upper Wenatchee River experienced prolific runs of anadromous salmon, which provided a major nutrient subsidy during spawning events. As a result of decreased salmon populations, these rivers are deprived of that nutrient pulse. It has been suggested that, due to the reduced nutrient subsidy, the streams are not producing the food base necessary to support healthy numbers of rearing anadromous fish. Nutrient assessment is the first phase of a potential nutrient enhancement project, where the streams would be fertilized with salmon carcasses or carcass analogues to bolster lower trophic levels and promote juvenile salmonid production.

In this study, I estimated benthic macroinvertebrate secondary production at two locations within the White River, a lower site within a distinct sockeye salmon spawning reach, and an upper site upstream of the spawning reach. Through regular sampling I determined the biomass produced by the macroinvertebrate assemblage and 10 individual taxa during one year. Assemblage annual production was higher at the upper site than at the lower site, 75,233 mg DM∙m-2∙y-1 vs.43,202 mg DM∙m-2∙y-1, respectively. Although there appears to be a large disparity between the two sites, 95% confidence intervals generated using error propagation revealed no significant difference between sites.

I also compared results from the White River to biomass and densities of macroinvertebrates sampled from Nason Creek and the Chiwawa, Little Wenatchee, and Wenatchee Rivers. These rivers were sampled three times, fall 2012, spring 2013, and fall 2013. Patterns for biomass and density were not consistent in and among rivers. In the White River, there was significantly higher biomass and abundance of invertebrates in the upstream reach compared to the spawning reach; there were no significant differences within the other rivers.

The lower White River is the model salmon-bearing stream to which the other rivers were compared. The differences in biomass, density, and community composition between the upper and lower White River reaches suggest that spawning salmon alter macroinvertebrate communities through marine-derived nutrient subsidies and bioturbation. Further, the low densities and biomass of multivoltine taxa in the lower White River indicates that despite its substantial run of returning sockeye salmon, the river may still have a limited food base for rearing salmonids. However, the causes of this limitation are unclear, and studies of the interaction between bioturbation and MDN are recommended.