Document Type

Thesis

Date of Degree Completion

Spring 2021

Degree Name

Master of Science (MS)

Department

Biology

Committee Chair

Clay Arango

Second Committee Member

Paul James

Third Committee Member

Alexa Maine

Abstract

Historically, oligotrophic Pacific Northwest (PNW) streams received annual returns of spawning anadromous fish that provided resource subsidies in the form of marine-derived nutrients (MDN), thus driving stream food web productivity. To date, many studies in the PNW have focused on Pacific salmon (Oncorhynchus spp.) as a resource subsidy, overlooking other anadromous fish species such as Pacific lamprey (Entosphenus tridentatus). Both Pacific salmon and Pacific lamprey are culturally important to PNW tribes for ceremonial, medicinal, and subsistence purposes, and have been since time immemorial. Unfortunately, both salmon and lamprey populations are in decline. Historically, lamprey have been disregarded and actively eradicated by non-tribal resource managers, and although they have recently been included in restoration considerations, their role as a resource subsidy is still poorly understood. In order to better understand how Pacific lamprey can subsidize stream food webs, I used a nutrient diffusing substrate (NDS) array amended with Pacific lamprey and tule fall Chinook salmon tissue to compare the basal food web response in the summer and fall, when lamprey and salmon spawn, respectively. This study was conducted in the upper Yakima River basin where the Yakama Nation has an active adult lamprey translocation program. I measured chlorophyll a as the autotrophic food web response and community respiration (CR) as the heterotrophic food web response. Chlorophyll a responded equally to lamprey and salmon but was significantly higher in the summer. Alternatively, CR had a higher response to salmon compared to lamprey and was significantly higher in the fall. Differences observed in food web response were dictated by season, where chlorophyll a nutrient response ratios (NRRs) were roughly twice as high as in the summer and CR NRRs were roughly twice as high as in the fall. Stoichiometric differences in lamprey and salmon tissue likely facilitated this response and had C:N:P ratios of roughly 187:37:1 and 60:13:1 respectively. These results indicate that Pacific lamprey are equivalent to salmon as a resource subsidy for the autotrophic food web in the summer when lamprey would normally spawn and suggest that increased lamprey populations will drive stream food webs that support both lamprey and salmon.

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