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Date of Award

Summer 2025

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Science

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Helfield, James M.

Second Advisor

Bodensteiner, Leo R., 1957-

Third Advisor

Lofgren, Rebecca

Abstract

Cold, glacially influenced headwater streams are recognized as critical thermal refugia for cold-water fish species such as bull trout (Salvelinus confluentus), which are highly sensitive to warming temperatures and face significant threats from climate change and non-native species. The cold waters of glacial streams not only provide essential thermal conditions for bull trout but may also exclude non-native species like brook trout (Salvelinus fontinalis) that compete with or displace bull trout. My study assesses the distribution of bull and brook trout in two glacial headwater rivers within Mount Rainier National Park, an area that includes federally designated critical habitat for bull trout under the U.S. Endangered Species Act. Using environmental DNA (eDNA) sampling and spatial stream network modeling (SSNM), I examined the relationship between fish presence and water temperature to understand thermal occupancy within glacial headwaters. Results showed that bull trout were widely distributed across the study site and detected at temperatures as low as 3 °C. Brook trout were concentrated in the warmest areas of the study area, being most prevalent between 6 and 8 °C, with the probability of their presence increasing as temperatures increased. Brook trout were nonetheless observed at temperatures as low as 4.25°C, which indicates a lower thermal tolerance than previously documented and calls into question the idea that temperature is a limiting factor for their distribution. My findings present evidence that brook trout may be more tolerant of cold stream temperatures than previously thought, and low stream temperatures may not be as strong of a barrier to invasion. Greater understanding of thermal occupancy of bull trout and brook trout in glacial headwaters is necessary to inform management strategies to mitigate the risk of bull trout extirpation in these vulnerable ecosystems.

Type

Text

Keywords

bull trout, brook trout, glacially influenced streams, glaciers, climate change, temperature

Publisher

Western Washington University

OCLC Number

1530410184

Subject – LCSH

Bull trout--Effect of temperature on--Washington (State)--Mount Rainier National Park; Brook trout--Effect of temperature on--Washington (State)--Mount Rainier National Park; Bull trout--Habitat--Washington (State)--Mount Rainier National Park; Brook trout--Habitat--Washington (State)--Mount Rainier National Park; Trout--Climatic factors--Washington (State)--Mount Rainier National Park; Habitat (Ecology)--Washington (State)--Mount Rainier National Park--Management; Water temperature--Washington (State)--Mount Rainier National Park--Measurement; Glacial landforms--Temperature--Washington (State)--Mount Rainier National Park; Stream ecology--Washington (State)--Mount Rainier National Park; Aquatic habitats--Climatic factors--Washington (State)--Mount Rainier National Park; Fish populations--Monitoring--Washington (State)--Mount Rainier National Park; Endangered species--Conservation--Washington (State)--Mount Rainier National Park

Geographic Coverage

Mount Rainier National Park (Wash.); Carbon River (Wash.); White River (Pierce County and King County, Wash.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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