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Date of Award

Spring 2022


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Date Available to Non-EWU Users


Document Type

Thesis: EWU Only

Degree Name

Master of Science (MS) in Biology




The Clark Fork-Pend Oreille River basin of northeastern Washington and the Idaho Panhandle historically supported a robust metapopulation of Westslope Cutthroat Trout (WCT) Oncorhynchus clarkii lewisi, a western native salmonid of high cultural and economic value. The construction of impassible hydroelectric dams and smaller in-stream barriers has prevented the return of migratory WCT to spawning tributaries, likely leading to the fragmentation of this metapopulation over the last 100 years. One such impassible barrier is Albeni Falls Dam near Newport, Washington. Completed without fish passage capabilities in 1955, Albeni Falls Dam has been of interest as a site for restoring fish passage due to observations of large numbers of migratory salmonids below it. We attempted to determine the most likely spawning tributary of origin for 83 migratory WCT captured below Albeni Falls Dam by creating a genetic baseline representative of WCT populations within the Clark Fork-Pend Oreille River basin from upstream and downstream of the dam using 191 biallelic single-nucleotide polymorphism genetic markers. Our dataset included 124 collections and allowed us to examine population structure and hatchery influence across the study area and provided a robust tool for population assignment. Population assignment tests were conducted using the program RUBIAS. The self-assignment accuracy of our baseline dataset was greater than 95% depending on the geographic scale explored. All unknown migratory WCT were able to be assigned to a region within the study area—defined by dams and natural subbasin divisions—with a posterior assignment probability of at least 0.5 (50%). Of these, approximately 80% of migrants were assigned to tributaries upstream of Albeni Falls Dam with a posterior assignment probability of at least 0.9 (90%). Only one fish was assigned to a tributary downstream of Albeni Falls Dam. Our results indicate a significant need for fish passage facilities at Albeni Falls Dam. Passage at this barrier is likely to aid in reestablishing WCT metapopulation connectivity within the basin by allowing migratory individuals to complete their spawning migrations and make genetic contributions to populations upstream of the dam.