Date of Award

Spring 2026

Rights

Access is available to all users

Date Available to Non-EWU Users

2026-07-01

Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

First Advisor

Paul Spruell

Second Advisor

Jenifer Walke

Third Advisor

Nigel Davies

Abstract

The Westslope Cutthroat Trout (Oncorhynchus lewisi) is a native species of salmonid that holds both cultural and ecological significance in the Idaho Panhandle region of the United States. Within this region, the Priest River is a major contributor of migrant Westslope Cutthroat Trout to the Clark Fork Pend Oreille basin. This study aimed to estimate the proportion of juveniles that have at least one migrant parent, illustrate gene flow using juvenile half sibling relationships, and showcase varying levels of spawning success using juvenile full sibling relationships. Sampling of juvenile individuals occurred in 11 tributaries of the Priest River over the span of five years (2021-2025). Migrant individuals were collected from the mainstem Priest River, shoreline of lake Pend Oreille, and Pend Oreille River. Migrant and juvenile individuals were genotyped at 191 Single Nucleotide Polymorphism’s (SNP’s). These data were used to conduct familial relationships using COLONY. This program uses a maximum likelihood method to infer familial relationships, parent-offspring relationships between migrants and juveniles, full-sibling, and half-sibling relationships between juveniles. We found five tributaries in which recruitment from migratory individuals ranged from 5.4 - 21.4%. Four of those same five tributaries are also suggesting varying levels of gene flow amongst each other, as inferred using half-sibling data. The number and size of full-sibling families varied between tributaries, indicating various levels of spawning success. Half-sibling relationships occurred both within and between tributaries, with the proportion of between tributary pairs ranging from 10.8 - 65.9% of the individuals in a tributary with a half-sibling identified. These findings suggest that some number of tributaries in the Priest River are reliant on migratory individuals in terms of both gene-flow and recruitment in the Priest River. Management actions should be implemented to protect and improve the habitat in these tributaries. These actions will maintain the metapopulation function and the stability of Westslope Cutthroat Trout in the Priest River basin.

Download

Share

COinS