Date of Award

Summer 2025

Rights

Access is available to all users

Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

Abstract

Salmonids express several different life histories from migrating to oceans and back or staying in their natal streams as a resident. Migratory individuals are a vital part of the overall success of populations due to the potential for increased genetic diversity and increased fecundity they offer over resident individuals. This research was completed in three basins including Priest River, Pack River, and Lightning Creek which are all connected to the Pend Oreille Basin and are important producers of Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi). Thirty-nine sites were sampled between the three basins. Results were compared between these tributaries that have been identified as high and low producers of migratory fish to find which variables seem to be the cause for out-migrating fish. Tributaries were backpack electrofished to collect fish densities and condition factor while drift samplers were used to capture invertebrates to determine prey density. Flow and temperature were measured to assess habitat quality. Previous research done by Keenan et al. (2024) showed that the maximum temperature of a tributary seemed to be the leading driver of out-migrating fish. The highest producer of migrant fish, Big Creek, reached hotter temperatures (19.13°C) and sustained them for a longer duration than any other tributary. Despite applying multiple modeling approaches, no single variable stood out as an indicator of migratory behavior during the 2024 sampling season. Future research should consider multi-year studies along with broader environmental monitoring in an attempt to better detect the ecological signals driving migratory behavior in Westslope Cutthroat Trout.

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