Date of Award

Spring 2019


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Document Type


Degree Name

Master of Science (MS) in Biology




Lake Trout (Salvelinus namaycush) were intentionally introduced to the Priest Lake system in 1925 with the intentions of creating a recreational fishery. As the Lake Trout population increased within this system, the native Bull Trout (Salvelinus confluentus) population began to decline. Possible negative impacts of Lake Trout on Bull Trout include direct effects such as predation, or indirect effects, such as resource competition. In this study our objective was to estimate the frequency of piscivory of Lake Trout from Upper Priest Lake and document any possible Lake Trout predation upon Bull Trout in the Upper Priest Lake system. We obtained Lake Trout samples from this system during annual gill netting, which is performed to suppress Lake Trout. We then performed stomach dissections to identify incidents of piscivory. Although Mysis shrimp were predominant prey items, 61 of 133 examined stomachs contained partially digested fish tissue. We then extracted DNA from these tissues and used a species DNA barcode located in the cytochrome oxidase 1 gene of the mitochondrion to identify said fragments. Out of a total of 61 samples 63.4% were identified as Lake Trout; 19.0% were identified as Pygmy Whitefish (Prosopium coulteri); 14.2% were identified as Kokanee Salmon (Onchohynchus nerka); and 1.5% were identified as Yellow Perch (Perca flavescens). Therefore, we suggest that the effects of Lake Trout on Bull Trout are not direct effects, but rather indirect effects such as resource competiton.