Date of Award

Spring 2024

Rights

Access is available to all users

Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

Abstract

Seasonal prey abundance can drive predatory fishes to aggregate in areas of high prey density. This project aimed to determine whether Walleye (Sander vitreus) exhibit an aggregative predation response to larval White Sturgeon (Acipenser transmontanus) drifts in the Lake Roosevelt system which is a reservoir of the Columbia River in Washington State. Populations of sturgeon are threatened worldwide, and are in need of conservation research. Walleye are a popular nonnative piscivorous game fish that were accidentally or illegally introduced to Lake Roosevelt in the 1950’s. Walleye in this study were obtained by gillnetting during White Sturgeon pre-spawn, peak spawn, and post-spawn time frames based on historical timing trends in the reservoir. Walleye collections ran from May to October of 2023. A total of 667 Walleye were collected. Each stomach was dissected and prey items visually identified as fish had their DNA extracted, amplified, and sequenced to identify prey items to the species level. Of the 667 Walleye, 304 had prey items present. Diets included various invertebrates and 16 species of fish. Commonly encountered food items were sculpin, suckers, crayfish, and insects. Results show that no larval sturgeon were present in the stomachs, though one individual did consume a hatchery released juvenile sturgeon. Although there was a significant decline in catch rates in July, this appears to be associated with a slight change in capture methodology rather than Walleye distribution or abundance. Our data do not support an aggregative predation response by Walleye in response to the presence of larval White Sturgeon.

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