Abstract
Yellow Perch (YEP) Perca flavescens was first encountered in Lake Cascade in 1957. Since its introduction, the abundance of YEP in Lake Cascade has been highly variable. Historically, declines in YEP abundance were attributed to predation by Northern Pikeminnow (NPM) Ptychocheilus oregonensis. As a result, about 1.4 million NPM have been removed from Lake Cascade since 1958. In the 1990s, a novel predator, Smallmouth Bass (SMB) Micropterus dolomieu, became established in Lake Cascade. Although YEP abundance has been high and currently supports a world-class fishery, the Idaho Department of Fish and Game has documented variable YEP recruitment in recent years, indicating that another population decline may be imminent. An investigation into the food habits of YEP, SMB, and NPM was initiated to better understand the importance of juvenile YEP to predator diets. In Lake Cascade, gill nets were deployed monthly from April 2022 to May 2023. In total, stomach contents were extracted from 1,099 YEP, 440 SMB, and 980 NPM. Food habits varied by season and predator length, but YEP was a primary prey item of all study species. The energetic contribution of YEP to YEP varied from 10% to 80% across seasons. Smallmouth Bass (40% of total consumption) consumed fewer YEP than either YEP (50% of total consumption) or NPM (60% of total consumption). Northern Pikeminnow from 500-600 mm consumed the highest average number of YEP (5 YEP/NPM). Energetic contribution of YEP to NPM diets was highest in spring-2023 yet NPM consumed the highest average number of YEP in July. Bioenergetics modeling estimated per capita consumption of YEP was 6.0 kg for YEP, 3.4 kg for SMB, and 9.9 kg for NPM. In total, estimated consumption of all study species was as high as 37% of the estimated total number age-0 YEP produced. Northern Pikeminnow appeared to consume a disproportionately large number of YEP compared to YEP and SMB. My study provides important information on the predation of YEP in Lake Cascade. Further, my work will bolster a growing body of research on the food habits of and interactions between native and non-native predators in western reservoir systems.