Abstract
Adfluvial Westslope Cutthroat Trout Oncorhynchus clarkii lewisi populations have declined significantly since the 1900s in Coeur d'Alene Lake, Idaho. The Coeur d'Alene Tribe has an intense Passive Integrated Transponder (PIT) tagging program and has reported poor juvenile to adult return rates, which is hypothesized to be a result of predation by nonnative species, such as Northern Pike Esox lucius and Smallmouth Bass Micropterus dolomieu. Sampling occurred on 138 days and 15,645 individual fishes representing 24 species were captured. The population structure and dynamics of Northern Pike and Smallmouth Bass were similar across sampling locations. After pooling data for Coeur d'Alene Lake, growth of Northern Pike and Smallmouth Bass was compared using meta-analysis to other populations across their distributions. The potential effect of predation by Northern Pike on Westslope Cutthroat Trout was evaluated with bioenergetics modeling. Northern Pike (i.e., 2008-2011 year classes) consume an estimated 5,641 Westslope Cutthroat Trout annually from the four sampling locations (i.e., Cougar, Wolf Lodge, Windy bays, Benewah Lake) in Coeur d'Alene Lake.