Effects of introduced lake trout on native cutthroat trout in Yellowstone lake. Ecol.l Appl

Abstract. The establishment of a reproducing population of nonnative lake trout (Sal-velinus namaycush) poses a serious threat to the integrity of the Yellowstone Lake eco-system, particularly to the indigenous cutthroat trout (Oncorhynchus clarki bouvieri). We used standard fisheries techniques to quantify the population-level impact resulting from this introduction, while the U.S. National Park Service (NPS) developed a program to control their numbers. Lake trout diets, thermal history, growth, and size structure were incorporated into a bioenergetics model to estimate the predatory impact of introduced lake trout and to evaluate the effectiveness of the NPS lake trout control program. Population size structures were estimated from catches of fish in gill nets that were corrected for mesh size selectivity. Lake trout abundance was estimated using virtual population (cohort) anal-ysis, and cutthroat trout abundance was estimated using hydroacoustics. Juvenile cutthroat trout were highly vulnerable to predation, and lake trout preyed on cutthroat trout that averaged 27–33 % of their body length. Based on our model, an average piscivorous lake trout consumed 41 cutthroat trout each year. During 1996, the piscivorous lake trout pop-ulation consumed an estimated 15 metric tons of cutthroat trout (129 000 fish) composin