Estimates of Predator Consumption of Yellowstone Cutthroat Trout (Oncorhynchus clarki bouvieri) in Yellowstone Lake

ABSTRACT

We estimated consumption of Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri) by resident terrestrial predators and human anglers to place into context the potential predatory impact of exotic lake trout (Salvelinus namaycush) in Yellowstone Lake, Yellowstone National Park, Wyoming, USA. Estimates of consumption rates of piscivorous birds and mammals from the literature were combined with recent estimates of abundance of these predators in the park. Angling mortality was estimated by creel surveys from park management records. Results from a demographic model were used to estimate population size and age distribution of the cutthroat trout population. We estimated that terrestrial predators consumed approximately 7% of the trout population in the lake; angler mortality represented only 1–4% of the adult population. Piscivorous birds accounted for most (99%) of predator mortality, which was focused largely on juvenile trout. American white pelicans (Pelecanus erythrorhynchos) and grizzly bears (Ursus arctos) ate an estimated 5% of the adult trout spawning in streams. Depending on the ultimate size of the lake trout population, predation by introduced lake trout is expected to increase juvenile mortality by 13–67%. Consumption of young adult cutthroat trout by a large population of lake trout would effectively increase angling mortality by 50%. The resulting decline in the native cutthroat trout population is projected to have a significant effect on piscivorous birds, mammalian carnivores, and anglers in Yellowstone National Park.