The Yellowstone Lake crisis: confronting a lake trout invasion

Varley, John; Schullery, Paul

Yellowstone Lake is home of the premier surviving inland cutthroat trout fishery in North America. This fishery is threatened with destruction by illegally introduced lake trout, which were discovered in 1994. The lake trout are known to exist in at least four and possibly as many as six age groups, proof of a relatively small but reproducing population (Fig. 1). The older age groups are now able to reproduce, and the lake trout population will almost certainly grow rapidly. The discovery of these non-native lake trout in Yellowstone Lake caused great alarm among fisheries biologists throughout the greater Yellowstone area because of the lake trout’s reputation for displacing species such as cutthroat trout in other western lakes. Park administrators sought to verify the “doomsday” opinion of local biologists by arranging an assessment of the situation by United States and Canadian specialists in population dynamics and lake trout biology. The experts convened an information-sharing workshop in February 1995, and concluded that the lake trout population in Yellowstone Lake is likely to expand and cause precipitous decline in the cutthroat trout population. The majority view was that the cutthroat trout are likely to decline to 10-20% of present abundance. These percentages translate to a decline from an estimated 2.5 million trout of catchable size at present to 250,000-500,000 at some time in the foreseeable future. Except for its strongholds in the upper Yellowstone River area, the Yellowstone cutthroat trout is imperiled. Human activities have already reduced its range to 15% of its historic distribution. The appearance of lake trout in Yellowstone Lake has ominous implications for the continued viability of the Yellowstone cutthroat trout as a subspecies. The predicted decline of Yellowstone cutthroat trout will destroy the world-famous fisheries in the lake and its tributaries, including the storied fishery in the Yellowstone River between the lake and the Upper Falls; this latter fishery gained international prominence in the 1970s as the site of pioneering advances in catch-andrelease fishing, and remains one of the world's premier destinations for trout fishermen. For nearly 150 years, the lake itself has developed its own superlative reputation as a “trout catchery.” Though a lake trout fishery will evolve in the lake consonant with the cutthroat decline, it will be a highly specialized fishery of interest only to a comparatively few anglers and will not occur at all on the rivers and streams. The replacement fishery will in no respect (ecologically, economically, or socially) replace the fisheries it destroys. The cutthroat trout decline will also cause severe disruption in the food supply for two species listed under the Endangered Species Act—the threatened grizzly bear and the endangered bald eagle—and will likewise affect many species of special concern, including the white pelican, otter, black bear, mink, osprey, and loon; an estimated 42 species of mammals and birds in all. Grizzly bear, white pelican, and osprey abundance at Yellowstone Lake, and perhaps other species as well, are all correlated with the abundance of Yellowstone Lake cutthroat trout. Because of pronounced differences in the habits and habitat uses of lake trout and cutthroat trout, the lake trout will not serve as a replacement food source for these affected species of mammals and birds.