Internal threats

Lake trout threaten native Yellowstone cutthroat

n 1994, a visitor to Yellowstone National Park, Wyoming, caught a big, nonnative fish in Yellowstone Lake. Subsequent investigations confirmed the presence of a lake trout (Salvelinus namaycush) population, which poses a significant threat to native Yellowstone cutthroat trout (Onchorynchus clarki bouvieri) and to the associated food chain. The park's only native trout is already reduced to 10% of its original range as a species. At least 42 species-including threatened grizzly bears and bald eagles, ospreys, pelicans, otters, black bears, and numerous waterfowl-prey or scavenge on native trout, which spawn in small, shallow tributaries and frequent the surface waters of the deep lake. The larger, carnivorous lake trout live and spawn in deep waters, making them unavailable to most fish eaters, including anglers. A decline in the native fishery would also have serious negative consequences for the regional economy and recreational anglers.

Previous long-term monitoring-and most angling- efforts targeted only native trout, and thus failed to discover the lake trout invasion for at least two decades. Experts recommend "industrial-strength" gillnetting to control lake trout and new monitoring programs to evaluate control efforts. This requires additional staff and equipment at a time of declining natural resource expenditures and, ironically, occurs just as the U.S. Fish and Wildlife Service (USFWS) closed its Fisheries Assistance Office, whose staff biologists had monitored and managed Yellowstone aquatic resources throughout the park's history.

In 1996, Yellowstone recruited a retired biologist, who volunteered as interim leader of fisheries management. One former USFWS biologist-enticed to change uniforms and stay with the park-traveled to the Great Lakes to learn about commercial gillnetting operations. According to lake trout experts, the good news is that our control efforts can be effective.

Last summer, biologists found a hotbed for lake trout spawning in the West Thumb of the lake. "Judas" fish were radio tagged and released so biologists can track them to gain information about how and where to control the invaders. That season, only two years after the discovery of the unwanted fish, 786 lake trout were caught by anglers and netting operations. The bad news is that the exotics, likely planted deliberately by some fan of "lakers," may already number in the tens of thousands. Eradication is unlikely; long-term control is imperative to prevent the native Yellowstone cutthroat from becoming endangered.

Other articles in the "Threats" chapter:

Threats and information

Demographics and resource preservation

The perennial push of exotic plants

Communication breakdown over drilling near Lechuguilla Cave

Historic water rights settlement averts threats at Zion

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This material is from Natural Resource Year in Review--1996, published by the National Park Service, U.S. Department of the Interior, in May 1997 (publication D-1182) http://www2./YearInReview/yir/yr_rvw96/chapter1/laketrou.htm
Last Update: 8/20/2002