Finding of Non-Native Trout in Yellowstone Leaves Officials Reeling : Ecology: Biologists fear that the cutthroat population could be wiped out if the larger and more aggressive lake trout become established. That, in turn, could deprive grizzlies of food.

When 11-year-old Danielle Marie McCain of Phoenix reeled in her line during a family fishing outing on Yellowstone Lake July 30, she caught more than just a 1-pound lake trout on her No. 5 Blue Fox lure.

She also landed what is potentially a major crisis for one of the Rocky Mountain West’s premier native fisheries.

McCain’s catch--a trout species not native to Yellowstone Lake--stunned federal officials who have spent years protecting and nurturing the Yellowstone cutthroat trout population, which inhabits the 86,000-acre lake and many of its tributary streams in the heart of America’s oldest national park.

Fish biologists fear that the Yellowstone cutthroat population, one of the few robust native fisheries in the northern Rockies, ultimately could be wiped out if the larger and more aggressive lake trout become established.

The problem, reduced to its basics, is that lake trout get big and eat cutthroat trout. “Freshwater sharks” is the description of one fish biologist. As large as it is, Yellowstone Lake may not be big enough for both of them.

Never mind whether a fish has light spots on a dark background and a deeply forked tail--like the lake trout, whose original habitat was the Great Lakes--or dark spots on a light background and a distinctive red slash on its throat--like the smaller, native Yellowstone cutthroat. Isn’t a trout a trout?

For both practical and philosophical reasons, the answer is no.

For one thing, the Yellowstone cutthroat occupies a special and important niche in the rich biological world of the park, a 2-million-acre preserve stretching across the Wyoming-Montana border that is home to big herds of elk and bison and a number of threatened and endangered species.

Rigorously managed by the U.S. Fish and Wildlife Service since the 1970s, the cutthroat fishery has rebounded from overfishing to become a key part of the food chain for the park’s bald eagles, osprey, otters and grizzly bears.

Every spring, for example, the lake’s cutthroat trout head upstream into 68 of the lake’s 124 feeder streams to spawn. Once in these streams, they become a virtual buffet for grizzly bears that recently have emerged from their alpine dens and come to the low country in a frantic search for protein after their long hibernation.

If lake trout take over, the bears--on the list of threatened species since 1975--would lose an important food source, because the invaders spawn deep in the lake far out of grizzly range.

Yellowstone Lake’s cutthroat fishery is “unique in the world,” said Jack Stanford, director of the University of Montana’s Flathead Lake Biological Station.

Because the lake is fed by thermal vents, it is unusually productive for an alpine lake and produces several distinct strains of cutthroat. “You see high diversity within a single genetic unit,” Stanford said. “You could hardly think of (a native fishery) that is more important.”

Preserving the native cutthroat is also part of the National Park Service’s mission of protecting naturally occurring fish, wildlife and plant populations. “This was the native trout,” said Lynn Kaeding, the U.S. Fish and Wildlife Service official in charge of maintaining the park’s fisheries. “When Lewis and Clark came out here, that was the fish they encountered.”

To conservationists, the threat to Yellowstone cutthroats is just part of a larger story of the steady decline of native fisheries in the West. Montana remains a magnet for sport fishermen, with its storied blue-ribbon trout streams like the Madison, Yellowstone and Big Hole Rivers. But the brown and rainbow trout that inhabit those waters and are prized by fly fishermen are the descendants of imports.

“Montana gets all this ink for its trout fisheries,” said Bruce Farling, executive director of the Montana chapter of Trout Unlimited, a fish-conservation group. “But it’s for the brown trout, which came from Europe, and the rainbow, which came from the Pacific coast.”

The reality for native fish, said Farling, is that many are facing the threat of extinction as habitat is lost and degraded by development, logging and ranching, and as they are crowded out by alien fish.

Among the native Montana fish in various degrees of trouble are the bull trout, now found in less than half of its historical range; the west slope cutthroat, the fluvial grayling and the white sturgeon, recently placed on the endangered species list.

The same story holds throughout most of the West, from the precipitous decline of many salmon species in the Northwest to the perilous status of squawfish and other species on the Colorado.

“Native fish in general are at great risk,” said Stanford. “There are very few, if any, success stories of recovering native fish. . . . The overwhelming culprit is the introduction of non-native species.”