YELLOWSTONE NATIONAL PARK, Wyo. — When a young angler casting from fishing guide Tom Hansen's boat reeled in a mottled blue-green fish in July, Hansen knew immediately it was not a native cutthroat trout for which Yellowstone Lake is famous.
While Yellowstone cutthroats carry a distinctive red slash below their mouths, this fish had none.
"I knew it was something that didn't belong," recalled Hansen, a teacher in Pittsburgh when he is not guiding anglers in Yellowstone National Park's largest lake.
Biologists have since confirmed that the fish was a lake trout, or Mackinaw, an intruder indeed. In following months, anglers and federal netting crews nabbed more of the exotic fish that experts now fear may wreak havoc on the largest intact ecosystem left in the Lower 48 states.
Lake trout pose a danger not only because they gobble smaller cutthroats, but also because by doing so, they could send shudders through the food chain that sustains wildlife from grizzly bears to birds of prey.
"This may be the beginning of a major change in the traditional picture of the Yellowstone ecosystem," U.S. Fish & Wildlife Service biologist Lynn Kaeding says as his motorboat skims the surface of the icy blue lake on a sunny but cold fall day.
Set amid snowy peaks at an elevation of 7,733 feet, Yellowstone Lake is the last stronghold of the Yellowstone cutthroat--squeezed from 90% of its original range by human development and alien predators. The national park's cutthroat may be the largest undisturbed population of native trout left in the world.
Even the first military caretakers of Yellowstone safeguarded local cutthroat from big and voracious lake trout, native only to Canada and the Great Lakes.
Government agencies brought the Eastern species to many Western waters, including empty lakes in Yellowstone, in a kind of Johnny Appleseed approach to fish management at the turn of the century. But they always spared 85,000-acre Yellowstone Lake and its prized cutthroat.
Catches this past summer, however, proved lake trout have finally invaded the largest high-altitude lake on the continent. There are no natural links between Yellowstone Lake and nearby waters containing lake trout, so rangers suspect renegade anglers seeking a new challenge surreptitiously planted the big fish.
Calling the action "an appalling act of environmental vandalism," Yellowstone managers are offering a $10,000 reward for information leading to the conviction of those responsible.
