<P> The Rocky Mountains are home to a number of coldwater fish in the trout and salmon families, including rainbow trout, bull trout, lake trout, cutthroat trout, brown trout, brook trout, golden trout, mountain whitefish, Arctic grayling, and Dolly Varden . Many of these, however, are introduced, such as rainbow, brown, and brook trout . </P> <P> Colorado River cutthroat trout were once abundant in mountainous tributaries of the Green and Colorado rivers, but non-native brown, brook, and rainbow trout had displaced them by the 1930s . They still survived in some isolated pockets, however, and these populations have been used to restore the cutthroats to many areas in their historic range . One of the largest strongholds was, and is, Trappers Lake in Colorado's Flat Top Mountains . However, in 1984, brook trout invaded because a flood washed them downstream from nearby Crescent Lake . By 2003, brook trout comprised 40 percent of the lake's fish population . Brook trout have an advantage over cutthroat trout because they spawn in fall . By the time Colorado River cutthroats hatch in August, brook trout fingerlings may be able to eat them . Colorado Parks and Wildlife is controlling their population with large nets and selective removal . </P> <P> The Greenback cutthroat trout was original thought extinct in 1937 . However, in the 1950s, scientists found putative greenbacks on the eastern slopes of the Front and Sawatch ranges in Colorado . A campaign by Colorado Division of Wildlife and several federal agencies introduced these fish to many areas in the trout's former range . In 1996, it was designated as Colorado's state fish . Then in 2012, researchers at the University of Colorado found that the only pure population of these fish was in a small stream in the Arkansas River basin, outside their native range . Since then they have been reintroduced to Zimmerman Lake on the edge of northern Colorado's Neota Wilderness and Sand Creek in Red Mountain Open Space north of Fort Collins . </P> <P> Yellowstone Lake in Yellowstone National Park, Wyoming, is the site of the most recent catastrophic species invasion . The Washington Post reported that the nonindigenous lake trout, a native of the Great Lakes, had been insidiously introduced into one of the nation's premier fisheries . The native Yellowstone cutthroat trout may not compete well with lake trout because lake trout eat cutthroat trout . The potential ecological repercussions are staggering . If populations of cutthroat trout continue to decline, grizzly bears could lose an important posthibernation food because the native cutthroat trout spawn in the streams and are easy prey for the bears, whereas the nonindigenous lake trout spawn in deep water . The National park Service has begun an aggressive attempt to eradicate the invasive fish by hiring commercial fishing crews, and have removed over 1.7 million with gill nets . It is estimated that for every lake trout removed from Yellowstone Lake, 41 cutthroat trout are saved . So far the cutthroat trout have shown modest signs of recovery . However, other threats to the trout remain, such as whirling disease, brought from Europe by nonnative brown trout . </P>

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