![]() Because of the lack of barriers in the lower reaches of most drainages, nonnative fish have been dispersing upstream and have replaced, or threaten to replace, cutthroat trout. Rainbow trout pose the additional threat of hybridizing with cutthroat trout. In other waters, brown, brook, and rainbow trout all compete with cutthroat trout for food and habitat. In Yellowstone Lake, lake trout are a major predator of cutthroat trout. Habitat remains pristine within Yellowstone National Park, but nonnative fish species pose a serious threat to native fish. Life history diversity within an ecosystem helps protect a population from being lost in a single extreme natural event. ![]() Some populations live and spawn within a single stream or river (fluvial), some live in a stream and move into a tributary to spawn (fluvial-adfluvial), some live in a lake and spawn in a tributary (lacustrine- adfluvial), and still others live in a lake and spawn in an outlet stream (allacustrine). The variety of habitats resulted in the evolution of various life history types among Yellowstone cutthroat trout. One possible such passage in the Yellowstone area is Two Ocean Pass, south of the park in the Teton Wilderness. While the Yellowstone cutthroat trout is historically a Pacific drainage species, it has naturally traveled across the Continental Divide into the Atlantic drainage. Yellowstone Lake and the Yellowstone River together contain the largest inland population of cutthroat trout in the world. ![]()
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