Significance of the 10-Million-Year History of Cutthroat Trouts

A deeper time perspective might be important to understanding and managing Cutthroat Trouts. Ancestral western trouts ranged from the central Mexican Plateau to the extreme North Pacific, and like Pacific salmon, diversified in major drainages millions of years before the ice ages. Cutthroat Trouts split from Rainbow and Redband Trouts more than 10 million years ago. They were adapted to a variety of coastal streams in the north and mountain habitats in Columbia, Missouri, Colorado, and Rio Grande headwaters in the Rocky Mountains. They colonized ancient lakes and streams of the Great Basin, the oldest representative being the 10-million-year- old Truckee Trout of Nevada. During the Pleistocene, these trouts lived at elevations of 4600 ft in Nevada, 5000 ft in Utah, 6000 ft in New Mexico, 6600 ft in Wyoming, and 8800 ft in Colorado. They survived extremes of glaciation and interglacials in fluvial and lacustrine habitats. Bob Behnke pointed out the ecological replacement of Cutthroat Trout by Redband Trout in the lower Snake River drainage. Scores of fossil collections now show that for 5 million years Cutthroats did not tolerate ecological or genetic competition from Redband Trout.