In 2009, officials from the US Division of Wildlife Resources who were out searching for isolated populations of Colorado River Cutthroat Trout found something better—and far more perplexing.
Within a 1.2-mile stretch of Beaver Creek, which runs down the eastern flank of the La Sal Mountains near Moab, Utah, surveyors discovered a small, but genetically pure population of a subspecies of Cutthroat Trout known as the Greenback. The fish is not only rare among its fellow Cutthroats; it was heretofore unknown to Utah waters.
The natural history of the Greenback Cutthroat is fascinating! As a member of the genus Oncorhynchus, Greenback Cutthroat Trout trace their lineage back about 2 million years to Salmonid ancestors that chose to forego their return to the Pacific Ocean and instead pursued habitat further and further up the Columbia and Snake River drainages into the Green and Yellowstone River Basins. From here, cutthroat predecessors diversified into subspecies we know today: the Alvord, Bonneville, Humboldt, Lahontan, Yellowfin, Yellowstone, Colorado River, and, among others, the Greenback Cutthroat.
Greenbacks took a particularly arduous path to what is now their native home range. About 20,000 years ago, during the Pleistocene Epoch’s glacial maximum, Greenbacks hitched a ride via advancing ice sheets and their runoff, crossing eastward over the Continental Divide. And, historically, that’s where they’ve been found—east of the continental divide. However, in a 2014 summary report of a meeting among experts on the Greenback Cutthroat Trout’s whereabouts in Colorado, the US Fish and Wildlife Service says this about the fish’s home range: “Until recently, delineations of subspecies of cutthroat trout in Colorado were believed to follow geographic boundaries within the state, with greenback cutthroat trout on the eastern side of the Continental Divide and Colorado River cutthroat trout on the western side.” That seems to have changed.
Experts are at a loss as to how Greenbacks came to occupy the waters of Utah. Speculations abound from rogue fishermen stocking their favorite backwaters with favorite species from the Colorado Front Range to a remnant population of an ancient strand that may have ridden the glaciers all the way to La Sal runoffs. What’s even more perplexing is the population’s pure genetic makeup. Cutthroat Trout hybridize easily with other fish; but the Beaver Creek population hasn’t. One reason may be the creek’s inaccessibility. Disease and non-native trout haven’t threatened the resident Greenbacks; and so they have lived on undisturbed, unadulterated, and, until about a decade ago, unknown to their human counterparts. This gives the wildlife conservation community some hope for the fish’s viability moving forward.
Greenbacks currently only occupy roughly 1% of their historic native range and were once thought to be extinct altogether. This hardy and adventurous fish refuses to call it quits, though. Who knows, maybe the valiant reclamation of its old territory has already begun along so many other inaccessible and unadulterated creek beds.