Greenback Cutthroat Trout - Natural History

Natural History

The cutthroat trout is thought to have evolved over the past two million years from other Oncorhynchus species which migrated up the Columbia and Snake river basins to the Green and Yellowstone river basins. Within the past 20,000 years, a population which crossed the Continental Divide during the most recent Ice Age gave rise to the greenback cutthroat. The greenback cutthroat trout today is found east of the Continental Divide in the cold, clear foothill and mountain waters of the Arkansas and South Platte Rivers. Although it was common in the late 19th century, ranging along the Front Range from Wyoming to New Mexico, it began to decline when settlers arrived in the area. Mining in its native river basins led to sediment and toxic runoff in the water. These factors, along with water diversion for agriculture and overfishing, led to the decline of many greenback cutthroat trout populations.

The introduction of non-native species such as brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (O. mykiss) was also detrimental to the greenback cutthroat. The former two species competed with greenback cutthroats while the latter hybridized with it, creating cutbows. Other subspecies of cutthroat were introduced to greenback habitat, further damaging populations due to hybridization.