Scubaism

A new study led by the University of Colorado at Boulder indicates biologists trying to save Colorado’s native greenback cutthroat trout from extinction over the past several decades through hatchery propagation and restocking efforts have, in most cases, inadvertently restored the wrong fish.

According to a sophisticated DNA analysis, five of nine “relic” populations of what biologists believed to be greenback cutthroat trout living in isolated pockets of the state actually are Colorado River cutthroat trout, a closely related subspecies, said lead author Jessica Metcalf, a researcher in CU-Boulder’s ecology and evolutionary biology department.

The new study, which included sequencing and analyzing mitochondrial and nuclear DNA, showed the majority of the greenback populations had been misidentified, and that the greenback cutthroat trout range is now restricted to just 11 miles of streams in several remote areas of Colorado.

The misidentification likely was caused by the stocking of fish in the late 1800s and early 1900s when railroads delivered hundreds of thousands of baby trout around the state of various species and subspecies for people to stock in local waters, said Metcalf.

Although greenback cutthroats were declared extinct in 1937 — victims of mining pollution, fishing pressure and competition from other trout species — several small populations were discovered in tributaries to the Arkansas River and South Platte River drainages in the 1950s, she said. Greenback cutthroats were added to the federal list of endangered species in 1978.

State and federal fish managers began taking eggs and sperm from what were believed to be surviving populations of pure greenback cutthroats in the 1970s, rearing them in hatcheries and returning them to native cutthroat habitat. The habitat — small streams and lakes — had been cleared of non-native fish species to heighten survivability of the greenbacks, said Metcalf.