CPW introduces Trojan Male brook trout in a historic effort to protect native cutthroat trout in Colorado

09/27/24

Rachael Gonzales
Northwest Region Public Information Officer
970-773-8587 / [email protected]
Twitter: @CPW_NW

CPW introduces Trojan Male brook trout in a historic effort to protect native cutthroat trout in Colorado

HOT SULPHUR SPRINGS, Colo. - On Tuesday, Sept. 17, in an effort to restore native cutthroat populations in the headwaters of the Williams Fork River, Colorado Parks and Wildlife stocked 480 Trojan male or YY brook trout into Bobtail and Steelman creeks.

“This is a pretty historic moment for Colorado and native cutthroat trout restoration across the state,” said CPW Aquatic Biologist Jon Ewert. “This is a combination of both the hard work and dedication of CPW biologists current and retired.” 

“This is yet another example of the groundbreaking work done by CPW biologists and researchers to preserve native species,” said George Schisler, CPW Aquatics Research Section Chief. “While Bobtail and Steelman creeks are the first to be stocked with YY brook trout, they will not be the last. This is just the first of many for Colorado.”

In 2010, an alarming number of non-native brook trout were discovered after completing a fish survey in the headwaters of the Williams Fork River. While it is unknown when brook trout invaded these creeks, it was evident the thriving brook trout had nearly decimated the native cutthroat population over time.

Cutthroat trout found within these two creeks are some of the highest-valued native cutthroat populations in the headwaters of the Colorado River basin. Considered a species of special concern in Colorado, this subspecies of trout is genetically pure and naturally reproducing. 

“In 2011 we found 123 cutthroat trout combined in both creeks. Today, after 13 years of hard work by dedicated biologists we are seeing a little more than 1,400 cutthroats in these creeks,” said Ewert. 

Trojan male brook trout are often called YY because they have two Y chromosomes, unlike wild males with an X and Y chromosome. These trout are stocked into wild brook trout populations and reproduce with the wild fish, producing only male offspring. Without a reproducing population (male and female fish), the brook trout will eventually die out, allowing for native cutthroat trout to be restored.

Colorado Parks and Wildlife will continue to stock both streams with YY brook trout over the next several years to sustain the number of Trojan males in the population, eliminating the production of female brook trout in the creeks. 

To learn more about Trojan male brook trout and cutthroat trout restoration project in the Upper Williams Fork drainage, read our latest Colorado Outdoors Online Magazine article.