Genetic Boost Raises Colorado Cutthroat Trout by 1,000

Colorado Parks and Wildlife sees success in using 'Trojan male' brook trout to restore native species

Published on Mar. 10, 2026

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Colorado Parks and Wildlife reported positive results in September 2025 from a project using 'Trojan male' brook trout to restore native Colorado River cutthroat trout. Biologists documented more than 1,300 native trout in two Grand County creeks where invasive species are being phased out through genetic intervention.

Why it matters

The Trojan male method is a novel approach to eliminating invasive fish species and allowing native populations to recover. This project in Colorado represents a major milestone in the use of this genetic technique for fish restoration, with potential applications for managing other problematic non-native species like common carp.

The details

The survey took place in Bobtail and Steelman creeks, where researchers introduced YY brook trout - males with two Y chromosomes - to eliminate the invasive wild brook trout that compete with native cutthroat trout. During the two-day effort, the teams recaptured and released more than 130 YY brook trout while removing a similar number of wild brook trout. Staff documented more than 1,300 cutthroat trout across the two creeks.

  • In 2011, researchers only observed 123 cutthroat trout in the two creeks.
  • In 2024, CPW first stocked YY brook trout into Bobtail and Steelman creeks.
  • In September 2025, the survey documented the positive results of the restoration project.

The players

Colorado Parks and Wildlife

The state agency responsible for managing Colorado's wildlife and natural resources.

Jon Ewert

The Hot Sulphur Springs area aquatic biologist for Colorado Parks and Wildlife.

Dr. George Schisler

The aquatics research section chief for Colorado Parks and Wildlife.

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What they’re saying

“We continue to see positive results for our native cutthroat trout population from the brook trout removal efforts in these two creeks.”

— Jon Ewert, Hot Sulphur Springs area aquatic biologist (WesternSlopeNow.com)

“In 2024, we did something historic for fish restoration in Colorado when we first stocked YY brook trout into Bobtail and Steelman creeks.”

— Dr. George Schisler, Aquatics research section chief (WesternSlopeNow.com)

What’s next

CPW plans to continue stocking YY brook trout into Bobtail and Steelman creeks over the next several years to completely eliminate the invasive brook trout populations.

The takeaway

This project demonstrates the potential of the Trojan male genetic technique to effectively restore native fish species by eliminating invasive competitors. The success in Colorado could lead to expanded use of this innovative approach to manage other problematic non-native species in the future.