In an unprecedented move for native cutthroat trout conservation efforts in Wyoming, a historic release of 3,600 Trojan male brook trout took place in Game Creek in the upper Snake River drainage.

Brook trout, which displace native cutthroat due to competition, have inhabited Game Creek since the early 1950s. Brook trout were later documented in Flat Creek in 1976. As environmental conditions change, so can the potential for brook trout to expand and become a threat to native cutthroat.

Trojan male brook trout, sometimes called YY brook trout, have two Y-chromosomes, unlike normally produced males with an X and Y chromosome. These trout can be stocked into wild brook trout populations and reproduce with the wild fish, producing only male offspring. The stocking will continue until the population is 100% male and the trout no longer have the ability to reproduce. Without a reproducing population, the population will eventually die out, allowing for native cutthroat trout to be restored.

Game Creek is a source for brook trout populations to enter the mainstream Snake River, Flat Creek and its other tributaries. The removal of a source brook trout population may significantly reduce the opportunity for the species to become a problem in the Upper Snake River drainage.

“This is a huge step for our long-term goals in Game Creek,” said Diana Miller, Game and Fish fisheries biologist in the Jackson Region. “All the work that so many people have put into this project is contributing directly to the continued persistence of Snake River cutthroat trout in Flat Creek and the Snake River, and is something we all should be very proud of.”

Fisheries biologists in the Jackson Region will begin genetic testing of brook trout in Game Creek in 2026 to determine sex ratios. This will allow biologists to begin restoring native cutthroat in Game Creek while directly protecting cutthroat trout fisheries in the upper Snake River drainage.