Wyoming reopened a blocked stream and cut non-native brook trout by 97%; native Snake River cutthroat trout then jumped more than 14-fold in just 3 years

A small stream near Jackson, Wyoming, shows how restoring fish passage can help native fish return to waters they once inhabited. In Game Creek, a road culvert blocked fish movement for decades, while non-native brook trout established themselves and displaced native Snake River cutthroat trout.

According to Wyoming Game and Fish Department’s Wyoming Wildlife magazine, replacing the culvert restored the connection with nearby Flat Creek, allowing cutthroat trout to return to Game Creek naturally. By 2024, the number recorded in surveys had risen more than 14-fold from the 2021 count, while a separate removal effort had reduced the brook trout population by 97 per cent.

How a road crossing cut off a native fish


The study also notes that Game Creek is south of Jackson and spans approximately six miles. The stream was previously known to be the spawning grounds of the Snake River cutthroat trout, which is the indigenous subspecies of trout in the upper Snake River drainage. Historical samples collected in 1953 and 1961 revealed that the entire population of trout in the stream consisted of cutthroat trout. The story took a different turn after the road construction included a new culvert for Game Creek that no longer allowed fish passage from Flat Creek. The brook trout species, which was introduced into the area by way of stocking programmes between 1941 and 1983, occupied the stream. By 2016, there were no more cutthroat trout observed upstream of the highway. The problem was not only the decline of the native species, but also the disruption of a migration route that gave fish access to good habitat. As a result, in 2018, the new culvert was installed to let the fish move under the highway to Game Creek.

Cutthroat trout numbers rose as brook trout declined

Department surveys showed the change. As reported in the magazine, the biologists counted five Snake River cutthroat trout in Game Creek in 2021. The number rose to 15 in 2022 and 16 in 2023 before climbing to 72 in 2024. It was a 14.4-fold increase in three years between 2021 and 2024. These are survey figures, rather than evidence that the total cutthroat trout population increased by the same factor. However, they indicate that native fish are returning to a stream where they had not been seen for many years.

Passage restoration was just one step of the management process. The Wyoming Game and Fish Department also started removing brook trout using electrofishing, which temporarily stuns the fish using electricity, allowing the crew to catch and remove them. Electrofishing has removed 97 per cent of the brook trout from Game Creek. Before the removal process, the department estimated 1,400 brook trout per mile.

A study in Transactions of the American Fisheries Society helps explain why managers target non-native brook trout when protecting cutthroat populations. It found that brook trout could displace native greenback cutthroat trout, with poor survival of eggs or young fish appearing to be an important factor. The findings concern a different cutthroat subspecies and stream system, but illustrate the competitive pressures that can arise when the species share habitat.

A return that also protects neighbouring waters

Flat Creek is home to a highly valued fishery of Snake River cutthroat trout, while Game Creek can be seen as a possible source of brook trout that might propagate to other areas. Lowering their population can reduce the threat to native fish elsewhere in the drainage. Moreover, the department has also tested another technique called YY, or Trojan male, brook trout.

These fish have two Y chromosomes and are expected to produce male offspring when they breed with wild female brook trout. Over time, the technology could transform an entire population into a male-only population and make it impossible for them to reproduce. The state of Wyoming has started stocking YY brook trout in Game Creek since 2024, along with continuing removal of wild brook trout. It is a relatively new management tool, and its effectiveness still needs to be tested in Wyoming.

The broader lesson from Game Creek is that restoring native fish populations does not always require reducing a competitor. A blocked culvert along the stream had disrupted the cutthroat trout’s route. The restoration of this path provided them with a chance to migrate back, while the removal of brook trout was meant to address another threat to their habitat. The rise in cutthroat trout from 5 in 2021 to 72 in 2024 is notable, although it remains unclear whether the fish can survive there long term.