Montana removed non-native brook trout and repaired mining-damaged White's Creek; the struggling native cutthroat trout population then grew at least sevenfold

In Montana, a small stream that had been battered by mining and overtaken by non-native fish became the setting for a conservation effort that produced a striking recovery. White’s Creek, in the upper Missouri River basin, once supported only a tiny remnant population of native westslope cutthroat trout. After years of removing competing brook trout and rebuilding the damaged stream habitat, researchers recorded at least a sevenfold increase in the native fish population.

According to a 2002 study published in the Intermountain Journal of Sciences, the recovery of native westslope cutthroat trout in Montana’s White’s Creek demonstrated the importance of combining habitat restoration with the removal of non-native fish. The population had fallen to about 80 fish measuring at least 75 millimetres long in the early 1990s, partly because of competition with brook trout and damage caused by historic mining. Between 1993 and 2000, researchers repeatedly removed brook trout using electrofishing, while restoration work repaired a mining-damaged section of the creek and a fish barrier was installed to prevent the non-native fish from returning upstream.

How mining and non-native fish pushed the trout towards decline


White’s Creek originates in the drainage area of White’s Gulch, east of Canyon Ferry Reservoir in Montana. The native westslope cutthroat trout (Oncorhynchus clarkii lewisi) in this stream faced two primary stresses: habitat degradation from historic dredge and placer mining, and invasion by non-native brook trout (Salvelinus fontinalis). Mining disturbed the stream habitat, altering the stream and valley-bottom channels and creating ponds and other disturbed areas. At the same time, brook trout were in competition with the native fish for food and living spaces. Together, these stresses resulted in the drastic decline of the cutthroat trout population, making it highly vulnerable.

More broadly, the problem reflected a larger conservation issue in the upper Missouri River Basin, where native westslope cutthroat trout had been eliminated from much of their range. While the species survived in some creeks, it was becoming increasingly important to protect them from habitat destruction and the presence of non-native species. Montana’s initiative in White’s Creek had two goals: removing brook trout, which threatened the native fish, and restoring habitat for the westslope cutthroat trout.

Removing brook trout and rebuilding the stream

The project started in 1993 with the electrofishing removal of brook trout from the stream. This process uses an electrical current in the water to temporarily stun the fish so they can be removed. The team did not remove brook trout throughout the entire drainage at once; instead, it worked in different parts of White’s Creek. The process turned out to be more challenging than anticipated. From 1993 to 2000, about 5,000 brook trout were removed.

As noted by the Intermountain Journal of Sciences, in 1995, the team also rehabilitated one kilometre of creek previously damaged by mining operations, including stream-channel and valley-bottom restoration. Eleven grade control structures were added to stabilise the channel, and woody material was introduced into the stream to enhance the habitat. In addition, a fish migration barrier was constructed to prevent the brook trout from migrating upriver and re-colonising the rehabilitated site. These efforts improved conditions for native fish populations.

The results also highlighted a limitation of the approach. A study published in the North American Journal of Fisheries Management examined the factors that may have contributed to non-native brook trout displacing native westslope cutthroat trout in Montana streams. The findings highlighted the complexity of interactions between the two species and the potential role of habitat conditions in shaping their distribution. This suggested that removing competing fish should be accompanied by efforts to maintain suitable stream habitat and prevent non-native fish from returning.

Native trout numbers rise, but long-term protection remains essential

The estimated number of westslope cutthroat trout increased substantially in the monitored sections of White’s Creek between the early and late 1990s. Although the increase varied between sections, the overall results indicated at least a sevenfold recovery, with the strongest gains recorded among young-of-the-year cutthroat trout. However, the scientists warned not to assume that the method would work everywhere. For one thing, White’s Creek is small and shallow, which made fish easier to capture than in larger, more complex watersheds. Removal took many years, and the scientists noted that the remaining native population was still vulnerable to reinvasion because its habitat range was limited.