These Waters Aren’t Deep Enough for the Both of Us: A Brown and Cutthroat Trout Showdown

Guest Blogger: Madison Richardson

The following guest post was voted best in the class for an undergraduate assignment on communicating science from Cal Poly Humboldt’s Fall 2021 Fish Conservation and Management course taught by Dr. Andre Buchheister. The assignment required students to find a peer-reviewed article on a fisheries management topic that interests them and to communicate the issue in a blog format to a general audience.

Yellowstone cutthroat trout, the prized jewel of Yellowstone swimming off into the sunset. Photo credit: Clayton 2021.

A national treasure within a national treasure, the iconic Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) is found exclusively within the United States’ first national park that shares its name. This beautiful fish is as beautiful as the place it calls home with golden-brown and olive hued body littered with medium-large black spots toward its posterior and the signature cutthroat red slashes on the lower jaw. Yellowstone cutthroat trout are a keystone species; they feed a myriad of predators including grizzly bears, river otters, and several species of birds (NPS 2009). These trout are crucial in delivering nutrients from Yellowstone Lake back into the ecosystem when returning from their spring spawning migration in the lake’s tributaries (Bigelow et al. 2003). Not only do these fish provide value to the park’s ecosystem, where an estimated biomass of 100,000 kg of cutthroat trout are consumed by avian predators annually (Gresswell 2009), they also provide value to its economy as well. As a hot commodity only found in Yellowstone, the cutthroat trout’s recreational fishery within the park provides an approximated $36 million value to the regional economy (Bigelow et al. 2003). However, the national park is in danger of losing this prized jewel to the invasive brown trout.

Big Bad Brown Trout

An outlaw brown trout rustled up by a fisherman in Yellowstone’s Madison River (Photo credit: Juracek 2011).

 Hailing from Europe and parts of Asia, the brown trout (Salmo Trutta) was brought to North American lakes and rivers for social and economic benefits driven by sport fishermen (Al-Chokhachy and Sepulveda 2019). The brown trout is a notoriously elusive and difficult fish to wrangle, and the opportunity to catch these outlaws draws in anglers from across the globe every year. This voracious species is not only aggressive on the fly, but within the food web as well. Brown trout are extremely successful invaders to any watershed they are introduced to because of their abilities to outcompete, predate, and displace native species. The diets of native trout and brown trout are much the same, except, brown trout consume larger prey, including juvenile fishes (Budy et. al 2018). A small-scale experiment on the interactions between brown trout and native trout revealed that about 20% of adult native trout mortality is caused by the predation of adult brown trout, (Budy et. al 2018). Brown trout are found in low elevation waters, while native trout are found in higher elevation waters (Budy et. al 2018). Claiming prime territory at lower elevations and chasing the cutthroats out of Dodge, the brown trout force the cutthroats to higher elevation streams where there are slim pickings.

A New Outlaw in Town

The big bad brown trout first swam into the town of Yellowstone National Park in the early to mid-1900s as a recreational sport fish (Al-Chokhachy and Sepulveda 2019). The idea was to draw in more fishermen and women for both browns and cutthroats to help boost the local economy. However, a simple introduction of these outlaws resulted in a drastic population shift for the Yellowstone cutthroat trout.

Tributary Trials

To evaluate the interspecific relationship between the introduced brown trout and native Yellowstone cutthroat trout, Al-Chokhachy and Sepulveda (2019) compared two creeks in the Duck Creek tributary of the Yellowstone River, Henry’s Fork and East Fork. Comparing surveys from this area between the 1980s and 2010s revealed that the outlaw brown trout had taken the reigns from the Yellowstone cutthroat trout and commanded the waters of the Duck Creek watershed in greater populations.

Duck Creek, Montana where the study of allopatric and sympatric effects on Yellowstone cutthroat trout took place. The white circles represent the allopatry sites (Yellowstone cutthroat only) and the gray circles represent the sympatry sites (with Brown trout; Figure from Al-Chokhachy and Sepulveda 2019).

To better understand the direct impacts of brown trout on Yellowstone cutthroat trout, Al-Chokhachy and Sepulveda (2019) set up their study to examine allopatric and sympatric populations. Allopatry refers to the two species living in separate locations, and sympatry refers to the two species existing in the same location together. Montana Fish, Wildlife, and Parks reintroduced an allopatric cutthroat trout population by transporting fertilized Yellowstone cutthroat trout eggs above a waterfall, a natural, impassable fish barrier in an area where, historically, the Yellowstone cutthroat trout were the only naturally occurring fish. Below the waterfall, Yellowstone cutthrout lived in sympatry with brown trout. In a paired design, Al-Chokhachy and Sepulveda (2019) selected six sites for their study, three below the waterfall where they studied growth, diet, and survival of brown trout and cutthroat trout in sympatry and three above the waterfall where they studied growth, diet, and survival of Yellowstone cutthroat trout in allopatry.

After several years of study, Al-Chokhachy and Sepulveda (2019) confirmed that the big bad brown trout were trying to run the poor ole’ Yellowstone cutthroat trout out of town. Brown trout significantly hindered the growth rate of length and mass of sympatric adult and juvenile Yellowstone cutthroat trout). The allopatric Yellowstone cutthroat trout, whom are those not terrorized by the outlaw brown trout had growth rates almost twice as large as the sympatric Yellowstone cutthroat trout. The most alarming results from the study found that the Yellowstone cutthroat trout in sympatry with brown trout where 2.5 times smaller than those in allopatry. Over time, the average size of sympatric Yellowstone cutthroat trout was smaller and smaller because of their inability to compete with the voracious brown trout.

Bounty on Brown Trout

Since the arrival of the big bad brown trout to Yellowstone National Park in the mid-1900s, it has outcompeted the native Yellowstone cutthroat trout, displaced it to higher elevation reaches, stunted its growth, and reduced overall numbers of individuals. Brown trout are on their way to taking over town and the Yellowstone cutthroat trout may be on their way to extinction if no one rounds up those alien outlaws.

Beyond the park boundaries, there is no other place on Earth where Yellowstone cutthroat trout occurs naturally. Allowing brown trout to stay and dominate the waters of the park aids in the decline of this iconic fish. Although brown trout provide social and economic benefits as a sport fish, Yellowstone cutthroat trout are priceless to the national park. However, it isn’t too late for Yellowstone cutthroat trout. These natives can return to the lower waters from their upper reaches if fisheries managers implement strategies to control the brown trout populations. From the study on the Duck Creek watershed, we have already seen that barriers, like the waterfall, effectively hinder the movement of brown trout upstream and give Yellowstone cutthroat trout the opportunity to thrive in these isolated areas. Another method is to use a weir which is a barrier built across the width of a river that raises or regulates the flow of water, to trap and prevent upstream migrating brown trout from passing. Angling is another management strategy. In an upstream stretch of the Kootenai River in Montana, there are mandatory kill fishing regulations on brown trout because they were illegally introduced and are feared to impact the native populations of bull trout (Salvelinus confluentus) and rainbow trout (Oncorhynchus mykiss) (Chrestenson et al. 2018). The Montana FWP could follow suit from the practices in the Kootenai River, by increasing the angling limit on brown trout, and even incentivize anglers to catch and remove brown trout from Yellowstone National Park. If these strategies can be implemented over the course of several years, the Yellowstone cutthroat trout population may return in greater numbers and regain their homestead that is now controlled by the outlaws.

We have the power to reverse the effects of mistakes made by the people that came before us but only if we choose to do so. This issue is no longer a management obligation, but a moral obligation as well. We may not have personally released brown trout into the waters of Yellowstone National Park, but we have the ability to remove these invaders and restore the populations of the emblematic Yellowstone cutthroat trout. The legacy of Yellowstone rides on the back of this keystone species, and we must help them reclaim the frontier that was stolen by the outlaw brown trout.

For other Cal Poly Humboldt student posts, please see:

About the author:

Hello! My name is Madison Richardson, and I am currently a Marine Fisheries Biology student at Cal Poly Humboldt. I am an avid outdoorswoman and fisherwoman with my parents to thank for these qualities. My love for fish began as a small child who spent countless summers camping and fishing in many of the lakes in the Sierra Nevada mountains. I decided during these years that I wanted to pursue a career in fisheries. After writing an essay about the impacts of overfishing in the ocean in high school, I became interested in the management aspect of marine fisheries. In my future, I hope to become a fisheries biometrician and help bring about lasting positive change in marine fisheries management.


Al-Chokhachy, R., and A. J. Sepulveda. 2019. Impacts of nonnative brown trout on Yellowstone cutthroat trout in a tributary stream. North American Journal of Fisheries Management 39: 17-28.

Bigelow, P. E., T. M. Koel, D. Mahony, B. Ertel, B. Rowdon, and S. T. Olliff. 2003. Protection of native Yellowstone cutthroat trout in Yellowstone Lake, Yellowstone National Park, Wyoming. BiblioGov Project.

Budy, P., and J. W. Gaeta. 2017. Brown Trout as an Invader: A Synthesis of Problems and Perspectives in North America. Utah State University, Department of Watershed Sciences and the Ecology Center, Logan, Utah, USA.

Chrestenson, J. K. K. A. N. 2018. Montana FWP Issues Kill Order for Brown Trout on Stretch of Kootenai River.

Clayton, P. 2021. Where the mountains meet the plains, the Yellowstone Cutthroat splashes the east slop waterways with red and gold. Fish Eye Guy Photography.

Gresswell, R. E. 2009. Yellowstone Cutthroat Trout (Oncorhynchus clarkii bouvieri): a technical conservation assessment. USDA Forest Service, Rocky Mountain Region.

Juracek, J. 2011. Fly fishers head to Yellowstone’s Madison River for an annual visit of brown trout each fall. The Salt Lake Tribune.

NPS (National Park Service). 2009. Yellowstone cutthroat trout: Conserving a heritage population in Yellowstone Lake.

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