September 28, 2023 | NEWS | By Erin Mullins and Phoebe Gordon

Colorado College’s Block One animal ecology course was taught by professor Brian Linkhart, who has studied fish populations in the Yampa and Little Snake Rivers for 20 years. This year, the class discovered a smallmouth bass for the first time in the Little Snake River, which could potentially have negative consequences for the river’s future.

The Yampa River is an important tributary of the Colorado River, which supplies water to five states in the Southwestern United States. What sets the Yampa apart from the rest of the river system is its free-flowing watershed.

Because of the Yampa’s importance, Linkhart has taken it upon himself to sample the young fish communities of both the Yampa the Little Snake, one of the Yampa’s largest tributaries.

“My own K-12 education did nothing to excite me about biology and science. . . It was all through personal experiences,” Linkhart said.

This project, executed by Linkhart’s animal ecology class, has been running for 20 years, has generated the only known gathered fish data from the Little Snake River, and has given students hands-on experience in the field. The Little Snake has historically been a safe haven for native fish due to its distance from reservoirs, which are hotspots for the introduction of sport fish that can occasionally be released into adjacent rivers.

This year, the 20th year of the Little Snake sampling project, yielded a surprise visitor. For the first time, a smallmouth bass was discovered in the Little Snake. While more data is needed to conclude what is happening with bass populations in the river, it is possible that this occurrence could have serious consequences for native species.

John Hawkins, a senior research associate at the Larval Fish Lab in the Department of Fish, Wildlife, and Conservation Biology at Colorado State University, joined the class as a resident biologist familiar with the Yampa and Little Snake.

According to Jones, Hawkins, and Linkhart, due to the size of the bass, it most likely spawned in the Little Snake rather than spawning in the Yampa River and swimming miles upstream.

Because the Yampa has no flow-restrictive dams and only one reservoir, Elk Head, there is less potential for invasion by non-native fishes compared to the rest of the Colorado River Basin. The natural fluctuations in flow that the rivers experience cause them to be very cloudy, preventing non-native fish from taking hold of the population.

Non-native fish generally have lower visibility in the cloudy water, which keeps them from preying on natives and establishing a strong foothold in the system. The native fish, which evolved in the cloudy water, are better equipped to survive there.

A small, dammed tributary of the river, which forms the Elk Head reservoir, was stocked with smallmouth bass. The bass are voracious predators of native fish and compete with them for various resources.

According to Tildon Jones, associate director of the Upper Colorado River Endangered Fish Recovery Program, “The bass have escaped or leaked out of those reservoirs and have established into river populations near those reservoirs and even downstream quiet ways.”

Damming, redirecting water, and the introduction of new species have changed and continue to change much of the Colorado River Basin.

Additionally, the river system has a long history of intentional non-native fish introductions for sport fishing, with some of the most familiar being rainbow trout, brown trout, and northern pike. The introduction of these sport fishes brings people closer to the river but can mean serious consequences for the native ecosystem. Many of these introductions start in reservoirs, which can be especially popular fishing spots.

In a 1992 accidental release, the fish made their way into the Yampa. Because bass can impact native fish both directly by eating them and indirectly by taking resources, their effect on native populations can be extreme. Jones described the bass as “highly predacious.”

Efforts, such as the Colorado River Recovery Project, have been in place to remove the bass and other non-natives for many years by retrofitting dams, changing the surrounding habitats, raising and stocking native fish, and outreach.

Both Jones and Hawkins described the feeling of finding the smallmouth bass as “disappointing,” but felt that the discovery provoked more questions than answers. Jones said that he is “not sure what it means . . . I don’t know if it is cause for alarm. I think we need to take a deeper look into it.” Hawkins said, “it is a data point.”

For people who have studied the river, the bass also has an emotional impact. While there are many serious scientific reasons to keep the Little Snake bass-free, Hawkins argues for a more ethical approach saying: “Those fish have intrinsic value. That means they have rights within [themselves].”

Hawkins goes on to say, “These fish are the only ones in the world that are native to this place … as biologists, we often learn about them and understand them and then we appreciate them, and we don’t always do a good job of sharing that knowledge.”

Although Hawkins and Jones are both biologists, they understand that the Yampa River serves more purposes than its role in the ecosystem. Bass were introduced into the Elk Head reservoir for sport fishing. That inherently brings revenue into the area and involves the long-divisive problem of water rights. Hawkins said, “It deserves more information before you go too far… I have hope for the Little Snake…but people need water.”

There is no clear-cut solution to the bass problem. Conservation efforts continue: although, so do the bass. Efforts such as those in Linkhart’s class are vital to understanding the scope of the problem so informed decisions can be made to better the ecosystem and the surrounding community. 

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