National Park Service to Permanently Remove This Species of Fish From Major River System

by Emily Morgan

The National Park Service recently announced it will use a toxic natural compound to remove non-native smallmouth bass fish species from the Colorado River below the Glen Canyon Dam in Glen Canyon National Recreation Area. They will also remove and green sunfish from the same river system.

According to a release from Glen Canyon National Recreation Area, the park service recently discovered a large number of these non-native predatory fish. They were found to be breeding in areas where they have not previously been found. In addition, they have been reported to threaten the recovery of humpback chub. The humpback chub is currently listed as threatened under the Endangered Species Act.

Last fall, the humpback chub was downlisted from endangered to threatened. This was in part due to the success of the species in the Colorado River. According to the park service, since the smallmouth bass species is aggressive, the lack of controlling their breeding in the Colorado River above the Grand Canyon could harm humpback chub.

NPS to remove various fish species during two different treatments

On September 17, teams will release EPA-approved fish piscicide rotenone to counteract this issue. The initial round is planned between September 17 and 18. In addition, there will also be a potential second treatment within two months.

The area surrounding the backwater slough, the slough itself, and a short distance up and downstream will remain closed. However, officials will not close the entire river.

In addition, officials will be careful to minimize exposure to rotenone and protect the health of humans. They will also do everything to protect the environment, other fish species, and surrounding livestock.

This past spring, Lake Powell’s water dropped to unprecedented levels. Now, that phenomenon is having adverse effects on the native fish populations below Glen Canyon Dam.

Smallmouth bass and green sunfish survive in the warmer levels of the lake’s waters closer to the surface. As that warmer water reaches the dam’s water intakes, aggressive non-native fish have a higher chance of passing through.

As a result, this increases the threats to the native fish in the Grand Canyon and Glen Canyon’s rainbow trout fishery.

Now, threats to the native fish are rising due to the warmer temperatures of water passing through the dam. Moreso, increased river temperatures below the dam are increasing breeding rates for non-native fish, and more native fish will be preyed upon.

In July, officials found juvenile smallmouth bass in the Colorado River below Glen Canyon Dam. This discovery highlighted the importance of this current problem. Before the planned kill, officials will also run tests to determine the minimum effective concentration of rotenone for use during the treatment as to not harm any other animals or humans.