GLEN CANYON NATIONAL RECREATION AREA, Utah, Sept. 9, 2022 (Gephardt Daily) — The National Park Service is preparing to remove invasive smallmouth bass and green sunfish from the Colorado River below the Glen Canyon Dam.
NPS officials say the predatory fish were recently discovered breeding in areas of Glen Canyon National Recreation Area where they had not previously been found in large numbers. The non-native fish are threatening the recovery of humpback chub, which is listed as threatened under the Endangered Species Act, according to an NPS news release.
The humpback chub improved from endangered to threatened in October 2021, in part due to the success of the species in the Colorado River through the Grand Canyon, NPS officials said. Because smallmouth bass are aggressive predators, failure to quickly control their population in the Colorado River above the Grand Canyon could likely lead to the demise of the humpback chub.
Removal efforts are scheduled to begin Sept. 17. NPS officials will use an Environmental Protection Agency-approved pesticide to kill the fish, the release states. A second treatment likely will follow within about two months to address any fish that survived or may have hatched since the first treatment, NPS officials said.
“The treatment will be carefully planned and conducted to minimize exposure to rotenone and protect the health and safety of humans, the environment, desirable fish species, and livestock,” the release states.
NPS officials will be conducting tests prior to the treatment to determine the minimum effective concentration of rotenone for use during the treatment, the release states.
Rotenone is a natural substance derived from plant roots and has been effective at eliminating localized populations of smallmouth bass, including in the Colorado River Basin, NPS officials said.
An impermeable fabric barrier will be installed at the mouth of the slough for the duration of the treatments to minimize the exchange of water with the river, the release states.
