Declining levels at #LakePowell increase risk to humpback chub downstream: As temperatures rise, so does risk of invasive fish — @AspenJournalism

The confluence of the Colorado and Little Colorado rivers in the Grand Canyon, shown here in a September 2020 aerial photo from Ecoflight, represents an area where the humpback chub has rebounded in the last decade. That progress is now threatened by declining water levels in Lake Powell, which could lead to non-native smallmouth bass becoming established in the canyon. CREDIT: JANE PARGITER/ECOFLIGHT

Click the link to read the article on the Aspen Journalism website (Heather Sackett):

As climate change continues to shrink the nation’s second-largest reservoir, water managers are scrambling to prevent the release of an invasive fish into the Grand Canyon.

Smallmouth bass, a voracious predator and popular game fish, have been introduced into reservoirs throughout the Colorado River basin, including Lake Powell. The looming problem now is that as lake levels drop to historically low levels, the invasive fish are likely to escape beyond Glen Canyon Dam, threatening endangered fish in the canyon, whose populations have rebounded in recent years.

Detailed underwater photo of Smallmouth Bass Micropterus dolomieu. By Engbretson Eric, U.S. Fish and Wildlife Service – http://www.public-domain-image.com/public-domain-images-pictures-free-stock-photos/fauna-animals-public-domain-images-pictures/fishes-public-domain-images-pictures/bass-fishes-pictures/detailed-underwater-photo-of-smallmouth-bass-fish-micropterus-dolomieu.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=24858275

Smallmouth bass are a warm-water-loving species, hanging out in the top part of the water column, which is warmed by the sun. Until recently, the intakes for turbines at Glen Canyon Dam had been lower in the water column, where colder temperatures kept the fish away. But as the lake level falls, the warmer water band containing the smallmouth bass is sinking closer to the intakes, making it more likely that they will pass through the dam to the river below.

Warmer water below the dam also means a more ideal environment for the bass, which thrive in temperatures above 61 degrees Fahrenheit (16 degrees Celsius).

“With the levels we are expecting to get to this coming year, water temperatures are going to be warmer than they’ve been in 52 years in the Grand Canyon,” said Charles Yackulic, a research statistician with the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center.

The research center has been modeling the likelihood that smallmouth bass will become established below the dam under different scenarios and providing that information to decision-makers and water managers.

Jack Schmidt, a Colorado River researcher at Utah State University and former director of the research center, co-wrote — along with Yackulic and others — a March 2021 paper that sounded the alarm that future warming is likely to disproportionately benefit nonnative fish species to the detriment of native species. The problem from which all others stem, including the changing fish communities, and the reason Powell is so low in the first place is the climate-change-driven supply-demand imbalance, Schmidt said.

Annual CO2 emissions from fossil fuels, by world region

“If we are going to continue to load the atmosphere with carbon such that the atmosphere warms and the runoff in the Colorado River keeps getting lower and if we are going to keep consuming water, … then you can only play this game of staving off the inevitable for so long before it’s game over,” he said.

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