Biologists’ fears were confirmed on the lower Colorado River

DENVER — For National Park Service fisheries biologist Jeff Arnold, it was a moment he had dreaded. Barelegged in sandals, he was dragging a net in a shallow backwater of the lower Colorado River last week when he spotted three juvenile fish that didn’t belong there. “Call me when you get this!” he texted a colleague and snapped photos.

Minutes later, the valet confirmed their worst fears: smallmouth bass had indeed been found and were likely breeding in the Colorado River below Glen Canyon Dam.

They may be a popular sport fish, but smallmouth bass feed on humpback chub, an ancient, endangered fish native to the river that biologists like Arnold have worked hard to recover. The predators wreaked havoc in the upper river but were kept at bay in Lake Powell, where Glen Canyon Dam served as a barrier for years – until now. The recent sharp decline in the reservoir allows these introduced fish to move past the dam and closer to where the largest groups of chub remain further downstream in the Grand Canyon.


There, Brian Healy has been working with the humpback chub for more than a decade and founded the Native Fish Ecology and Conservation Program.

“It’s quite devastating to see all the hard work and effort you put into removing other invasive species and relocating populations to protect the fish, and to see how all of those efforts were frustrated very quickly ‘ Healy said.

As the reservoir’s level drops, non-native fish that live in warm surface waters in Lake Powell approach the dam and its penstocks — submerged steel pipes that carry water to turbines, where it generates hydroelectric power and is released out the other side.

If bass and other predatory fish continue to be sucked into the penstocks, survive, and breed below the dam, they have an open lane to attack chub and other natives, potentially undoing years of restoration work and turning the Grand Canyon’s aquatic ecosystem upside down – the only stretch of river still dominated by native species.


Threatened with extinction decades ago, the chub has returned in modest numbers thanks to fish biologists and other scientists and engineers. Authorities spend millions of dollars annually to keep invaders at bay up the river.

Under the Endangered Species Act, government agencies are required to act in a manner that does not “endanger” the “continued survival” of listed animals. This includes the infrastructure.

Even before the discovery of smallmouth bass spawning below the dam, agencies had been preparing for this moment. The US Bureau of Reclamation recently commissioned a research team from Utah State University to do this Map the non-native fish in Lake Powell and try to determine which ones might pass through the dam first.

A task force was quickly assembled earlier this year to address the urgency that low water poses to native fish. Federal, state and tribal leaders are expected to release a draft plan in August that will provide solutions for policymakers intent on delaying, slowing and responding to the threat of smallmouth bass and other predators below the dam.


There are a variety of solutions, but many require significant infrastructure changes.

Meanwhile, the National Park Service, US Geological Survey, and Arizona Fish and Game are making quick efforts to contain the problem. During an emergency meeting, they decided to step up their surveillance efforts in other shallow areas and to shut off all backwater where the smallmouth bass were found, preventing them from swimming into the river.

“Unfortunately, the only block nets we have are fairly large mesh, so it won’t stop these smaller fish from getting through, but it will stop the adults from going back out,” Arnold said, noting that it’s the best they can do can do with available resources.

Experts say the best solution would be to leave more water in Lake Powell to ensure cool water can be released through the dam, although this is difficult in a river under so much stress.

Last month, the Department of the Interior told states that depend on the water of the Colorado River—that is, the entire Southwestern United States—that they must find a way to receive one-fifth to one-fourth of the river’s supply in 2023, or have to face federal intervention. It’s unclear where these preserved supplies will be stored, but Healy hopes Lake Powell will be considered.


“If we’re going to protect some of the values ​​that Grand Canyon National Park was established to protect, we really need to think about how water is stored,” Healy said. “This issue needs to be brought to the table.”


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https://www.local10.com/tech/2022/07/06/biologists-fears-confirmed-on-the-lower-colorado-river/ Biologists’ fears were confirmed on the lower Colorado River

Sarah Y. Kim

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