Biologists’ fears confirmed on lower Colorado River

DENVER (AP) — For National Park Service fisheries biologist Jeff Arnold, it was a moment he dreaded. Bare-legged in sandals, he was pulling a net into a shallow backwater of the lower Colorado River last week when he spotted three young fish that didn’t belong there. “Call me when you hear this!” he messaged a colleague and took pictures.

Minutes later, the park service confirmed their worst fears: Smallmouth bass had indeed been found and likely reproduced in the Colorado River below Glen Canyon Dam.

They may be a beloved sport fish, but smallmouth bass feast 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 reaches of the river, but were stopped in Lake Powell, where the Glen Canyon Dam has served as a barrier for years — until now. The recent sharp drop 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 over a decade and founded the Native Fish Ecology and Conservation Program.

“It’s pretty devastating to see all the hard work and effort you’ve put into removing other invasive species and moving populations to protect the fish and seeing all that effort wiped out very quickly. said Helen.

As reservoir levels drop, non-native fish living in warm surface waters in Lake Powell move closer to the dam and its weirs — submerged steel pipes that transport water to turbines, where it generates hydroelectric power and is released at the other end.

If bass and other predatory fish continue to be sucked into the veins, survive and reproduce under the dam, they will have an open avenue to attack chub and other natives, potentially unraveling years of restoration work and rebuilding the Grand Canyon’s aquatic ecosystem. is turned upside down – the only part of the river still dominated by native species.

Decades ago on the brink of extinction, the chub has made a comeback in modest numbers thanks to fish biologists and other scientists and engineers. Agencies spend millions of dollars annually to control invaders in the upper part of the river.

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

Even before the discovery of smallmouth bass spawning beneath the dam, agencies had braced for this moment. The U.S. Bureau of Reclamation recently engaged a team of researchers from Utah State University to: map the exotic fish in Lake Powell and try to determine which one can go through the dam first.

A task force quickly met earlier this year to address the urgency of the low tide for native fish. Federal, state and tribal leaders are expected to publish a draft plan in August that includes solutions for policymakers who plan to delay, delay and respond to the threat from smallmouth bass and other predators beneath the dam.

There are several solutions, but many of them require major infrastructure changes.

Meanwhile, the National Park Service, US Geological Survey and Arizona Game and Fish Department are moving quickly to try and contain the problem. At an emergency meeting, they decided to increase their monitoring efforts in other shallow areas and close off the entire backwater where the smallmouth bass was found, preventing them from swimming into the river.

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

Experts say leaving more water in Lake Powell would be the best solution to ensure cool water can be drained through the dam, although it’s difficult to do in a river that’s under so much stress.

Last month, the Department of the Interior notified the seven western states that depend on the water from the Colorado River that they must figure out a way to save up to 4 million acre feet of water by 2023 — more than the share of Arizona and Nevada together – or face federal intervention. It’s unclear where that conserved stock would be stored, but Healy says he hopes Lake Powell is being considered.

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

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