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Biologists Try to Save Ancient Fish as Colorado River Fades

PAGE, Ariz. – Barrett Friesen steers a motorboat to the shore of Lake Powell, where Glen Canyon Dam rises. Pale “bathtub rings” line the canyon’s rocky wall, vividly illustrating how water levels in the second-largest US reservoir have dropped in the face of rising demand and a multi-year drought.

The Utah State University graduate student and colleagues are on a mission to save the humpback chub, an ancient fish under attack by non-native predators in the Colorado River. The decline of the reservoir could soon make matters worse, allowing these introduced fish to slip past the dam where the largest groups of chub lie further downstream in the Grand Canyon.

Threatened with extinction decades ago, the chub has returned in modest numbers thanks to fish biologists and other scientists and engineers. But an emerging threat becomes apparent in early June when Friesian pulls up minnow traps and gillnets filled with carp, gizzards, green sunfish and, ominously, three smallmouth bass.

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“Public enemy number one,” he says as lab tech Justin Furby weighs you on a hand scale.

Smallmouth bass feast on humpback chub in the upper section of the river. Authorities there spend millions of dollars annually to keep these invaders at bay. Native fish were safer below Glen Canyon Dam because it blocks the route to Lower Colorado and the Grand Canyon about 200 miles (322 kilometers) downstream — but that may not be for long.

Lake Powell bass generally prefer warmer waters in shallow areas and on the surface. As the reservoir level drops, they 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 large numbers of bass and other predatory fish are sucked into the penstocks, survive, and reproduce below the dam, they have an open lane to attack chub and other natives, potentially undoing years of restoration work and reviving the Grand Canyon’s aquatic ecosystem turns his head.

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This stretch of river is the only place where native fish still dominate the system, said Brian Healy, Grand Canyon National Park fisheries biologist. “(It) is very unique and we want it to stay that way,” he said.

The completion of the dam in 1963 was one of the main reasons the chub almost went extinct in the river where they lived for millions of years. The concrete barrier disrupted water flow, temperatures, and sediment where fish spawned. The chub is resilient but has not evolved to withstand a sudden introduction of predatory sport fish.

Although biologically a minnow, the humpback whale can reach 51 centimeters (20 in) and 1.1 kilograms (2.5 pounds). Silver-sided and white-bellied, with a greenish stripe down its back and a prominent lump behind its head, it prefers calm, swirling waters where it feeds on insects.

Its only predator in the Colorado was another Native American, the pikeminnow, until trout were introduced to create a sport fishery in the early 20th century. The even more voracious smallmouth bass entered the market in the 1990s.

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The chub has been gaining ground with about 12,000 in the Little Colorado River of the Grand Canyon, a tributary of the Colorado River, since it was listed as endangered in 1967. Scientists estimate that thousands more inhabit the main river further down the river.

The US Fish and Wildlife Service last year eased its classification as vulnerable — no longer a step away from extinction, but still critically endangered. Some environmental groups disagree, calling the move premature because the river’s fall increases the danger from predators.

As early as this fall, significant numbers of bass and other non-natives could slip through the dam, said Charles Yackulic, a US Geological Survey statistician who has developed computer models of the threat.

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.

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The US Bureau of Reclamation, a division of the Department of Interior that operates the dam, is funding Friesen’s field research as part of the State of Utah’s Fish Ecology Lab. The team catch fish, note length and weight, and examine stomachs to see what fish are eating. Her insights into non-natives near the dam will help federal, state, and tribal decision-makers refine their strategy. A technical team advising policymakers is expected to release a draft plan with solutions in August.

One action considered if non-native predators do get through the dam is to use crews to capture as many as possible. They’re already doing that with brown trout upstream, Yakulic said. But it is expensive and not always successful. Native American tribes like the Zuni pueblo consider the Glen Canyon area sacred and refuse to kill any fish there, any fish.

“Zuni doesn’t necessarily differentiate between native and non-native life forms,” ​​said Arden Kucate, a tribal councillor. “Strong leadership is urgently needed, a philosophy that recognizes and treats all non-human life forms as sentient beings.”

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Other options include cordoning off areas downstream of the dam where chub congregate, or installing structures such as “bubble curtains” to keep non-natives in Lake Powell away from the penstocks.

Or cold water could also be released from nozzles deep in the dam to disrupt spawning smallmouth bass, a move that has been successful in other rivers.

“We can essentially use the dam as a tool,” said Clarence Fullard, a fish biologist with the Bureau of Reclamation.

However, this move would sacrifice hydroelectric power generation. To counteract this, turbines could be installed on the jets — but that would require congressional approval. These steps also depend on whether there is enough cool water in the river. Levels at Lake Powell have been relatively stable for about 15 years, but have dropped dramatically since 2020.

“Where is the water going to come from to support the needed rivers?” said Anne Castle, senior fellow at the University of Colorado Law School and former US Assistant Secretary of the Interior for Water and Science.

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Wayne Pullan, who oversees the Upper Colorado Basin for the Bureau of Reclamation, declined to speculate, though in recent years states, tribes and Mexico have cut their supplies, both voluntarily and coerced.

“We will rely on these exceptional relationships and our history of working together down the river to find solutions,” Pullan said.

At worst, Lake Powell drops so far that the water no longer flows past the dam as a trickle, a condition known as “deadpool”. It may seem unlikely in the next few years, but planners should look to “a future in which Lake Powell ceases to exist,” said Taylor McKinnon, senior public lands campaigner at the Center for Biological Diversity, an advocacy group.

The prospect is real enough that the Home Office is discussing how to protect native fish in this case, Pullan said.

Humpback chubs would not be the only victims, McKinnon said. Deadpool would also restrict the water supply to South West communities.

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“This is a signal of our own self-destruction,” he said.

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Flesher reported from Traverse City, Michigan.

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https://www.local10.com/news/national/2022/06/14/biologists-try-to-save-ancient-fish-as-colorado-river-fades/ Biologists Try to Save Ancient Fish as Colorado River Fades

Sarah Y. Kim

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