Biologists try to save ancient fish as Colorado River fades


PAGE, Ariz. (AP) — Barrett Friesen steers a motorboat toward the shore of Lake Powell, with Glen Canyon Dam overhead. Pale “bathtub rings” line the rock face of the canyon, starkly illustrating the drop in water levels in America’s second-largest reservoir amid rising demand and a years-long drought.

The Utah State University graduate student and his colleagues are on a mission to save the humpback chub, an ancient fish attacked by non-native predators in the Colorado River. The reservoir’s decline could soon make matters worse, allowing these introduced fish to cross the dam to where the largest groups of chub are found, farther downstream in the Grand Canyon.

On the brink of extinction decades ago, the chub has returned in modest numbers thanks to fish biologists and other scientists and engineers. But an emerging threat becomes evident in early June as Friesen hauls in minnow traps and gillnets filled with carp, gizzard shad, green sunfish and, worryingly, three smallmouth bass.

“Public enemy number one,” he says as lab technician Justin Furby weighs one on a portable scale.

Smallmouth bass feast on humpback chub in the upper part of the river. The agencies there spend millions of dollars each year to control these intruders. Native fish are safer below the Glen Canyon Dam because it blocks the way to Lower Colorado and the Grand Canyon, about 200 miles (322 kilometers) downstream – but that may not be true for long.

Lake Powell bass generally prefer warmer waters in shallow areas and on the surface. As reservoir levels drop, they draw closer to the dam and its penstocks – submerged steel tubes that carry water to turbines, where it generates hydroelectric power and is released from the reservoir. ‘other side.

If large numbers of bass and other predatory fish are sucked into the penstocks, survive and breed below the dam, they will have an open avenue to attack chub and other natives, potentially undoing years of restoration work. and disrupt the Grand Canyon’s aquatic ecosystem.

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

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

Although biologically a minnow, the humpback chub can reach 20 inches (51 centimeters) and 2.5 pounds (1.1 kilograms). Silver-sided and white-bellied, with a greenish streak on its back and a distinctive hump behind its head, it prefers calm rough waters where it feeds on insects.

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

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

Last year, the United States Fish and Wildlife Service relaxed its designation to threatened — closer to extinction, but still highly vulnerable. Some environmental groups disagree, calling the move premature because the falling river increases the danger of predation.

As early as this fall, significant numbers of bass and other non-native species could escape 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 operate in a way that does not “jeopardize the continued existence” of listed animals. This includes infrastructure.

The United States Bureau of Reclamation, a branch of the Department of the Interior that operates the dam, is funding Friesen’s fieldwork as part of Utah State’s Fish Ecology Lab. The team catches fish, records length and weight, and examines stomachs to see what the fish are eating. Their findings about non-natives near the dam will help federal, state, and tribal policymakers refine their strategy. A technical team advising policymakers is expected to release a draft plan with solutions in August.

One measure being considered if non-native predators cross the dam is to deploy crews to catch as many as possible. They already do that with brown trout upstream, Yackulic said. But it’s expensive and not always successful. Native American tribes such as the Pueblo of Zuni consider the Glen Canyon area sacred and oppose the killing of fish there, any fish.

“The Zuni don’t necessarily distinguish between native and non-native life forms,” ​​said Arden Kucate, a tribal councilor. “Strong stewardship is absolutely necessary, a philosophy that recognizes and treats all non-human life forms as sentient beings.”

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

Or cold water could also be released from reaction tubes at the bottom of the dam to disrupt smallmouth bass spawning downstream, a move that has been successful in other rivers.

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

This decision, however, would sacrifice hydropower generation. To solve this problem, turbines could be installed at the reaction tubes, but this would require congressional approval. These steps also depend on having enough fresh water in the river. Lake Powell levels had been relatively stable for about 15 years, but since 2020 they have dropped dramatically.

“Where will the water come from to support these necessary flows?” said Anne Castle, senior fellow at the University of Colorado School of Law and former U.S. Assistant Secretary of the Interior for Water and Science.

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 supplies, both voluntarily and forcibly.

“We’re going to rely on these extraordinary relationships and the history we have of cooperation on the river to find solutions,” Pullan said.

In the worst case, Lake Powell falls so far that water does not flow past the dam past a trickle, a condition known as a “deadpool”. That may be unlikely in the next few years, but planners should consider “a future in which Lake Powell ceases to exist,” said Taylor McKinnon, campaign manager for public lands at the Center for Biological Diversity, a group defense.

The prospect is real enough for the Home Office to discuss how to protect native fish if it happens, Pullan said.

The humpback chub wouldn’t be the only victim, McKinnon said. Deadpool would also reduce water supplies to communities in the South West.

“It’s a sign of our own self-destruction,” he said.


Flesher reported from Traverse City, Michigan.


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