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Wednesday, June 29, 2022

Biologists try to save ancient fish as the Colorado River fades

Page, Ariz. Barrett Friesen drives a motorboat along the upper part of the Glen Canyon Dam towards the shores of Lake Powell. Yellow “bathtub rings” line the canyon’s rocky face, clearly showing how water levels in the second-largest US reservoir have plummeted amid rising demand and a multi-year drought.

Utah State University graduate students and colleagues are on a mission to save the humpback chub, an ancient fish under attack from non-native predators in the Colorado River. Reservoir degradation could soon make things worse, allowing these introduced fish to move beyond the dam where the largest groups of chub live, further into the Grand Canyon.

On the brink of extinction decades ago, the chub is back in modest numbers thanks to fish biologists and other scientists and engineers. But an emerging threat becomes apparent in early June as Fryson catch minnow traps and gillnets packed with carp, gizzard shad, green sunfish and, ominously, three smallmouth bass.

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

Smallmouth bass feast on humpback chub in the upper reaches of the river. Agencies spend millions of dollars there annually to keep those intruders under control. The native fish has been protected beneath the Glen Canyon Dam because it blocks the passage of the Lower Colorado and Grand Canyon, about 200 miles (322 kilometers) downstream – but this may not be true for long.

Bass up in Lake Powell generally prefer shallow areas and warm water at the surface. As the reservoir level drops, they are drawing closer to the dam and its penstocks – submerged steel tubes that carry water to turbines, where it generates hydroelectricity and is released to the other side.

If large numbers of bass and other predatory fish are sucked into the penstocks, surviving and breeding under the dam, they will have an open alley to attack chub and other natives, potentially leading to restoration. To highlight years of work and uplift the Grand Canyon aquatic ecosystem.

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

The completion of the dam in 1963 was a primary reason why the Chubs almost died in the river they had inhabited for millions of years. The concrete barrier impeded water flow, temperature and sediment where the fish were born. The chew is resilient, but the predator has not evolved to withstand the sudden introduction of game fish.

Although biologically a small, humpback chew can reach 20 inches (51 cm) and 2.5 pounds (1.1 kg). Silver-sided and white-bellied, with a green streak on its back and a distinctive lump on the back of the head, it prefers calm eddy waters where it feeds on insects.

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

The chub has gained land since being listed as endangered in 1967, along with about 12,000 in the Little Colorado River of the Grand Canyon, a tributary of Colorado. Scientists estimate that thousands more live downstream in the main river.

The US Fish and Wildlife Service last year put its designation in danger – no longer a step away from extinction, but highly vulnerable nonetheless. Some environmental groups disagree, calling the move a premature river dip, adding to the predation threat.

Also this fall, significant numbers of bass and other non-native people could exit through the dam, said Charles Yakulik, 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 ways that “would not endanger the continued existence” of listed animals. Including infrastructure.

The US Bureau of Reclamation, a branch of the Department of the Interior that operates the dam, is funding Frison’s fieldwork under Utah State’s Fish Ecology Lab. The team catches the fish, notes the length and weight, and examines the abdomen to see what the fish are eating. Their findings about non-natives near the dam will help federal, state and tribal policymakers fine-tune their strategy. A technical team advising policymakers is expected to release a draft resolution plan in August.

One solution under consideration is to deploy crews to catch as many as possible if non-native predators do get through the dam. They already do this with brown trout upstream, Yakulik said. But it is expensive and not always successful. Native American tribes such as the Pueblo of the Zuni consider the Glen Canyon area sacred and oppose killing any fish there.

Aboriginal councilor Arden Cucate said, “The Juni do not necessarily distinguish between native and non-native life forms.” “There is a great need for strong leadership, a philosophy that recognizes and treats all nonhuman life forms as sentient beings.”

Other options include closing off areas below the dam where chews congregate or installing structures such as “bubble curtains” to keep non-dwellers in Lake Powell away from penstocks.

Or cold water can also be released from jet tubes deep in the dam to disrupt smallmouth bass downstream, a move that has been successful in other rivers.

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

However, this move would abandon hydropower generation. To address this, turbines could be mounted on jet tubes – but that would require congressional approval. These steps also depend on the availability of sufficiently cold water in the river. The level of Lake Powell was relatively stable for about 15 years, but has fallen dramatically since 2020.

World Nation News Desk
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