Predators are threatening ancient fish, including the "public enemy number one".

Barrett Friesen leads a motorboat towards Lake Powell.

02 July 2022 Saturday 07:28
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Predators are threatening ancient fish, including the "public enemy number one".

Barrett Friesen leads a motorboat towards Lake Powell. The Glen Canyon Dam is visible overhead. The canyon's rock face is lined with pale "bathtub rings", which starkly illustrate how water levels have plummeted in the second-largest U.S. storage, amid rising demand and a multiyear drought.

A graduate student at Utah State University and his colleagues are on a mission: to save the Colorado River's humpback Chub, an endangered fish that is being threatened by non-native predators. These introduced fish may be able to pass the dam and reach the Grand Canyon, where there are still large numbers of chub.

The chub was on the verge of extinction many decades ago. However, it has been able to repopulate in small numbers due to the efforts of fish biologists, other scientists and engineers. Friesen catches minnow traps, gillnets, and green sunfish packed with carp and gizzardshad.

He calls Justin Furby, a lab technician, "Public enemy number one" as he weighs one on a scale.

Smallmouth bass love humpbacks chub, which is found in the upper river section. To keep these intruders under control, agencies spend millions of dollars annually there. Although the Glen Canyon Dam blocks the route to the Lower Colorado, and Grand Canyon, which is about 200 miles downstream, the native fish have been more secure there than elsewhere. But that could change.

Lake Powell bass prefer warm waters at the surface and in shallower areas. As the reservoir level drops, the bass are getting closer to the dam.

If large numbers are caught in the penstocks by predator fish, such as bass, and they survive and reproduce below it, they will have an open channel to attack natives and chub, which could lead to years of restoration and upkeep of the Grand Canyon's aquatic ecosystem.

Brian Healy (grand Canyon National Park fisheries biologist), said that this stretch of river is where native fish still dominate. It is a very special place and we want it to stay that way.

The 1963 completion of the dam was the primary reason that the chub almost died in the river they had lived for many millions of years. Concrete barriers disrupted water flow, temperature and sediments at the fishspawning sites. Although the chub is resilient, it hasn't evolved to resist predatory fish.

The humpback, although biologically a minnow is a humpback chub. It can grow to 20 inches in length and 2.5 pounds. It is silver-sideded and white-bellied with a greenish streak on the back and a distinct lump behind its head. It prefers calm eddy water to feed on insects.

The only predator of the Colorado pikeminnow was another native species. Until the introduction of trout in the early 20th Century to make it a sport fishery, the pikeminnow was the only predator. The 1990s saw the arrival of smallmouth bass, which is even more aggressive.

Since 1967's listing of the chub as endangered, the chub has seen a lot of progress. There are approximately 12,000 chubs in the Grand Canyon's Little Colorado River. This river is a tributary to the Colorado. Scientists believe that thousands more live in the river's downstream section.

The U.S. The U.S. Fish and Wildlife Service loosening its designation to endangered last year -- not a step away form extinction but still very vulnerable. Some environmental groups disagree with the decision, claiming that the river's plunge increases predation risk.

Charles Yackulic is a statistician at the U.S. Geological Survey who has created computer models to assess the threat. He said that significant numbers of non-native bass could escape the dam as early as this fall.

The Endangered Species Law requires government agencies to ensure that they do not "jeopardize" the continued existence of endangered species. This includes infrastructure.

Friesen's fieldwork is funded by the U.S. Bureau of Reclamation. This branch of the Department of the Interior operates the dam. Friesen's team captures fish and records their length, weight, and examinations their stomachs to determine what the fish are eating. The team's findings on non-natives living near the dam will assist federal, state, and tribal policymakers in fine-tuning their strategies. In August, a technical team that advises policymakers is expected to publish a draft plan with solutions.

If non-native predators are able to get past the dam, one option is to deploy crews to capture as many as possible. Yackulic stated that they already do this with brown trout upstream. It's costly and sometimes not successful. Native American tribes like the Pueblo of Zuni regard Glen Canyon as sacred and are against killing fish there.

Arden Kucate, a tribal councilman, stated that "Zuni don't necessarily make distinctions among native and non-native life forms." Strong stewardship is essential, as well as a philosophy that treats all nonhuman life forms with respect and recognizes them as sentient beings.

You can also choose to penned areas downstream of the dam where chub congregate, or install structures like "bubble curtains", which will keep non-natives from Lake Powell from the penstocks.

To disrupt smallmouth bass spawning downstream of the dam, cold water could be released from deep within the dam's jet tubes. This move has been successful in other rivers.

Clarence Fullard, a Bureau of Reclamation fish biologist, stated that the dam can be used essentially as an instrument.

However, this would mean hydropower generation would be sacrificed. The possibility of installing turbines at the jet tubes could address this problem, but it would need congressional approval. This will also require that there is enough cool water in river. The levels at Lake Powell have dropped dramatically since 2020. They were relatively stable for 15 years.

"Where will the water come from to sustain these flows?" Anne Castle, a senior fellow at the University of Colorado Law School and an ex-assistant U.S. attorney, said: Interior secretary for science and water.

Wayne Pullan, who is responsible for the Upper Colorado Basin at the Bureau of Reclamation declined to speculate. However, in recent years, Mexico, states, tribes, and Mexico have made cuts to their supply, both forced and voluntary.

Pullan stated, "We're going on to rely upon those extraordinary relationships as well as the history of cooperation on this river to find solutions."

Lake Powell could fall so far that the water can't flow beyond the dam, which is known as "deadpool". Although it may not be possible in the near future, planners should look ahead to "a future where Lake Powell ceases being alive," Taylor McKinnon said. He is a senior public lands campaigner at the Center for Biological Diversity.

Pullan stated that this possibility is so real that the Department of Interior is currently discussing how to protect native fish.

McKinnon stated that the Humpback Chub would not be the only ones to suffer. Deadpool would also cut off water supply to Southwest communities.

He said, "That's a sign of our own self destruction."



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