Fly fishing

Biologists plan to poison bass that threaten Grand Canyon chub

LEES FERRY — The National Park Service will poison a side channel of the Colorado River below Glen Canyon Dam to remove fish that threaten native species, the agency said.

Meanwhile, biologists warn, rising temperatures and falling oxygen levels in the water the dam releases into the Lees Ferry stretch of the river are stressing popular trout fishing there. .

Non-native smallmouth bass have been known to pass through the dam’s hydroelectric turbines for several years to reach the Lees Ferry area, but their successful breeding at this stretch was only documented this year. If this continues, agency officials fear, bass could settle far downstream and eat humpback chub, which are protected as an endangered species.

“Threats to native fish are increasing due to warmer water temperatures passing through the dam and the associated increase in river temperatures below the dam,” according to a statement released by the National Recreation Area of Glen Canyon, which includes the segment of the river. Warmer water apparently helped bass breed below the dam, “highlighting the urgency of this emerging problem”.

Paul McNabb holds a smallmouth bass, June 9, 2022, on Lake Powell near Page, Arizona.

On July 1, the Park Service found young bass swimming in a swamp connected to the river about 3 miles below the dam and 12 miles upstream from where anglers and rafters launch boats at Lees Ferry . It’s the same swamp where biologists have tracked another Lake Powell invader, the green sunfish, in recent years. The agency said it will treat the quagmire with the fish-killing rotenone on Saturday and Sunday. A second treatment may be required within two months if more invasive fish are found to have hatched or hidden in the dense vegetation of the area.

While rotenone is a plant-derived chemical commonly used by fish handlers, and the Park Service has said it will carefully protect the environment and human health by isolating it in the swamp, at least one Native American tribe with cultural ties to the river and the Grand Canyon objected. The Zuni Pueblo of New Mexico consider the river and the canyon to be sacred. Asked about a response to the fish kill plan, the Zuni provided the Arizona Republic with a Sept. 8 letter that Zuni Governor Val Panteah Sr. sent to the acting superintendent of Glen Canyon.

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“The Zuni objection is based on our traditional cultural values ​​and the enduring Zuni kinship relationship with all non-human life forms (plants, animals, insects, native and non-native) who have the right to life, liberty and procreation within their natural environments,” Panteah wrote.

After finding the young bass, the Park Service installed a fabric barrier to prevent them from leaving the quagmire and entering the river. The agency said it would put a water-purifying chemical, potassium permanganate, there and in the river just upstream of the quagmire to neutralize the rotenone. The quagmire will be closed during treatment, but the river – popular with anglers and kayakers – will remain open.

The stretch of river from the dam to Lees Ferry is at the center of government efforts to protect the humpback chub, which only last year was downlisted from endangered species. Beyond the bass and other introduced sport fish that swim just above the dam and might cross, the brown trout that the Park Service itself stocked for anglers in the river during the 20th century is a potential threat. Because of this, anglers can now claim a bounty for browns they kill in the river.

But deteriorating river conditions are now threatening rainbow trout fishing, which is considered less dangerous to native fish and supports several fly fishing guide services. The United States Bureau of Reclamation, which operates the dam, said this month that the same drought conditions that plunged Lake Powell’s water levels into crisis are now leaving Lees Ferry starved of oxygen. Warmer water has less dissolved oxygen, and the elevation of the reservoir’s sinking surface causes warmer flows through the dam’s tunnels.

Like many problems with Colorado’s dwindling water supply, this one is accelerating.

“Reclamation’s water quality forecast suggested it was possible to achieve low dissolved oxygen levels below the dam this year, but we did not expect this to happen until the start of the fall,” Reclamation fish biologist Clarence Fullard said in a statement.

Low oxygen levels can stress and kill trout or force them to move downstream where rapids add oxygen to flowing water. For now trout remains evident in abundance at Lees Ferry. They caught Page Police Officer Chris Seamster last week, where he saw them but couldn’t coax a bite out of his lure.

“It might inspire me to learn how to fly fish,” Seamster said as he left his post near Paria Beach, below the Lees Ferry boat launch. “A lot of people were jumping. I saw a whole bunch of little ones following the rooster tail.

Fishing remains good, although downstream water temperatures that should be around 50 degrees in summer are more like around 70, said Wendy Gunn, who owns and operates Lees Ferry Anglers. The midges feed the trout, even if these trout are stressed.

Wendy Gunn talks trout fishing, Sept. 9, 2022, at Lees Ferry Anglers, Marble Canyon, Arizona.

“The food base is still good,” Gunn said, “so we’re still seeing healthy fish, but we’re starting to see struggling fish and we’re seeing dead fish.”

In the short term, Gunn said, Lake Powell’s seasonal turnover, when cooler layers mix with warmer layers, should bring some temperature relief to the river by next month. Beyond that, there is a less reliable remedy: snow. Without a big snowpack in the Rockies, she said, the reservoir’s continued decline could warm the river further next summer, worsening oxygen depletion.

Brandon Loomis covers environmental and climate issues for The Arizona Republic and Contact him at [email protected] or follow him on Twitter @brandonloomis.

Environmental coverage on and in the Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic’s environmental reporting team at and @azcenvironment on Facebook, Twitter and Instagram.

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