Scientists’ fight to save ancient fish key to health of Colorado River

PAGE, Ariz. — Barrett Friesen steers a motorboat toward the shore of Lake Powell, with the Glen Canyon Dam towering overhead.

Pale “bathtub rings” line the canyon’s rocky face, starkly illustrating how water levels have slumped in the second-largest US reservoir amid 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 assault from nonnative predators in the Colorado River.

The US Bureau of Reclamation funds Friesen’s fieldwork to help federal, state and tribal policymakers fine-tune their strategy..

The team notes length and weight of fish and examines stomachs to see what they are eating. A draft plan containing solutions is expected to be released in August.

A Utah State University research team pulls in a gillnet net at Lake Powell on Tuesday, June 7, 2022.
Utah State University master's student Barrett Friesen steers a boat through Lake Powell on June 7, 2022.
Utah State University master's student Barrett Friesen records data about the nonnative fish he is researching for the Bureau of Reclamation on June 7, 2022.

The reservoir’s decline may soon make things worse, enabling these nonnative predators to get past the dam to where the biggest groups of chub remain, farther downstream in the Grand Canyon.

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

Smallmouth bass feast on humpback chub in the river’s upper section. Agencies spend millions of dollars annually to keep those intruders in check. The native fish have been safer below Glen Canyon Dam because it blocks the path to the Lower Colorado and the Grand Canyon, some 200 miles downstream – but that may not be true for long.

‘Open lane to attack’

Bass up in Lake Powell generally prefer warmer waters in shallow areas and at the surface. As reservoir levels drop, they are edging closer to the dam and its penstocks — submerged steel tubes that carry water to turbines, where it generates hydroelectric power and is released on the other side.

If large numbers of bass and other predator fish are sucked into the penstocks, survive and reproduce below the dam, they’ll have an open lane to attack chub and other natives, potentially unraveling years of restoration work and upending the Grand Canyon aquatic ecosystem.

Utah State University lab technician Justin Furby weighs a smallmouth bass June 7, 2022. Smallmouth bass feast on humpback chub in the river's upper section, where agencies spend millions of dollars annually to keep the intruders in check.
Utah State University master's student Barrett Friesen steers a boat near Glen Canyon Dam on Lake Powell on June 7, 2022. The dam's completion in 1963 was a primary reason the humpback chub nearly died out in the Colorado River they had inhabited for millions of years.

That stretch of river is the only place native fish still dominates the system, said Brian Healy, fisheries biologist for Grand Canyon National Park.

“(It) is very unique and we want to keep it that way,” he said.

Dam ‘primary reason’ for decline of chub 60 years ago

The dam’s completion in 1963 was a primary reason the chub nearly died out in the river they had inhabited for millions of years. The concrete barrier disrupted water flow, temperatures and sediments where the fish spawned.

The chub is resilient but hasn’t evolved to withstand sudden introduction of predatory sport fish.

Although biologically a minnow, the humpback chub can reach 20 inches and 2.5 pounds. Silver-sided and white-bellied, with a greenish streak on its back and a distinctive lump behind its head, it prefers calm eddy waters where it feeds on insects.

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