PAGE, Ariz. — Barrett Friesen steers a motorboat towards 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 ranges have slumped within the second-largest US reservoir amid rising demand and a multi-year drought.
The Utah State College graduate pupil and colleagues are on a mission to save lots of the humpback chub, an historic fish below assault from nonnative predators within the Colorado River.
The US Bureau of Reclamation fundsFriesen’s fieldwork to assist federal, state and tribal policymakers fine-tune their technique..
The staff notes size and weight of fish and examines stomachs to see what they’re consuming. A draft plan containing options is anticipated to be launched in August.
The reservoir’s decline might quickly make issues worse, enabling these nonnative predators to get previous the dam to the place the largest teams of chub stay, farther downstream within the Grand Canyon.
Getting ready to extinction a long time in the past, the chub has come again in modest numbers because of fish biologists and different scientists and engineers. However an rising risk turns into evident in early June as Friesen hauls up minnow traps and gillnets filled with carp, gizzard shad, inexperienced sunfish and, ominously, three smallmouth bass.
Smallmouth bass feast on humpback chub within the river’s higher part. Companies spend tens of millions of {dollars} yearly to maintain these intruders in examine. The native fish have been safer under Glen Canyon Dam as a result of it blocks the trail to the Decrease Colorado and the Grand Canyon, some 200 miles downstream – however that might not be true for lengthy.
‘open lane to assault’
Bass up in Lake Powell typically desire hotter waters in shallow areas and on the floor. As reservoir ranges drop, they’re edging nearer to the dam and its penstocks — submerged metal tubes that carry water to generators, the place it generates hydroelectric energy and is launched on the opposite facet.
If giant numbers of bass and different predator fish are sucked into the penstocks, survive and reproduce under the dam, they’re going to have an open lane to assault chub and different natives, probably unraveling years of restoration work and upending the Grand Canyon aquatic ecosystem.
That stretch of river is the one place native fish nonetheless dominate the system, mentioned Brian Healy, fisheries biologist for Grand Canyon Nationwide Park.
“(It) may be very distinctive and we need to preserve it that manner,” he mentioned.
Dam ‘main cause’ for decline of chub 60 years in the past
The dam’s completion in 1963 was a main cause the chub almost died out within the river they’d inhabited for tens of millions of years. The concrete barrier disrupted water circulate, temperatures and sediments the place the fish spawned.
The chub is resilient however hasn’t advanced to resist sudden introduction of predatory sport fish.
Though biologically a minnow, the humpback chub can attain 20 inches and a pair of.5 kilos. Silver-sided and white-bellied, with a greenish streak on its again and a particular lump behind its head, it prefers calm eddy waters the place it feeds on bugs.
Its solely predator within the Colorado was one other native, the pikeminnow, till trout have been launched within the early twentieth century to create a sport fishery. Smallmouth bass, much more voracious, arrived within the Nineties.
The chub has gained floor since its itemizing as endangered in 1967, with about 12,000 within the Grand Canyon’s Little Colorado River, a tributary of the Colorado. Scientists estimate 1000’s extra inhabit the primary river farther downstream.
The US Fish and Wildlife Service final yr loosened its designation to threatened — not a step away from extinction, however nonetheless extremely weak.
Some environmental teams disagree, calling the transfer untimely because the river’s plunge heightens predation hazard.
As early as this fall, important numbers of bass and different nonnatives may slip out by way of the dam, mentioned Charles Yackulic, a US Geological Survey statistician who has developed laptop fashions of the risk.
Underneath the Endangered Species Act, authorities businesses are required to function in methods that won’t “jeopardize the continued existence” of listed animals. That features infrastructure.
One measure into consideration if nonnative predators get by way of the dam is deploying crews to catch as many as doable. They already do this with brown trout upstream, Yackulic mentioned.
Nevertheless it’s costly and never at all times profitable. Native American tribes such because the Pueblo of Zuni contemplate the Glen Canyon space sacred and oppose killing fish there, any fish.
“Zuni don’t essentially make distinctions between native and nonnative life kinds,” mentioned Arden Kucate, a tribal councilman. “Robust stewardship may be very a lot wanted, a philosophy that acknowledges and treats all nonhuman life kinds as sentient beings.”
Why consultants are making ready for a ‘future by which Lake Powell ceases to exist’
Ranges at Lake Powell had been comparatively steady for some 15 years, however since 2020, have fallen dramatically.
In a worst case situation Lake Powell falls to date that water does not circulate previous the dam past a trickle, a situation generally known as “deadpool.”
It could be unlikely within the subsequent few years, however planners must be waiting for “a future by which Lake Powell ceases to exist,” mentioned Taylor McKinnon, senior public lands campaigner with the Middle for Organic Range, an advocacy group.
The prospect is actual sufficient that the Division of Inside is discussing how you can defend native fish if that occurs, Pullan mentioned.
Humpback chub would not be the one victims, McKinnon mentioned. Deadpool additionally would slash Southwest communities’ water provides.
“That may be a sign of our personal self-destruction,” he mentioned.