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Will a dam save the pallid sturgeon, or doom it?

On the Yellowstone River, farmers and conservationists clash over controversial infrastructure.

 

Seventy million years ago, in the latter Cretaceous, the land that we call Montana had the same climate as modern Louisiana. Where wolves stalk elk, Tyrannosaurus rex hunted duck-billed hadrosaurs. The Rocky Mountains had just begun to rise from the plains, draining the inland sea that submerged present-day Billings. Grizzly bears and bison were distant glimmers in evolution’s eye. 

But there were already pallid sturgeon.

Scaphirhynchus albus is among the West’s oldest and strangest denizens. True to their name, pallid sturgeon are colored a ghostly whitish-gray, from shovel-like snout to elongated tail. They grow up to five feet long, reach 85 pounds, and live nearly as long as humans. Their skeletons are made of cartilage; in place of scales, they are armored with tough scutes. Their toothless, extendable mouths slurp invertebrates from muddy riverbeds. And, like many fish, pallid sturgeon are gravely harmed by dams.

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Pallid sturgeon have survived in the Missouri for 70 million years, but now fewer than 125 fish remain in the river's Upper Basin.
North Dakoka Game and Fish Department.

Beginning in 1940, the Bureau of Reclamation and the Army Corps of Engineers strung a half-dozen mammoth dams along the Upper Missouri River, turning the waterway into a concatenation of reservoirs as it ran through the Dakotas and Montana. As High Country News has reported, the dams blocked spawning migrations, stifling sturgeon in the build-up of sand and gravel in which the fish deposit eggs and eliminated floodplains and side channels where juvenile pallids grow up. Although the river is stocked with hatchery sturgeon to prevent extirpation, fewer than 125 wild-born adult fish now roam the Missouri’s Upper Basin — the rapidly senescing survivors of an ancient population, perishing of old age, one by one by one.

Rejuvenating the pallid population, scientists say, will require opening access to the Yellowstone River, the tributary where up to a quarter of the Upper Basin’s sturgeon travel to spawn. While the Yellowstone is nominally the longest free-flowing river in the lower 48, migrating pallids find their passage blocked by Intake Diversion Dam, a chain of jagged boulders near the town of Glendive that raises water levels just enough to shunt flows into an irrigation canal. The diversion, authorized by Congress in 1904, provides water for some 200 family farms and 58,000 acres of sugar beets, barley and hay.

Today, the federal government insists that the best way to help this dwindling population is by replacing Intake with a new, fish-friendlier dam. Proponents say the proposed dam, a low concrete weir circumvented by an artificial side channel, would provide adequate passage for pallids to reach upriver spawning grounds. But the plan infuriates many conservationists, who insist that tearing the dam out altogether is the only sure-fire way to help sturgeon. “Many of the scientists who’ve been tasked with reviewing this project have rejected it as a decent use of funds,” says Steve Forrest, senior Rockies and Plains representative with Defenders of Wildlife. “The government wants to spend $57 million despite not having any certainty about whether it will provide tangible results.” 

The Upper Missouri Basin’s dams have inflicted their greatest damage upon sturgeon embryos — translucent, tadpole-shaped newborns fresh out of the egg. These tiny migrants float downriver for days after hatching, covering anywhere from 150 to 500 miles, as they gain the strength and anatomy to swim. By dividing the Missouri Basin into short segments, dams fatally interrupted this developmental drift. Now the helpless embryos spill into reservoirs before they’re strong enough to propel themselves, where they're devoured by predators or suffocate in the oxygen-poor depths.

Potential salvation lies in the Yellowstone. If pallids could migrate above Intake dam, adult fish could take advantage of 165 miles of new spawning habitat, and embryos would have more space to drift. But while Intake resembles a natural rapid more than it does a goliath dam, it flummoxes fish nonetheless: In 2015, just one sturgeon passed Intake via a natural side channel. Most sturgeon must spawn below the obstacle, 70 miles from the Yellowstone’s confluence with the Missouri. Their floating embryos hit the mainstem and die in Lake Sakakawea, the reservoir formed by Garrison Dam, before they can morph into fully-fledged larvae. 

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Intake Diversion may not look like a massive dam, but it's a significant obstacle to sturgeon passage.
U.S. Army Corps of Engineers and Bureau of Reclamation

How best to assist fish beyond Intake has long been a matter of dispute. In 2010, the Bureau of Reclamation and the U.S. Army Corps of Engineers authorized construction on a rock ramp that would have helped the fish swim over the obstruction. When that scheme was nixed, the agencies shifted their support to the new dam and its fish passage structure, a winding, 2-mile-long artificial bypass channel. Unlike the current Intake structure, a concrete dam wouldn’t require the annual placement of new boulders; meanwhile, the channel would recreate the slow flows and habitat that sturgeon rely on in the wild, helping the fish outflank the dam on their way upriver. “The bypass has velocity conditions and depth conditions that we know pallids will use,” says Patrick Braaten, a research fish biologist with the U.S. Geological Survey whose studies helped inform the design. “It should be able to facilitate the passage of sturgeon that are motivated to migrate up the Yellowstone to spawn.”

Conservationists like Forrest, and many scientists, aren’t so sure. Sturgeon are notoriously difficult to coax through fish passages, and, as well designed as the bypass may be, proof that the fish will actually use the channel is scant. An independent report commissioned by the Corps itself cautioned that there exists “no evidence” that adult fish will find and use the bypass channel in “sufficient numbers to enable meaningful levels of spawning and recruitment.” And on July 28, the Upper Basin Pallid Sturgeon Workgroup, a collective of state and federal scientists working on the species’ recovery, penned a letter arguing that the benefits of the bypass channel were “purely theoretical.” (The letter, which had not been reviewed by senior officials at the U.S. Fish and Wildlife Service, was swiftly rescinded.)

Forrest’s preference is simple: tear out the Intake Diversion Dam altogether and let the fish migrate freely up the Yellowstone. Dam removal has proven time and again to help fish rebound. Among the alternatives outlined in the project’s final Environmental Impact Statement, published October 14, is a network of pumping stations that would remove water from the river, pass it through fish screens, and dump into irrigation canals — a dam-less solution that Forrest calls a “win-win.” A similar system appears to be helping green sturgeon bounce back in the Sacramento River, where the Bureau of Reclamation permanently lifted the gates of the Red Bluff Diversion Dam in 2012. “The scientific community has been clear that taking out the dam is the best possible thing we can do for pallid sturgeon,” says Brad Shepard, a fish biologist formerly with the Montana Fish, Wildlife and Parks Department.

But the pumps have one major drawback: their price-tag. According to the Impact Statement, pumps would cost $138 million to install — more than twice as much as the weir-and-bypass option — and another $2 million annually to maintain. Some of those expenses would be passed on to farmers, raising the cost of irrigation. Not only are pumps expensive, they’re unreliable, says James Brower, project manager for the Lower Yellowstone Irrigation Project, which relies on Intake’s water. Keeping a dam in place is vital to ensuring the region’s survival, he says: “The only way to help the pallid sturgeon without ruining six separate communities is to build the bypass channel.”

If irrigators and conservationists can agree on one thing, it’s that Intake has become a distraction from the more intractable — and far more expensive — fish passage and habitat problems on the mainstem Missouri. “It’s a lot easier to pick on 200 farming families than it is to pick on flood control in the Missouri River,” Brower says. The final public comment period for the Environmental Impact Statement is set to close in late November, and a decision could come soon thereafter. Whether wild pallid sturgeon survive for another 70 million years may hang in the balance.

Ben Goldfarb is a frequent contributor to High Country News, covering fish, wildlife and other conservation issues.