Monday November 17, 2025
Moscow-Pullman Daily News —
Fisheries managers on the Hells Canyon section of the Snake River are contemplating a future in which they may routinely move sturgeon and possibly boost their numbers through a hatchery program.
It would be a radical shift in management for a population that was once thought stable. But it’s one Joe DuPont, fisheries manager for the Idaho Department of Fish and Game’s Clearwater Region, believes is necessary to reverse a downward trend.
Giants of the deep
White sturgeon are one of the iconic animals of Hells Canyon and they are in trouble.
The population in the 137 miles of the Snake River between Hells Canyon Dam and Lower Granite Dam is not in imminent danger of collapse. But abundance trends have fisheries managers worried.
The population dropped by 33% between 2014 and 2025. While the number of big fish prized by catch-and-release anglers is stable, few juvenile fish are surviving their first year of life.
“There’s just this very serious and downward decline in the number of juveniles. And you cannot sustain a population if you cannot maintain the number of juvenile fish coming in,” DuPont said.
Sturgeon live decades and sometimes even reach the century mark. Mature fish that dwell in the deep blue pools of the canyon can weigh many hundreds of pounds and exceed 10 feet in length.
Along with bighorn sheep, they have come to be emblematic of North America’s deepest river gorge. Yet, unlike bighorns, few people ever see one. It takes specialized fishing gear and often a jet boat to catch these monsters that have been described as both prehistoric and living fossils because the species has existed for more than 175 million years.
In an interview with the Tribune, DuPont outlined a complex set of problems that has led to their decline. In short, construction of dams on the Snake and Columbia rivers has altered habitat and disrupted migration patterns. More recently, the biota of Lower Granite Reservoir has changed with the arrival of new species at the base of the food chain.
Missing juveniles
Data from a 2014 population survey conducted by Idaho Power indicated younger sturgeon were on the decline. DuPont and his team wanted to know more so they went looking for them with rods and reels.
“We couldn’t find any,” he said.
They also noticed that subadult sturgeon in Hells Canyon were stunted. DuPont said some are growing just a few centimeters a year — a rate so incremental that it is unlikely the fish will ever reach maturity.
The slow growth rates combined with poor survival of juvenile fish led them to believe that the free-flowing river has changed to the point that it no longer supports young fish. The Hells Canyon Complex of dams, built in the 1950s and 1960s, blocked the normal transport of sand and sediments downstream that provided habitat for aquatic insects and invertebrates. Downstream dams led to declines in salmon and steelhead that once returned by the millions and died after spawning. The decaying flesh of those fish provided a food source for sturgeon. The dams have also hammered lamprey, robbing young sturgeon that feed on the larval stage of the eel-like fish, an important food source.
“There is probably just not the food that these small fish need,” DuPont said. “It’s kind of alarming when you have 100 miles of free-flowing river and sturgeon less than 2 inches probably can’t survive in there.”
Slackwater
It’s a different story downstream in Lower Granite Reservoir.
“There is a lot of food and, if the conditions are right, they grow really well.”
But something else is happening there.
Idaho Power did some work in the reservoir to measure what biologists call recruitment — the survival of juveniles from hatching to their first year.
“The first three years they did their work, they found none,” said DuPont. “It was a shocker because in 1990 and 1991, they found all kinds of small fish.”
The lack of young fish persisted until 2017 when they measured good recruitment. But it was a one-year blip.
DuPont noted 2017 was a big water year with high spring flows. Looking back at data, they could see a pattern of little to no recruitment most years but better recruitment in years with high flows.
Entrainment
Historically, sturgeon moved up and down the Snake and Columbia rivers.” Juvenile fish are motivated to move downstream where the rivers are bigger, slower and there is more food available. Adult fish are motivated to move upstream to places like Hells Canyon where its deep pools with swift moving water provide ideal spawning habitat.
“Genetically, the Hells Canyon population is very similar to the Columbia population, which means they mixed at some point,” he said.
The dams now block upstream movement. The young fish can still move downstream through dams, known as entrainment.
To measure entrainment rates, fisheries biologists began catching and tagging young sturgeon in Lower Granite Reservoir.
DuPont now estimates that an alarming number of juvenile fish — 50% to 80% — migrate through the dam.
“It’s pretty much a one-way street,” he said. “Do some go through the locks? Yes, but not enough to sustain anything.”
Newcomers
DuPont and others wanted to understand why recruitment was limited to high-flow years.
It didn’t used to be that way. Between the 1990s, when sturgeon recruitment occurred in both high-water and low-water years, and today, new critters arrived in the reservoir.
Opossum shrimp, Siberian prawns and sand rollers have all either arrived for the first time, or greatly increased in abundance.
Shrimp — These small creatures measuring about one-half inch showed up in the Snake River in the 1990s and spread quickly.
“By the time we hit 2014, they were the most abundant epibenthic — small little creatures that live on the bottom,” DuPont said. “There were billions of those things out there.”
They are nutrient rich and used as a food source for just about any aquatic species that feeds on creatures of that size. They also happen to be about the same size as sturgeon during their first few weeks of life.
Prawns — Siberian prawns are from Asia and likely reached the Snake River in the ballast water of barges or other vessels. DuPont said they love opossum shrimp and have thrived since their arrival. He estimates there are tens to hundreds of millions of them.
“These small sturgeon are like a half-inch long when they hit the reservoir and it just happens to be that Siberian prawns’ main food, the opossum shrimp, is a half-inch long.”
Sand rollers — These small fish are native to the Columbia Basin but there were few in the lower Snake River until the late 1990s. Now there are millions. Like Siberian prawns, they capitalized on opossum shrimp and DuPont believes they now eat young sturgeon as well.
His theory is that prawns and sand rollers feast on tiny sturgeon during their first few weeks of life. But once sturgeon reach a few inches in length, they can escape the predators.
So what does high water have to do with it? During high-flow years, DuPont surmises sand rollers and Siberian prawns, both poor swimmers, get pushed to the sides and slower-moving areas. That gives young sturgeon in the deep pools a little bit more time to grow to the point they are no longer vulnerable.
“If a sturgeon can get over like 1 or 2 inches, there is just a plethora of food. They can turn around and eat those opossum shrimp, and then when they get bigger they can eat the Siberian prawns and the sand rollers.”
Fish movers
A few years ago, Idaho and other sturgeon managers started catching slow-growing subadult sturgeon in Hells Canyon and moving them downstream to the reservoir to see if they would benefit. Ideally, they would grow in the reservoir for a few years and reach a size where they can continue to grow if and when they move back to Hells Canyon. It worked.
“These sturgeon that we’re recapturing in the reservoir are growing 20 to 40 times faster than the fish in the river,” he said.
On the downside, some of the fish took the opportunity to move farther downstream.
More recently, fisheries managers started a pilot project catching mature sturgeon below Lower Granite Dam and moving them upriver, where it is hoped they will spawn. About 40 were released in the reservoir and another 40 at Heller Bar. It’s early, but DuPont said some of the fish released at Heller Bar have already started to move upstream.
Problem solved?
Even if moving fish upstream and downstream expands from an experiment to an annual program, DuPont said it likely won’t be enough.
“At least since 2013, we’ve only had one year where there’s been meaningful recruitment,” he said. “Even if you moved every fish that entrained up and every slow-moving fish down to maximize that population, you can not sustain it on one year of recruitment out of every 15 years.”
He wants the region to start looking into a hatchery program. Under ideal circumstances, they would be able to collect fertilized eggs and larvae from the river, bring them into a hatchery and release them weeks, months or maybe even a year later.
“The beauty of that is you allow natural selection.”
If they can’t collect enough eggs and larvae, they might need to employ a more traditional hatchery program where adults are trapped, spawned and then released. The downside of that is humans are directing spawning instead of nature.
He’d like to see experiments to see if enough eggs and larvae can be collected. He noted when Idaho, Oregon and Washington moved to catch-and-release fishing only for sturgeon in 1970, it took about 40 years for the population of adult sturgeon to stabilize.
“I don’t want to go back and have to reset for another 40 years or more.”