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Scientists saving pallid sturgeon in Montana still face hurdles

Tanner Cox releases a pallid sturgeon on the Yellowstone River. Scientists working to preserve the fish have made great strides but still face a few hurdles to recover the endangered species. (USGS / Courtesy)
Tanner Cox releases a pallid sturgeon on the Yellowstone River. Scientists working to preserve the fish have made great strides but still face a few hurdles to recover the endangered species. (USGS / Courtesy)
By Brett French Billings Gazette

BILLINGS – A bevy of scientists has helped Montana’s most threatened fish avoid blinking out.

Declared an endangered species in 1990, there are only about 100 wild adult pallid sturgeon living in the Missouri and Yellowstone rivers above Lake Sakakawea. About half as many are believed to inhabit the Missouri River above Fort Peck Reservoir.

But swimming in those same waters are roughly 19,000 of their offspring, all brought to life thanks to human intervention via a hatchery program.

“I’m happy to announce that extinction has been averted,” said Bob Snyder, of the Upper Basin Pallid Sturgeon Workgroup.

The stocking program, fueled by eggs collected from wild fish, allowed the preservation of the fishes’ unique genetics and spread several generations of pallids across the river systems, buying scientists time.

Although worthy of a biology high-five, challenges for the fish continue to exist, the largest being a lack of natural reproduction and the continued presence of dams that have substantially altered their ecosystem.

Old fish

When it comes to fisheries biology, pallid sturgeon present one of the most difficult freshwater challenges. The fish are long-lived, capable of lengthy spawning migrations, yet wild reproduction in the Missouri and Yellowstone rivers in Montana has been rare due to dams.

Scientists from an alphabet soup of federal and state agencies, along with graduate students, have teamed up to learn about and help the species. They’ve made great strides.

Snyder was one of several speakers addressing fellow Montana fisheries professionals and students at an annual gathering of the Montana Chapter of the American Fisheries Society in Billings last week. For 19 years he’s worked on pallid sturgeon recovery.

Upper Missouri

From stocking a lot of fish early in the 1990s, the hatchery program now emphasizes genetic variation in the fish stocked – artificially preserving the genes of the last remaining wild fish.

Now the question is whether all of those hatchery planters can reproduce. In 1998 the first pallids were stocked above Fort Peck Reservoir on the Missouri River. Those fish have reached reproductive adulthood – 2011 for males and 2015 for females – yet there’s been no documented reproductive success by the fish in the wild.

Three fish did spawn, according to Tanner Cox, of the Montana Cooperative Fish Research Unit, who studied pallid sturgeon in the region. But the fish are not spawning far enough upstream for their larvae to survive. Instead, the immature fish typically drift into the head of Fort Peck Reservoir and die.

Captured female adult pallids that were hatchery-reared are also showing a high tendency to reabsorb their eggs rather than spawn. Because so many are suffering the same fate, Cox said scientists suspect it could be due to environmental factors, perhaps water temperature.

Out of the 16 years of classes of pallid sturgeon released in the upper Missouri, growth rates of younger year classes seem to be low, according to Luke Holmquist, a Fish, Wildlife and Parks fisheries biologist based in Lewistown. That may be due to overstocking, he speculated.

What’s more, 80 percent of the older stocked fish are still immature at age 19 – years later than the age of maturity for wild fish.

Lower Missouri

Downstream, on the Missouri River below Fort Peck Dam, scientists confront a different challenge.

“Our spring freshet has been muted in normal (dam) operating years,” according to Tyler Haddix, an FWP fisheries biologist in Fort Peck.

Spring runoff is key to urging pallid sturgeon upstream to spawn. Water released from Fort Peck Dam, however, is often cold since it is coming from the bottom of the reservoir. Cold water means pallid sturgeon larvae mature more slowly.

FWP would like the Army Corps of Engineers, which operates the dam, to dump water down the spillway to mimic spring runoff conditions to attract fish upstream to spawn. That hasn’t happened except in years of high water. FWP has given the Corps a hydrograph suggesting ways to mimic runoff that may benefit pallids.

“We have to keep pushing,” Haddix said.

Yellowstone River

The pallid sturgeon in the lower Yellowstone and Missouri rivers live most of the year near the confluence of the two streams. In the spring, depending on runoff, they will decide which river to swim up to spawn. Usually, that’s been the Yellowstone, since its flows are not dam controlled.

But only 71 miles upstream is Intake Dam, which blocks pallids from swimming any higher. The exception is in high water years, when a side channel is flooded allowing fish to swim around the dam.

In 2014, a wild pallid female went up the side channel and 20 miles up the turbid Powder River – the first time such a migration was documented by FWP. Two male pallids followed shortly after, but didn’t ascend the Powder River as far. Whether the fish successfully spawned is unknown. The mouth of the Powder River is at mile 149 – 78 miles above Intake Dam.

In 2017, two male pallids migrated 96 miles up the Powder River – roughly 250 miles from the confluence and 300 miles above the mouth of Lake Sakakawea. In 2018 four hatchery-raised males moved upstream, one stopped at about river mile 235, just below Cartersville Dam on the Yellowstone River.

The documented movements have given Mike Backes, FWP fisheries manager in Miles City, hope that the fish may one day successfully spawn.

“The distance these fish are going is quite impressive,” he said.

One fish, tagged by Backes in 1994, is still alive.

“It’s been 24 years and this fish is still teaching us,” he said. “These fish are exceeding our careers.”

The big question looming is how the upcoming rebuild of Intake Dam and its associated man-altered side channel will affect the upstream fish migrations.

“I believe pallid sturgeon in Montana can be recovered” if scientists get the support they need, Snyder said.

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