Recovery of the Pallid Sturgeon

For more than 30 years, funding has been provided for research, equipment and personnel to help recover the pallid sturgeon from endangered listing.

Pallid sturgeon live nearly as long as humans, 60 to 75 years. However, their reproduction is incredibly slow.

It takes about 20 years for a pallid sturgeon to reach sexual maturity, and then females only spawn about once every four years. After hatching, pallid sturgeon larvae require specific conditions in order to survive. When pallid sturgeon eggs hatch, the larvae begin swimming frequently and higher up from the river bottom.

“When they swim up, they get caught by the current, and they move downstream pretty fast,” explained Grant Grisak, Biologist with NorthWestern Energy.

That downstream drift is critical to pallid sturgeon survival. They need to drift for about 180 miles.

Historically, pallid sturgeon used the entire length of Missouri and Mississippi rivers. The larvae from a fish that spawned in Montana might drift as far as Iowa. Then, when it reached maturity, that fish would likely come back to Montana to spawn.

“They could basically go all the way from Montana to the state of Missouri,” Grant said.

Pallid sturgeon larvae need to drift downstream for about 180 miles.

When the large flood-control dams were built on the Missouri and Mississippi rivers, it fragmented the habitat of pallid sturgeon and greatly shortened adult habitat segments and larvae drifts. That, combined with over-fishing, took a hard toll on pallid sturgeon, driving them nearly to extinction, resulting in the species being listed under the federal Endangered Species Act in 1990.

For 32 years, funding has been provided for research, equipment and personnel to help recover the pallid sturgeon from endangered listing. Recovery efforts have included stocking hatchery-raised pallids in the Missouri River starting in 1997.

NorthWestern helped transport about 800,000 pallid sturgeon eggs from a hatchery in South Dakota to the Miles City, Montana, hatchery.

Although recovery efforts for pallid sturgeon have been in the works for more than three decades, progress moves slowly when fish only spawn once every four years.

“You can see why it takes so long to perpetuate these fish,” Grant said.

This spring, NorthWestern Energy, Fish, Wildlife & Parks and the Bureau of Reclamation determined flows in the Marias River, a tributary to the Missouri, would be high enough to conduct a larval drift study. During the study, pallid sturgeon larvae were released in the Marias at sites that mimic likely spawning locations. Then, water was sampled at increments downstream to determine how far the larvae drift and how many survive.

“If you can prove they survive all the way down, it’s hopeful that drift distance is sufficient enough,” Grant said.

There were also fish eggs available for the study. A hatchery in Gavins Point, South Dakota, near Yankton, had 40 female sturgeon who were ready to spawn. However, state and federal employees were under travel restrictions at the time, so they weren’t able to travel to bring the fish eggs to Montana. Luckily, the NorthWestern Energy biologist was able to take the nine-hour drive from his home in Great Falls, Montana, to Rapid City, South Dakota, where he met workers from the Gavins Point hatchery. In a Rapid City parking lot, Grant loaded some 800,000 pallid sturgeon eggs, spawned two days earlier, into his truck and drove them to the fish hatchery in Miles City, Montana.

One million pallid sturgeon eggs were transported from South Dakota to Montana for a larval drift study.

A few days later, those eggs hatched and the fish were released in the Marias River, giving them about 200 miles of drift before they reached Fort Peck Reservoir.

Biologists then traveled downstream to collect water samples and determine if any of the larvae survived. The biologists, however, were in for a pleasant surprise.

A week after the release, while working at Robinson Bridge on the Missouri River, about 155 miles downstream from the release site, 10 radio-tagged pallid sturgeon showed up in a pool of the river, along with an unknown number of non-radio-tagged fish.

NorthWestern Energy Biologist Grant Grisak holds a pallid sturgeon in the Missouri River.

“It was clear they were in the act of spawning,” Grant said. Seeing these spawning pallid sturgeon was an incredible sight; not long ago, there weren’t enough mature fish in the river to get together and spawn.

In 2019, NorthWestern Energy worked with other agencies to sample for pallid sturgeon larvae in the Marias and Missouri rivers. They found two larvae in the lower Missouri River, a sign the fish were in fact successfully spawning.

“The next link is to determine whether their progeny can survive,” Grant said. “That’s the mark of recovery – when you can develop a self-sustaining population.”

By Erin Madison