Nine breeding-age pallid sturgeon are swimming in circles at the Garrison Dam National Fish Hatchery in Riverdale, and biologists hope to get 400,000 eggs to help grow more of the endangered fish.

The six males and three females range in weight from almost 60 pounds to a couple in the mid-30-pound range, hatchery manager Rob Holm said Thursday.

"They all are about 50-year-old fish, born about the time the dam was completed," he added.

U.S. Fish and Wildlife Service researchers caught 28 pallids in the vicinity of the Missouri and Yellowstone rivers during two recent trips. Other pallids went to the Miles City, Mont., National Fish Hatchery.

Of those 28 pallids that biologists netted, only three hadn't been caught before.

"Some have been caught four, five, six times," said Steve Krentz, a USFWS fisheries biologist in Bismarck, who was among those netting the brood stock.

Before starting the spawning process, Holm hopes to have the genetics of each recaptured pallid sorted out. Pieces of their fins are being sent to a laboratory in Washington for analysis.

"They can tell me which ones are least related, and we will pair those up," he said.

With a pilot and plane available in Miles City, the two hatcheries can trade milch, if it becomes necessary, Holm added.

Of the nine pallids in Riverdale, only one, a female, had not been caught previously.

"The other female was spawned in 1997 at Garrison, first year we started spawning," Holm said.

Although the third female is mature, her eggs are immature, and "she probably will be tagged and put back in the river," Holm said.

Netting brood stock to raise pallids in hatcheries is part of USFWS biologists' efforts to bring the prehistoric fish back from the edge of extinction.

The USFWS estimates only about 200 breeding age pallids are alive in the stretch of the Missouri River system between Fort Peck, Mont., and Lake Sakakawea.

"We've been tagging fish since the late '80s, and in almost 18 years of tagging we've seen almost all of them, which is kind of a scary thought," Krentz said.

Pallids probably live up to 60 years in the wild.

"Of the ones we caught, probably the majority were 40 to 55 years old. It doesn't take much mathematics to figure out if the top age is 50 to 60 that these fish will be moving off the top end of the population in the near future," Krentz said.

Releasing hatchery-raised pallids in the upper Missouri River system began with the 1997 year class, but even those small pallids are years away from spawning age.

"It probably will be another 10 years before those juveniles become sexually mature," Krentz said.

Researchers are making plans to go after more breeding sized pallids, possibly next week.

Each spring netting trip for pallids brings new twists.

"We saw everything from 70 and 80 degrees, to below freezing, to blowing wind and rain," Krentz said of his two trips this spring. "We were up there when the blizzard hit. We kept on going."

Up to 20 people and five or six boats were involved in the captures.

"Typically we get them in the confluence," Holm said. This spring, "a little bit of pulse had triggered their movement up the Yellowstone, and it made capture more difficult.

"You think you've got it figured out, and they always throw you a curve."

(Reach outdoor writer Richard Hinton at 250-8256 or richard.hinton@;bismarcktribune.com.)