Kim Fundingsland/MDN An adult pallid sturgeon swims in a large holding tank at the Garrison Dam National Fish Hatchery. The fish was artificially spawned in 2016.

Twenty or so years ago, an estimated 400 of them were believed to exist in the wild. Today that estimate has declined to 125 or fewer. Without taking action now, say federal wildlife officials, wild pallid sturgeon are destined for extinction in the Yellowstone River system forever.

A federal judge blocked a proposed irrigation dam and fish passage that was proposed to be constructed on the Yellowstone River near Glendive, Mont., in 2015. The fish passage, contends the USFWS, would allow the remaining prehistoric pallids to reach their spawning grounds in the upper reaches of the Yellowstone. Currently a rock weir that has been in place for decades has prevented pallids from moving upstream. The proposed dam and fish passage would replace the weir and still allow for ample irrigation for cropland in the area.

U.S. Fish and Wildlife Service Assistant Regional Director Michael Thabault said in a court document filed in Billings, Mont., Wednesday that putting off the project any longer will likely “cost the lives of many of the last wild pallids” and that the loss would forever remove “that fish’s potential contribution to the recovery of the species.”

Adult pallids reach up to six feet in length and take 15 years or more to reach breeding age. They are a long-lived fish that can exceed 50 years of age. However, with no natural spawning documented since dams have been constructed on the Yellowstone, pallids are growing old and dying without reproducing. As a result, the pallid sturgeon was placed on the Endangered Species List in 1990.

The Garrison Dam National Fish Hatchery has been a focal point for hatching and rearing pallid sturgeon in order to keep the species from extinction in the Yellowstone River system. Project Leader Rob Holm has been instrumental in the artificial spawning of pallids, a necessary endeavor to prevent the Yellowstone pallids from disappearing forever.

“We’ve raised and released over 250,000,” said Holm. “The first fish went out of here in 1997 but we really got started in 2001. We’ve probably done more than half of the stockings of pallids in the world.”

The young pallids have been released into the wild. A few have been returned in test nets and such, an indicator that the released pallids are surviving. However, there has been no documented recruitment from the released fish, the first of which are just reaching breeding age. It is believed they will suffer from the same travel restrictions on the Yellowstone as their wild parents, meaning hatchery raised pallids may soon become the only survivors of the species in that river system.

Teams of fish biologists gather near the confluence of the Missouri and Yellowstone rivers each spring for the purpose of netting adult fish. Those fish are transferred to the Garrison Hatchery where they will be artificially spawned. Catching new pallids for the project is rare. Last year was an exception with two pallids not previously known to biologists among those transported to the hatchery.

“We usually catch the same ones,” remarked Holm.

Capturing wild pallids has become somewhat easier in recent years. That’s because biologists have been able to locate pallids that had previously been captured and outfitted with tiny radio transmitters. It also has helped biologists find dead pallids, likely fish that had reached the end of their life span.

The U.S. Army Corps of Engineers wants to start construction on the dam near Glendive in April. Any later than that, says the Corps, and funding for the project will likely be allocated elsewhere. It is not known how soon the USFWS will receive a response to their latest request to the court. District Court Judge Brian Morris blocked the proposal in response to a lawsuit from the Montana-based Defenders of Wildlife and the Natural Resources Defense Council.