BOISE, Idaho (AP) — Federal officials are revising a 1999 plan as part of a strategy to recover endangered white sturgeon in the Kootenai River in northern Idaho and western Montana.

The U.S. Fish and Wildlife Service is taking public comments through July 29 on the draft recovery plan revisions released last week.

The document reflects advancements in understanding of white sturgeon and changes that have taken place over the last two decades intended to help the prehistoric fish rebound.

“The old plan had become woefully out of date,” said Jason Flory, a biologist with the U.S. Fish and Wildlife Service.

White sturgeon are also found in the Columbia River, but the Kootenai population is genetically distinct after being isolated since the last Ice Age. Sturgeon have been around since the dinosaurs, have armor-like scales, and feed on clams and other bottom-dwelling organisms. Flory said the Kootenai River sturgeon have been recorded up to 10 feet (3 meters) long.

There are 24 species of sturgeon worldwide, and most are threatened with extinction.

The Kootenai River population has struggled since the completion of Libby Dam in Montana in 1974, which altered the natural cycle of the river.

The hydroelectric facility is run by the Army Corps of Engineers and serves power markets in the Pacific Northwest. The dam stopped periodic flooding of Bonners Ferry, Idaho, which is in a historic alluvial flood plain. Those same high-water flows triggered sturgeon to move upriver to spawn.

The federal government last decade agreed to alter how it runs the dam and more closely mimic historical water flows to benefit sturgeon following lawsuits from environmental groups. But it’s still less than half of historic levels.

Historically, the fish are known to have spawned below Kootenai Falls in Montana in rocky areas. After the dam, the fish started spawning in sandy-bottomed areas near Bonners Ferry, which isn’t conducive to egg survival. According to studies, the river in that area has always had that composition.

That area is part of an 18-mile (29-kilometer) section of the river that’s been designated by federal authorities as critical habitat for sturgeon. Some work has been done in the area to make spawning success more likely.

It’s not clear why the fish picked that area to spawn, said Flory.

Speculation includes the river in that area having deep, turbulent pools the fish favor. The prevalence of such pools might have diminished since the dam was built, cutting off high spring flows that scour the river bottom.

Another thought is that the dam removed turbidity from glacial sediment and made the river clearer, and the fish don’t feel safe moving upstream through shallow areas where they can be seen.

Part of the current strategy, Flory said, is to make the current spawning area more conducive to egg survival, and make river conditions more likely to get some fish to start using the historic spawning area.

Specifically, the six-part strategy in the revised recovery plan includes raising sturgeon in hatcheries, controlling flows from Libby Dam, adding nutrients to the river that are lost behind Libby Dam, restoring habitat where possible, monitoring and public outreach. Estimated cost for that work is about $7 million to $12 million annually.

The Kootenai Tribe since the mid-1990s has released more than 280,000 hatchery-raised sturgeon into the river.

“That’s basically staved off extinction,” Flory said.

The area is thought to have once had about 10,000 sturgeon. The document said the fish could be removed from endangered status if they become self-propagating. But the long-lived fish — up to a century — don’t become sexually mature until about age 25. The document said the earliest that delisting might occur is 2058.

Flory said the draft revision plan is part of a process leading to a document called the recovery implementation strategy that will have more specific details about potential actions to help sturgeon. He said work on that document could begin this year.