BOISE, Idaho – Each year, endangered white sturgeon lay millions of fertilized eggs on the silty bed of the Kootenai River in the Idaho Panhandle. Yet experts estimate only 10 of the sturgeon hatched from those eggs survive.
The white sturgeon, the largest freshwater fish in North America, has not successfully reproduced in the Kootenai since Libby Dam was completed in Montana in 1974, reducing the river velocity and trapping critical nutrients upstream.
Downstream, however, pools at a hatchery run by the Kootenai Indian Tribe teem with thousands of year-old sturgeon, inch-long replicas of the two armor-plated wild adults in another tank, each measuring 6- or 7-feet long. Another tank holds medium-sized fish raised at the hatchery since birth.
Bred from captured wild sturgeon, the young sturgeon may represent the last hope biologists have of preventing the species' extinction. An estimated 500 wild sturgeon remain, a number expected to dwindle to 50 by 2030 unless scientists find a way to encourage successful reproduction.
"Old sturgeon don't die, they just fade away," said Sue Ireland, the fish and wildlife program manager for the Kootenai Tribe.
Over the past decade, the hatchery has released 80,000 juvenile sturgeon into the river. But since the fish do not reach sexual maturity until about age 30, the oldest of those hatchery-raised sturgeon are not expected to begin spawning until 2025.
The first year the fish are released, about 60 percent survive, said Bob Hallock, Kootenai white sturgeon recovery team leader for the U.S. Fish and Wildlife Service.
"After that, the rate is about 90 percent annually, so you play that out over 30 years and that's not a lot of fish," he said.
Ireland said researchers are unsure whether the hatchery fish will return to the place they were born, as oceangoing salmon do, or spawn elsewhere along the only place they are found — a 167-mile stretch of river between Kootenai Falls in Montana across Idaho to Corra Linn Dam at the end of British Columbia's Kootenay Lake.
Researchers would like them to return to an 18-mile section of the river in Boundary County that has been designated critical habitat by the Fish and Wildlife Service.
The designation means federal and state agencies must consult with the service before undertaking projects that might affect the sturgeon, which were declared an endangered species by the federal government in 1994.
The habitat designation also means that Libby Dam operations must be modified to better replicate the higher, faster flows of the Kootenai before the dam.
It's estimated that releasing more water from the dam to accommodate the sturgeon in that section of the river will cost between $360 million and $780 million from now until 2025, when the first hatchery bred sturgeon may start to spawn.
Biologists say the river is moving more slowly than it did before the dam, allowing silt to fill the river bottom and cover rock crevices where young sturgeon can hide from predators. They believe increasing flows and velocity would clear out sand and silt from spawning beds, providing a gravelly place for fertilized eggs to incubate.
"The fish have been going to a certain location near Bonners Ferry and laying eggs, but they don't have the substrate to adhere to," said Tom Buckley, spokesman for the Fish and Wildlife Service in Spokane, Wash. "If we did have any successful hatching, right now there's no place for the young fish to hide in that location."
The Service is proposing that the Army Corps of Engineers install rocks and gravel in the river downstream from Bonners Ferry, along with potentially dredging and narrowing the channel while raising the river banks.
Some of the habitat improvements will begin this summer.
"The question is, are the thousands of hatchery fish we've released going to return to a habitat 30 years from now that is functional for reproduction?" said Hallock.