Spill water encourages sturgeon breeding

Test shows fish were forced to better area for laying eggs

Spilling water over Libby Dam may have aided endangered Kootenai River sturgeon this spring by coaxing the giant fish upriver to better spawning grounds.

The U.S. Army Corps of Engineers wrapped up the weeklong spill tests early Sunday. The pulse of water – designed to mimic historic spring flows – prompted some sturgeon to swim upstream to gravelly reaches of the river, according to preliminary reports. Biologists believe that fertilized sturgeon eggs have a better chance of survival in the gravels, rather than the sandy river bottom around Bonners Ferry, where the eggs get smothered by silt.

“We did see some spawning-age sturgeon above Bonners Ferry,” said Jason Flory, the U.S. Fish and Wildlife Service’s sturgeon recovery coordinator. In the past, “they’ve poked their nose above Bonners Ferry but they didn’t stay that long. …We’ll need the full data set” to determine what happened, he said.

Between 500 and 1,000 wild sturgeon are believed to remain in the Kootenai River. They haven’t reproduced successfully in the river since 1974, when the Libby Dam went into operation. Built for flood control and power generation, the dam tamed the river, reducing spring flows that once prompted the sturgeon to swim upstream from British Columbia’s Kootenay Lake to spawning grounds near Troy, Mont.

The aging of the wild females is a concern for biologists, Flory said. Although 20,000 young hatchery sturgeon have been introduced into the Kootenai River, they aren’t old enough to reproduce.

Kootenai sturgeon are a distinct stock, evolving after the latest ice age isolated them from Columbia River sturgeon. The freshwater giants can reach 8 feet in length, but they’re slow to mature. The fish don’t spawn until they’re 30 years old. Although females can live into their 70s, they lay eggs only every four to six years.

Some of the wild sturgeon are outfitted with radio transmitters, and their movements are recorded when they swim past six monitoring stations in the Kootenai River. Biologists will learn more about the sturgeons’ spawning journey later this summer, when river levels drop enough to retrieve data from the underwater monitoring stations, Flory said.

This was the third year that water was spilled over Libby Dam in an effort to move the sturgeon to better spawning grounds.

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