BOISE, Idaho (AP) — The population of North America’s largest freshwater fish living between a dam on the Idaho-Oregon border and another in western Washington state was holding steady from 14 years ago, according to preliminary information from an Idaho utility’s survey.

White sturgeon, which date to the dinosaurs, number about 4,000 in a 140-mile stretch of the Snake River between Hells Canyon Dam and Lower Granite Dam. That tally counts fish measuring 2½ feet or longer.

Idaho Power is required to monitor numbers of sturgeon there as part of its federal license to operate three hydroelectric projects in Hells Canyon.

Preliminary information from the utility’s three-year survey that ends in September shows the population is about the same as found by a previous survey 14 years ago, Idaho Power fisheries biologist Brandon Bentz said.

Dams on the Snake River have isolated populations of sturgeon that historically moved up and down the river, even entering the Columbia River and reaching the Pacific Ocean, experts say. The dams also reduced food sources such as salmon, steelhead and lamprey and made water temperatures colder below Hells Canyon Dam.

Sturgeon can weigh more than 1,500 pounds and reach about 12 feet. The toothless, bottom-dwelling fish date to the dinosaurs and have rows of armor projections along their bodies.

The stretch of river from Hells Canyon Dam to Lower Granite Dam is a favorite among sturgeon anglers, said Jeff Dillon, fisheries manager for Idaho Fish and Game.

“For one, it’s just fascinating to catch a fish that’s probably older and bigger than you are,” he said. “And they’re prehistoric fish. The other part of it, especially in Hells Canyon, is fishing for sturgeon takes you to really amazing places.”

One of the sturgeon in the Snake River is a 470-pound, 10-foot female caught and released last month as part of Idaho Power’s survey. Bentz said the length of the fish is rare and estimated it to be about 75 years old.

Angling regulations in Idaho, Oregon and Washington require barbless hooks and that sturgeon be released unharmed. Dillon estimates that sturgeon in Hells Canyon are caught on average once or twice a year.

“We don’t see any real evidence of ill effects,” he said. “They’re pretty resilient fish.”

The Snake River has two self-sustaining populations of sturgeon. One is Hells Canyon and the other is the section of river between Bliss Dam and C.J. Strike Dam in southern Idaho, Bentz said. A sturgeon measuring just under 11 feet was caught there by an Idaho Power crew in the early 1990s, but it wasn’t as heavy as the more recently caught fish, Bentz said.

There is still much that is not known about sturgeon between Hells Canyon Dam and Lower Granite Dam. Biologists don’t capture many smaller fish, so their growth rates or survival rates aren’t known, Bentz said.

It also is not known how many sturgeon lived in that part of the river before dams were built or how many fish it could support now.

Sturgeon eat bottom-dwelling worms, clams, mussels and crayfish. Though salmon aren’t as prevalent as before the dams, they are still a food source, especially nests containing salmon eggs, Bentz said.

The rarity of the 10-foot fish recently caught by Idaho Power begs the question: Why aren’t there more of them?

“The (catch and release) rules have been in place for only 40 years,” said Dillon of the wildlife department. “It could be 100 years before there are a lot of fish over 10 feet out there.”

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