The largest number of coho salmon in a decade have returned to tributaries of the Russian River to spawn, which bodes well for a fish that was on the verge of extinction, biologists said.

California Fish and Game scientists estimate 190 coho salmon, which are listed on both state and federal endangered species lists, returned during the spawning run of last October to December.

"It is a tremendous increase. The total number the year before was less than 20," said Dave Manning, a principal environmental specialist for the Sonoma County Water Agency.

It is an indication that a coho broodstock program that began in 2001 has been successful, said Brett Wilson, who supervises the program at the Don Clausen Hatchery at Warm Springs Dam.

"If we didn't act when we did, according to what we saw, potentially they could have been lost forever," Wilson said.

Coho, which comes from the Russian "kizhuch," are the most fragile of the three fish that are in trouble in the Russian River watershed. The two others, chinook salmon and steelhead, are on the threatened list.

"Coho need the coldest water, they reside in the western portion of the watershed that has denser vegetation, their habitat range is not as broad as steelhead and chinook, and they are in a rigid three-year life cycle," Manning said. "So they are susceptible to habitat degradation or natural events like drought or flood or changes in ocean condition."

Coho spawn in Russian River tributaries, including Austin Creek, Dry Creek, Dutch Bill Creek and Mill Creek.

The young will go to the Pacific Ocean and return to spawn three years later as adults, weighing from 7 to 12 pounds.

In 2001, the hatchery program began as an emergency measure to keep coho from going extinct, using 200 to 300 wild fish that were found in the tributaries during the three years that followed, said Fish and Game biologist Ben White.

In 2004, however, they found just a few. Russian River coho, in biologists' jargon, had "blinked out."

Those first few fish were bred, raised and the offspring released into the tributaries each year in increasing numbers. All fish are also sorted and bred using DNA samples.

The first release was 6,000 fingerlings in 2004, but that has been increased each year to the 170,000 that were released last year.

The hatchery program is funded by the U.S. Army Corps of Engineers, at $700,000 a year.

The water agency also contributes $100,000 annually to the hatchery program, has spent $1 million in studies on Dry Creek and will spend an estimated $5 million to $8 million for Dry Creek habitat projects.