Sacramento River salmon at highest population level in 24 years

DON THOMPSON Associated Press

SACRAMENTO - Wildlife managers expect more than 15,000 endangered winter-run chinook salmon to thrash their way up the Sacramento River this year, the largest number in 24 years thanks to extraordinary and expensive efforts to save the species.

But there are a couple of caution flags: An unusually high percentage of the returning fish were born in a hatchery, while an improbably low proportion of dead male fish were found by biologists counting carcasses of the salmon, which die after breeding.

An estimated 18 percent are hatchery fish this year, up from the usual 5 percent to 10 percent. Biologists limit the number of hatchery fish to avoid contaminating the wild gene pool, but an unusually large number were released three years ago as an experiment.

"It looks like the hatchery fish may have survived a lot better this year. We're not really sure why," said Alice Low, a senior fishery biologist with the state Department of Fish and Game. "It's definitely something we'll keep an eye on."

Hatchery releases have since been more limited, she said, so biologists don't expect it to be a long-term problem.

In addition, scientists counting dead salmon have found proportions as high as seven females for every male.

That may stem from differing behavior, Low said. Males tend to leave after spawning and so aren't around to be counted when they die, while females tend to stay in the shallow spawning area and are more easily recovered.

Biologists think the real ratio is closer to 60 percent female and 40 percent male.

"As far as we know, all the eggs are being fertilized, so we don't think we have such a skewed sex ratio that that's a problem at all," Low said.

The ratio is important as well to the winter run's future under the Endangered Species Act. Officially, the run will be considered recovered if more than 10,000 females return to spawn each year for 13 years.

As recently as the 1960s, more than 50,000 fish returned each year. But the world's southernmost chinook population had shrunk to just 186 fish by 1994, before recovery efforts began.

The Sacramento River is unique in having evolved four separate salmon runs, when the oceangoing fish return to their birthplace to breed and die. But the winter run had the misfortune of spawning in midsummer, when the river becomes too warm.

That wasn't a problem when the fish could swim to cool mountain streams. But in 1945, Shasta Dam cut off their migration north of Redding and their numbers eventually dwindled. The fish now spawn only between Redding's Keswick Dam and the Red Bluff diversion dam.

Since the population collapse, the government has spent more than $280 million to alter Shasta and other dams, to clean up pollution from the Iron Mountain Mine near Redding, and to screen irrigation pumps that used to suck salmon into farmers' fields. Of that, $80 million went for temperature control devices that let cool water flow from Lake Shasta to nourish the eggs.

"Up to 50 percent of the eggs may have been killed by temperature in any given year. That doesn't happen anymore," said Low. Now, less than 1 percent are believed to die because of temperature problems.

Iron Mountain once spewed the world's most acidic mine drainage and the nation's highest concentration of toxic metals into the river just below Shasta Dam. But that also is increasingly contained at a cost eventually expected to reach $1 billion.