[3] Snake Fall Chinook Return Beats 10-Year Average

There has been little fanfare this year for the Snake River fall chinook run, which though down from recent years, is still coming in strong compared to returns from the 1990s.

So far, about 8,000 chinook (hatchery plus wild) have returned, according to the count at Lower Granite Dam. That's nearly one-third below the average for the last six years, but still a major improvement over the 1990s--this year's count is 16 percent above the 10-year average

The overall numbers have been helped in recent years by significant returns of fish raised in hatcheries and out-planted in the Snake at several sites as juveniles, which has given fish managers major problems in trying to determine just how many returning chinook are truly wild. That's always been a tough question to answer, and the managers aren't ready this year either. In fact, they still haven't figured out how many wild fish made it back to Idaho in 2004 and 2005.

Wild chinook returns hadn't passed the 1,000-fish mark from 1975 until 2000, when 1,148 were estimated to have returned. Since then, the numbers have been even better, with a 5,000-fish return in 2001, 2,100 in 2002 and 3,900 in 2003.

With an interim recovery goal of 2,500 spawners set by NOAA Fisheries some years back, it seems the fall run is well on the road to recovery. And if the wild run is in the same proportion it showed in 2003, when the last estimate is available, it's likely to be around 2,600 fish--a number still beating the interim recovery goal in a year when returns for fall chinook throughout the Columbia River Basin are down.

In 1990, only 78 wild fall chinook were estimated to have returned to Idaho. Their numbers had declined steadily since the 1960s, after three-fourths of their habitat was blocked by construction of Idaho Power's Hells Canyon Complex. The stock took more hits when lower Snake dams were built.

Most biologists attribute the boost in the wild run to the success of a supplementation effort focused at Lyons Ferry, where fish are raised, and then trucked above Lower Granite to acclimation ponds. Fall chinook are also released from the Nez Perce Hatchery on the Clearwater River, and have been allowed to return to spawn there, where no fall chinook run previously existed, a situation likely due to the extremely cold water compared to traditional spawning grounds in the lower Snake.

In recent years, it's been discovered many of these fish stay in reservoirs and the estuary for the entire winter, and migrate before pit-tag detectors are turned on at dams in the spring. It has confounded survival studies for fall chinook, since many of the undetected fish were originally thought to have died.

But lately, researchers have examined scale samples from returning adults and found the late migrators seem to survive at a much greater rate than the sub-yearlings.

In a peer-reviewed report released as the first product by a new group of independent scientists taking over for the analyses previously performed by the Fish Passage Center, recent research has found that reservoir-type fall chinook "made up a small fraction of the juveniles (about 5 percent based on detection histories)," and "accounted for about half of the returning adults."

The report also found that while ocean-type (sub-yearling) chinook numbers roughly match those of reservoir-type fall chinook in the returns of hatchery-origin adults, they are more prevalent in the return of wild-born adults. -B. R.

Subscriptions and Feedback
Subscribe to the Fishletter notification e-mail list.
Send e-mail comments to the editor.

THE ARCHIVE :: Previous NW Fishletter issues and supporting documents.

NW Fishletter is produced by Energy NewsData.
Publisher: Cyrus Noë, Editor: Bill Rudolph
Phone: (206) 285-4848 Fax: (206) 281-8035