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NW Fishletter #232, June 14, 2007

[1] 2006 Juvenile Fish Survival Best In Years

Juvenile fish survival through the federal hydro system in 2006 was the highest in years, about 61 percent overall for Snake River spring chinook, according to a draft report released last week by NMFS.

That's the best news since 1999, when they began to make such precise estimates--thanks to the installation of PIT tag detectors at most federal dams.

The news was good for steelhead as well. They showed the highest juvenile survival since 1999--about 42 percent.

The tagged chinook used in the studies were mostly from hatcheries--92 percent, as opposed to only 8 percent wild fish in the release groups. About 62 percent of the steelhead were hatchery fish, 38 percent wild.

Even though fewer spring chinook were barged in 2006 compared to previous years in order to "spread the risk," about 60 percent of them were still transported, along with 75 percent of the tagged steelhead.

Upper Columbia chinook survival ranged from 42 percent to 55 percent, while steelhead survival from that part of the basin ranged from 18 percent (Cassimer Bar Hatchery) to 60 percent (Turtle Rock Hatchery, Wenatchee River).

The high survival in 2006 came in a year of plentiful flows, when the Columbia Basin water supply was 106 percent of average. Flows last year, especially in April, were good, but they dropped off in early May, then rose quickly to top out by the third week of the month. Also, there was more spill at the dams than any of the previous six years.

Young salmon may have also been able to hide better from predators during their downstream trek--turbidity was much higher in 2006 than normal.

However, in 2005, when the basin faced a 76-percent average snowpack, agency scientists estimated survival at 53 percent, similar to results in the 2002 and 2003 migration years.

In 2004 and 2005, transport was maximized, which means there was little spill at lower Snake dams to aid inriver survivals. In 2004, the agency estimated that about 35 percent of the inriver spring chinook made it below Bonneville Dam.

In 2001, the second-lowest flow year on record, inriver survival of spring chinook was estimated at about 28 percent.

The report said spring chinook traveled a little faster in 2006, but steelhead were really on a tear, especially earlier in the season. However, the travel time of spring chinook from Lower Granite to McNary Dam decreased in early to mid-April without corresponding changes in flow, while steelhead travel times did not go down during that period.

But the higher survivals for inriver migrants doesn't necessarily mean that more fish will come back as adults. Last July, NMFS researcher Bill Muir told the Northwest Power and Conservation Council that there was no statistical relationship between juvenile survival rates and adult return rates.

However, those return rates are likely to improve again next year, given the extremely high jack counts at dams this spring. Optimists say the Columbia could see a spring run of more than 300,000 chinook next year, with about 150,000 of those fish heading all the way up to Idaho past the lower Snake dams, where only about 19,000 have been counted this year. In 2001, 172,000 spring chinook were counted at Lower Granite Dam.

NMFS researcher Ed Casillas told NW Fishletter that ocean conditions off the mouth of the Columbia look good this year, with the spring transition to northerly winds well in place, which helps ocean upwelling and has led to much improved nutrient production from 2005.

"So far, everything is looking green," said Casillas, referring to his agency's system for qualifying ocean conditions.

He said hundreds of smolts were counted in a May trawl survey off the coast. "It's shaping up like 1999," said Casillas, who will be back on the ocean later this month to keep track of the smolts.

In 1999, ocean conditions rebounded from an El Niño that led to much cooler waters, high plankton production and a few years of record salmon returns from 2000 to 2004, with spring chinook numbers ranging from 170,000 to 400,000 fish. This year, the region will be lucky to get 80,000 springers back to the river.

But NMFS researchers say if the signals hold, we could have back-to-back blockbuster returns in 2008 and 2009. -Bill Rudolph

The following links were mentioned in this story:

Survival Estimates for the Passage of Spring-Migrating Juvenile Salmonids through Snake and Columbia River Dams, May 2007

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