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Ecology and salmon related articles

Spring Chinook Return Prediction
Drops from 360,700 to 189,200

by CBB Staff
Columbia Basin Bulletin - May 14, 2004

The latest estimate of the 2004 return of "upriver" spring chinook salmon to the Columbia River is roughly half what was forecast in preseason, but it is still expected to be the fifth largest in recent decades.

The top five returns since 1973 have been recorded the past five years, including the largest return since record-keeping, and counts at Bonneville Dam, began in 1938.

The Technical Advisory Committee, which advises U.S. v Oregon process as well as other harvest management forums, revised its estimate of the upriver spring chinook adult return on May 7. The committee of federal, state and tribal fisheries officials now predicts 189,200 adult upriver spring chinook will return to the river mouth. That is down from a 200,000-fish estimate made May 3 and a little more than half the 360,700 prediction made this past winter.

The fish simply aren't showing up in the anticipated numbers at dams such as Bonneville, the first hurdle on the salmon's homeward journey. The upriver spring chinook are those bound for hatcheries and spawning grounds in tributaries to the mid- and upper Columbia and Snake Rivers. They include stocks listed under the Endangered Species Act -- the endangered Upper Columbia spring and threatened Snake River spring/summer "evolutionarily significant units."

"The dam counts just haven't been hanging in there," said Stuart Ellis, a Columbia River Inter-Tribal Fish Commission biologist and vice-chair of TAC. Peak counts at Bonneville this year were 12,565 on April 20 and 13,030 on April 22. But counts have dwindled considerably -- ranging from about 1,700 to 2,400 daily for the seven-day period ending May 11. Under the established accounting method the chinook passing Bonneville are counted as springers through May 31. The summer chinook tally begins June 1. The 10-year averages show that Bonneville daily counts fall below 1,000 by mid-May.

Salmon return forecasting is an imprecise science but TAC remains nonplussed as to why their preseason forecast was so far off.

"We spent some time thinking about that but haven't come up with any great ideas," Ellis said. There could have been some sort of die-off in the ocean, for example, that fisheries officials are unaware of. Or changes in the fishes' maturation rate may have somehow delayed their return. Or TAC might have just made a bad forecast, plugging in wrong variables in what is a complicated calculation.

"It is disappointing that we missed it by such a large percentage," Ellis said. It's probably due to a number of factors." The forecasting method has been fairly reliable. The preseason forecasts since 1980 have largely been within 50 percent of the actual return and in most years much closer.

The reduced run forecast would still be much better than the 10-year average upriver spring chinook return -- 130,328 adults. That average is swelled by high counts of 178,600 in 2000, the 2001 record of 416,500, a 295,100-fish return in 2002 and last year's 208,900 upriver spring chinook return. The upriver spring chinook return exceeded 100,000 only three times during the 1980s and 1990s and sunk as low as 10,200 in 1995.

The tally at Bonneville through May 10 was 139,234 adult spring chinook, well above the recent 10-year average of 109,709 through that date. The count last year through that date was 161,038 and in 2000 (when the actual return was similar to the updated 2004 prediction) the count through May 10 was 159,446 at Bonneville.

The springers are proceeding quickly upriver. The count through May 10 at McNary Dam was 76,826 compared to a 10-year average of 45,184. McNary is the fourth hydro project in the system and the last the fish reach before reaching the Columbia's confluence with the Snake.

Through May 10, 52,756 adult had reached Ice Harbor Dam, the first project the salmon pass on their way up the lower Snake River. That compares to the 10-year average of 27,787.

The chinook bound for the Upper Columbia, which include the endangered stock, have not followed the trend of greatly improved returns since the turn of the century. The count through May 10 at Priest Rapids Dam was 8,153 -- below the 10-year average count of 8,783 through May 10.

Counts of jacks -- 3-year-old chinook that return prior to maturity -- are tracking near the 10 year average. The count through May 10 at Bonneville was 3,654 compared to the 3,986 10-year average. The count through May 10, 2003, was 5,997. The jacks are a primary variable when forecasts are calculated for the following year when the bulk of their brood mates return as 4-year-olds to spawn.

"Jack counts clearly are not as high as last year," Ellis said. But he stressed it is too early to make any guesses about next year's return based on that lower count.

When it became obvious that the 2004 run would be much less abundant than anticipated, all non-tribal mainstem sport and commercial fisheries were first limited, and then shut down. The last were closed last week. It is estimated that the non-tribal catch represented a 2.5 percent "impact" on the overall upriver run. Those fisheries were managed to 2 percent impact on the upriver run. But when the run forecast plummeted that meant that the catch in hand represented higher impacts. The non-tribal harvest was 24,800 chinook.

Commercial fisheries were approved for four Columbia treaty tribes both last week and this week in the Columbia River mainstem reservoirs above Bonneville. The tribes' allowable impacts are based on a sliding scale with a higher percentage harvest allowed on more abundant runs. With the forecast almost halved, the tribes' allowable impact dropped from 13 percent to 9 percent of the upriver run.

Through last week the tribes had caught an estimated 12,171 chinook, which represents a 6.4 percent impact based on the new run-size forecast. That harvest includes 8,066 caught under spring ceremonial permits, 900 from platform fisheries and about 3,200 during last week's commercial fill net fishery.

The tribes estimate that they will catch a similar number of fish during a 3 -day commercial fishery that ends at 6 p.m. Friday, May 14.


CBB Staff
Spring Chinook Return Prediction Drops from 360,700 to 189,200
Columbia Basin Bulletin, May 14, 2004

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