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Low 2005 Run Still Mystifies Scientists

by Henry Miller
Statesman Journal, January 31, 2006

Young Salmon Calculations, Ocean Issues May be Causes

OREGON CITY -- The ocean did it.

At least as far as scientific sleuthing has been able to determine, that's the cause of the underwhelming run of Columbia River spring-run chinook salmon in 2005, despite preseason indications of a banner year.

Biologists in Oregon and Washington had forecast a run of more than a quarter million fish, 254,100.

A total of 106,900 showed up in the Columbia and its tributaries.

"Basically, we looked at a number of different likely culprits that various folks think might be responsible for this shortfall," said Stuart Ellis.

Ellis is a fisheries scientist for the Columbia River Inter-Tribal Fish Commission.

He's also the chairman of the Technical Advisory Committee (TAC), which makes the forecasts, and looked long and hard at the evidence to try to come up with an answer to what went wrong the past year.

"We included everything from the hydropower system to losses in the tributaries to sea lions to ocean fisheries to the actual numbers in the harvest themselves," he said.

Ellis' report was directed at the Oregon and Washington representatives of the Columbia River Compact during a meeting the past week.

The scientists didn't come up with a smoking gun.

But there were the scientific equivalent of traces of powder burns, Ellis said about the results. "It may not be a very satisfying report to some folks, although the TAC seems satisfied with it," he said. "Our determination was that we didn't think that there was any single factor that was predominantly responsible for the shortfall."

Instead, it was more likely a combination of factors, the two greatest of which were the method of predicting runs based on the number of immature, small salmon called jacks that showed up in 2004, and a souring of ocean conditions.

"We take data of jacks and older-age fish and develop mathematical relationships between these fish that we use to predict the number of fish by age," Ellis said. "And in 2004, we actually saw a relatively strong return of jacks, which is the single biggest driving factor in any of our forecasts."

The ocean apparently sabotaged the rosy predictions those jack numbers spun.

"Then there's ocean survival," Ellis said. "That is a very likely an explanatory factor in how come you can have a relatively good return of jacks and suddenly the adults don't materialize out of that."

Spring-run chinook are the most balky to predict among salmon runs, Ellis added. That's because it is a mix of genetic stocks returning to the Snake, Willamette and Columbia rivers and tributaries with both native wild fish and hatchery salmon thrown into the already dizzying mix.

"With our spring chinook forecast, we're forecasting a very large and diverse group of fish, unlike some of our other forecasts, which are more stock-specific," Ellis said. It's a little bit harder to do ... and there is some inherent uncertainty in the forecast."

But that cuts both ways, because diversity in the runs is one of the factors that points to the change in ocean conditions at the primary reason the 2005 runs tanked, said Curt Melcher.

Melcher is the assistant Fish Division administrator for the Oregon Department of Fish and Wildlife and the state's representative to the compact.

At first blush, looking at the huge declines in both upriver Columbia and Willamette stocks in 2005, "you think you have somewhat of an 'oh, there's an aha!' " Melcher said about the overall shortfall.

But when you pick apart each run, the decline on the Willamette was pegged to the failure of the forecast strong return of 5-year-old salmon.

While on the Columbia, it was the 4-year-old fish that didn't show.

Now you get your aha moment, Melcher said: The ocean must be the cause.

"So different brood years," Melcher said. "They were subjected to different conditions in the rivers (before the fish went to sea). There's clearly something going on in the ocean with regard to the maturation schedule, I believe." Ellis said this year's prediction of 88,400 spring chinook is based on a tweaked formula that scientist believe will be more accurate.

"We did make some relatively minor adjustments in how we are treating jacks that we think may prove to be a more realistic method under the circumstances that we looked at," he said. "And I think in general TAC felt fairly confident that this year's forecast is a reasonable forecast."

With the qualifier that they're still working with the least predictable run of salmon, Ellis added.

Henry Miller
Low 2005 Run Still Mystifies Scientists
Statesman Journal, January 31, 2006

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