Do Ocean Conditions Trump Dam Effects?  

Northwest Fishletter

September 20, 2007

Regional salmon scientists briefed members of the Northwest Power and Conservation Council last week on some of their latest findings at a two-day confab in Portland designed to improve the dialog between researchers and policymakers. Members heard reports on various aspects of habitat restoration, mainstem survival, along with estuary and ocean research.

With BPA poised to spend more than a billion dollars on dam improvements and habitat projects in the Columbia Basin that double as jobs programs, some federal scientists were pointing more than ever to the ocean's huge role at determining the numbers of returning salmon.

But our knowledge of ocean processes is pretty skimpy compared to the huge amounts of information gleaned about salmon before they leave their rivers. University of Washington oceangoing scientist Kate Meyers pointed out that 99 percent of the research on salmon deals with its life in fresh water, while 99 percent of its growth occurs in salt water.

NMFS scientists were on hand to repeat what they have found in recent years--that juvenile salmon survival down the Columbia and Snake rivers doesn't correlate very much with their returning adult numbers. NOAA Fisheries researcher John Williams, from the agency's Seattle-based science center, even questioned the value of developing juvenile survival goals for juvenile passage through the hydro system.

Fellow federal scientist Steve Smith pointed out to the freshwater-centric crowd that most of the fish die in the ocean, not the river.

"There's a much larger amount of mortality happening in the ocean," said Smith, who countered an argument raised by US Fish and Wildlife staffer Howard Schaller. Schaller claimed spring chinook stocks from the Snake River die off at higher rates than stocks downriver like the John Day because they pass more dams before they enter the ocean.

Schaller called it "differential mortality," and when pressed about policy implications, he said dam operators needed to get fish through the hydro system faster--which would happen with higher flows.

However, NMFS scientist Bill Muir reported that his agency has estimated that direct survival of this year's inriver spring chinook migration was about 56 percent, nearly as high as last year's 61 percent, when flows were significantly higher, and steelhead survivals were about 37 percent. Last year, they were 42 percent. Muir said that 2007's numbers are considerably higher than the similar low-flow, high temperature year of 2004.

Muir also reported that survival studies with wild PIT-tagged fish showed 60 percent less smolt-to-adult return rates than the run at large and similar trends for PIT-tagged hatchery chinook, which showed 40 percent to 50 percent lower SARs than for hatchery fish at large.

Further, Muir said their research showed no real correlation between SARs and inriver survival of juvenile migrants.

Schaller agreed, and tried to explain his analysis that was recently published in a fisheries journal, that purports to show evidence that mortality of the Snake stocks was higher than downriver runs like the John Day once the fish were beyond Bonneville Dam.

What Schaller didn't mention was that his analysis had been one of seven different hypotheses analyzed last winter by an independent panel of scientists (Independent Scientific Advisory Board) who concluded that Schaller's attempts (along with co-author Charlie Petrosky of IDFW) to quantify the "latent mortality" was basically a waste of time, and scientists should spend their time more wisely by determining the biological benefits of transporting fish downstream in barges.

Schaller said that 71 percent of the variation in Snake spring chinook SARs could be explained by three variables, water travel time, the Pacific Decadal Oscillation index and coastal upwelling.

But NMFS scientist Williams and co-author Mark Scheuerell published a 2005 paper that said 71 percent of the variation in the Snake spring chinook SARs could be explained by coastal upwelling alone, and they generated an even higher correlation (r² = .96) when they used another form of the dynamic time-series model that used all the available data.

Confused? The ISAB is now reviewing the Fish Passage Center's 10-year retrospective survival study, which supports Schaller's hypothesis. Power Council chair Tom Karier told NW Fishletter he is waiting for its review before he makes up his mind about the matter. He did mention what others had said at the meeting--that higher inriver flows may be related to La Nina years, when there is more precipitation, oceans are cold and upwelling brings up significant nutrients from the deep to kick-start ocean productivity.

Karier said the meeting raised some significant questions about carrying capacity--how much can we add to stocks by improving conditions in upriver habitat, and the estuary, where a recent acoustic tag study has estimated that about a third of all smolts perish between Bonneville Dam and the ocean. Or how much can we expect from the ocean when offshore conditions are poor and flooded with hatchery releases?

He sees a role for the Council to help direct research in the most important areas. "You can't just leave it up to the science people or policymakers," said Karier, who noted that the best way to set priorities would be a process that used both sides for input.

Karier said he was especially concerned about the report that important fall chinook transport studies may have to be postponed again in 2008 because not enough young fish will be available because of other production priorities in the US v. Oregon process. He said the Council could help by getting parties together put those studies back on course, even if it means shifting funding to get the work done.

NOAA Fisheries scientists also reported on their latest modeling results, which showed that each dam and reservoir accounted for about 10 percent of juvenile mortality, with about half occuring at each dam, and the other half in the accompanying river reach

The following links were mentioned in this story:

Howard A. Schaller and Charles E. Petrosky, Assessing Hydrosystem Influence on Delayed Mortality of Snake River Stream-Type Chinook Salmon, North American Journal of Fisheries Management, Volume 27:810-824

Mark D. Scheuerell, John G. Williams, Forecasting climate-induced changes in the survival of Snake River spring/summer Chinook salmon, Fisheries Oceanography, Volume 14 Issue 6 Page 448-457

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