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NW Fishletter #257, February 9, 2009

[1] Feds Say Big Sockeye Returns Had Little To Do With Spill

Last year's sockeye run on the Columbia River--230,000 were counted at Bonneville Dam, making it the largest return since 1959--was the result of factors outside of the hydro system, according to a new study by NOAA Fisheries. They said the good return on the Snake--the highest since the early 1970's--was likely due to factors outside the basin as well.

The feds' latest analysis flies in the face of a Fish Passage Center analysis last summer that found good inriver conditions like increased spill at lower Snake dams in 2006, were likely the reasons for the 800 or so ESA-listed sockeye making it back to Idaho in 2008.

A preliminary federal analysis responded to the FPC last July 24. Then the FPC released a review of the feds' analysis on Aug. 6, which echoed their position that inriver conditions, not ocean conditions, were responsible for the big numbers in 2006.

The feds' Feb. 6 memo from the Northwest Fisheries Science Center in Seattle said the sockeye return rates from 1996 to 2008 correlated weakly with the ocean indicators developed by the agency, but they also noted that those indicators didn't include the food resources important for young sockeye.

They also found a strong correlation between estimated return rates of the Upper Columbia and Snake stocks, which suggests that changes in ocean productivity led to the big returns last year.

In addition, the scientists found no correlation between sockeye salmon SARs [smolt-to-adult return rates] and indices of mainstem flow and percentage spill at dams between McNary and Bonneville.

"This suggests that the primary factors influencing the variation in annual adult returns acted downstream from Bonneville Dam, and on both stocks in common," said the memo.

In fact, the feds said the return rates to the Upper Columbia, where most of last year's 230,000 sockeye were bound, showed a "significant negative relationship" with increased spill rates between Rock Island and McNary dams.

"This finding is in opposition to a large body of information indicating that increased spill at dams, within limits, improves the survival of juvenile steelhead and chinook migrating during spring (e.g. Muir et al 2001; Ferguson et al. 2005). It merits a more detailed review and analysis of specific project operations and passage conditions."

The study found a positive correlation between spill at lower Snake dams and estimated juvenile survival, "but the correlation was not significant."

Nor did the feds find a significant relationship between juvenile survival and flow, percentage spill or water temperature in the rest of the mainstem Columbia.

Most of the sockeye from the Snake were transported in recent years, but so few returned that agency scientists could not determine whether barging helped or hindered the Snake run, which has been kept going by an expensive captive broodstock program.

The feds said last year's good return to Idaho's Redfish Lake was partly due to increased smolt production in 2006.

They also said ocean harvest regimes had not changed much, so that wasn't a factor, either.

Cooler water conditions for returning adults also helped last year's return to Idaho, they said, when more than 75 percent of the adults counted at Lower Granite dam made it the last 450 miles of their migration to the Stanley Basin. In some recent years, less than 10 percent have made it.

The feds said that SARs for the Upper Columbia sockeye were generally a lot higher because migration distances were shorter, and most of the fish were of wild origin.

They estimated that Upper-C sockeye SARs in recent years have ranged from 0.67 percent to 8 percent, while Snake sockeye SARs varied from 0.07 percent to 0.7 percent. -Bill Rudolph

The following links were mentioned in this story:

Fish Passage Center, July 14, 2008 Memorandum

NW Fishletter Issue 250

Fish Passage Center, July 21, 2008 Memorandum

Fish Passage Center, August 6, 2008 Memorandum

Factors affecting sockeye salmon returns to the Columbia River in 2008

Ocean Ecosystem Indicators of Salmon Marine Survival in the Northern California Current

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