the film forum library tutorial contact

Mystery of the Missing Chinook by Allen Thomas, Staff Writer The Columbian, January 5, 2006

A combination of factors appear responsible for Columbia River spring chinook runs falling far short of the forecast in the past two years, the most important being worsening ocean survival conditions. State, federal and tribal biologists completed a review in November why the Columbia's spring chinook returns were so far below predictions in 2004 and 2005.

Each December, the states make a forecast of how many spring chinook are expected to enter the river from February through mid-June destined for waters upstream of Bonneville Dam.

The forecast is an important number. Harvest rates allowed under the federal Endangered Species Act for sport and commercial fishermen in the lower Columbia are based on the forecast.

But in 2004 and 2005, the model used to forecast the spring chinook run went badly awry. In 2004, the forecast was for a run of 360,700, while the actual return was 193,400, just 54 percent of the prediction.

In 2005, the forecasting model missed even worse. The prediction was 254,100, compared to an actual return of 105,000, only 41 percent of what was expected.

Curt Melcher of the Oregon Department of Fish and Wildlife said, historically, the model has performed well, usually coming within 20 percent of the actual spring chinook return.

"In 2004 and 2005, for whatever reason, the predictor model performed very poorly,'' Melcher said. "We're all struggling with that.''

The biologists looked at a variety of factors and determined the following:

• Tributary rearing survival -- Streamflows may have been worse in 2002 and 2003, the years these fish would have been rearing in freshwater, than in 2000 and 2001.

  But, if young fish died due to low flows, this should have been demonstrated in low jack returns as well as low adult returns. The relatively high jack return and lower adult returns are not consistent with this theory.

• Juvenile passage survival -- The estimated survival of young fish migrating down the Snake and Columbia rivers in 2002 was similar to levels observed prior to 2001. In 2003, survival was believed to be lower than average in the Snake, but average between McNary and Bonneville dams in the Columbia.

  "It appears that while migration conditions were not excellent in either year, they were not out of the range of typical,'' according to the report.

  If the survival through the dams was worse than average in 2002 and 2003, the jack return should have indicated this, but did not.

• Canadian/ocean fisheries -- Coded wire tags placed in the snout of Columbia spring chinook show up at very low levels in ocean fisheries.

  Although the Makah tribal winter troll fishery in the Strait of Juan de Fuca in late 2004 and early 2005 greatly exceeded chinook catch expectations, no coded wire tags from upper Columbia spring chinook were sampled.

  Even though the catch of Columbia River spring chinook was somewhat higher in the troll fishery off the west coast of Vancouver Island, it was still relatively small.

  "The harvest in the WCVI fishery does not account for the difference between the forecast and actual run size in 2005,'' the report states.

• Marine mammal predation -- The report includes some interesting numbers on spring chinook, California sea lions and harbor seals.

  Populations of marine mammals have tripled since 1970. There are 3,000 seals and 300 to 500 sea lions in the Columbia in winter and spring. They follow the smelt and spring chinook into the Columbia in winter and tend to leave the river in early June.

  Monitoring by the U.S. Army Corps of Engineers at Bonneville Dam found sea lions and seals were present more than 100 days in 2005. They ate more than 2,900 salmon and steelhead, or 3.4 percent of the run.

  In the past four years, marine mammal predation at the dam has jumped from 0.4 percent of the run to 3.4 percent.

  These numbers only reflect what's happening between Tanner Creek and the dam. There are no reliable estimates for spring predation in the rest of the river.

  Sampling in 2005 also found 22 percent of the spring chinook at Bonneville showed a bite, scrape or claw mark from a marine mammal, an increase of 83 percent over 2004.

  Seals and sea lions always have been in the lower Columbia feeding on spring salmon. There's lots of evidence the number of marine mammals is increasing, along with their predation.

  But marine mamals alone are not the cause of the forecasts being too high.

  "...the estimted predation in the Bonneville tailrace only accounts for a small fraction of the missing fish in either 2004 or 2005,'' the report states.

• Ocean conditions -- The biologists are not even sure where the bulk of any particular spring chinook stock is in the ocean at any given time because coded wire tag recoveries are so few.

  Ocean conditions for salmon appeared to be on the decline in 2004 and 2005.

  There was a lack of upwelling, which brings colder nutrient-rich water to the surface and stimulates the food chain. Temperature conditions also were not favorable.

  Spring chinook headed for the Willamette, Klamath, Rogue rivers did not return as predicted. Spring and summer chinook returns to the Fraser River were near record lows.

• Conclusion -- The committee of scientists "has not been able to make a definitive conclusion regarding why there was such a significant difference between the pre-season forecast and the actual spring chinook return,'' the report states. "TAC (technical advisory committee) believes that the reason is most likely due to a combination of factors working together. ... The available data suggests that no single source (i.e. Canadian fisheries or sea lions) can be blamed alone. TAC believes that the most important factor may be an adverse change in marine conditions.''