Spring Chinook Run is Strongby US Army Corps of Engineers,
Newsletter Walla Walla District, July, 2000
The region received some encouraging news regarding wild spring chinook salmon, which is one of the four lower Snake River anadromous fish species listed under the Endangered Species Act. The number of wild and hatchery spring chinook salmon passing Bonneville Dam on their way upstream this year was the highest since counts began in 1938.
How Do This Year's Counts Compare
This year's adult spring chinook run was 4.6 times greater than the 1999 run and 2.9 times greater than the 10-year average. Counts at Bonneville Dam show that 199,595 adults have passed the dam as of May 31.
Early counts of adult summer chinook at Bonneville suggest that the strong run will continue. Based on counts from the first two weeks of June, this year's adult summer run (which officially began on June 1), is 3.8 times greater than the 1999 run and 2.6 times greater than the 10-year average.
The fish passge count at Bonneville Dam is not a perfect measure of run strength because it occurs after a portion of the fish are taken through ocean harvest and lower river harvest, but it does provide a good basis for comparison. For instance, although this year's count is higher than in 1972 when 186,000 fish passed the dam, it is likely that many more fish actually returned to the mouth of the Columbia that year. Harvest was not as restricted then as it is now, so more fish were removed from the ocean and lower river before they could be counted at Bonneville. To put this year's encouraging returns in historical perspective, it is estimated that the Snake River Basin produced about 1.4 million chinook salmon prior to the arrival of Euro-Americans (Northwest Power Planning Council, 1986)
Generally 80 to 90 percent of the returning fish are hatchery produced. Later this summer, scientists will survey tributaries to count redds (nests) and perform other analyses to determine how many fish were wild.
How Do Returns Look in the Near Future?
This year's strong jack run indicates that the upward trend in adult spring-summer chinook returns may continue in 2001 and 2002. "Jacks" are spring-summer chinook that return as 2 or 3 year olds, after spending only 1 year of their life in the ocean. Chinook salmon usually spend 2 to 3 years in the ocean before returning to spawn at 4 to 5 years old. Jack counts are often an indicator of the magnitude of following years' returns. This year's spring chinook jack run of more than 21,000 fish was almost 8 times greater than the 10-year average.
What Has Caused the Higher Returns?
The fish counts and relatd data on habitat conditions and other factors are preliminary and have not been fully analyzed, so it is difficult to determine what has caused the resurgence. However, it it possible to speculate that improvements in ocean conditions over past years in turn improved the survival prospects of spring chinook. Another factor could be that the returning adults experienced strong spring flows during 1996 and 1997 when they were migrating to the ocean as juveniles. That eased down-river passage and may have improved their survival chances. A recent U.S. Canada fishing agreement that has limited ocean harvest of these fish, and improvements in dam passage technology could also be contributing to the increased spring chinook returns.
What Do the Improved Counts Mean for the FR/EIS?
While they are encouraging, these new data are raw and have not been thoroughly studied. Regional scientists wil examine the possible factors that could have contributed to the increase returns, and the confirmed data and scientific analysis will be considered as part of the ongoing FR/EIS>
Fish Passage Center
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