|Document Type:||Journal Article|
|Title:||Potential impacts of Renibacterium salmoninarum on adult returns of Snake River spring-summer chinook salmon|
|Author:||John G. Williams|
|Journal:||Bulletin of National Research Institute of Aquaculture|
Snake River spring/summer Chinook salmon populations declined rapidly during the mid- to late 1970s after construction of four lower Snake River dams. Considerable efforts followed to improve the direct survival of downstream-migrating juvenile smolts through these four dams, and through four additional dams on the lower Columbia River. Presently, although survival of downstream migrants is now as high or higher than it was prior to construction of the Snake River dams, adult return rates remain low. Therefore, other factors that have increased mortality compared to pre-dam conditions must act on the fish in the lower Columbia River estuary or in the ocean. One hypothesis is that Renibacterium salmoninarum, a bacterium found in nearly all Snake River Chinook salmon and the causative agent of bacterial kidney disease (BKD), is responsible for decreased adult returns. This hypothesis assumes that the disease is triggered by stress associated with bypass systems at dams or during the smolt transportation process. In a related hypothesis, hatchery fish with high levels of R. salmoninarum intermingle with wild fish and spread infections, which result in increased mortality. A final hypothesis is that decreased ocean productivity may account for the low Chinook salmon returns.