In addition, hatchery operators in the Snake River Basin also imported eggs from many other stocks outside the Snake River Basin, including the Carson, Klickitat, Cowlitz, Leavenworth, Marion Forks and South Santiam stocks from west of the Cascade Mountains. Thus many Snake River spring chinook now protected as endangered on account of their valuable genetic structure are in fact mongrels. State and tribal hatchery operators would use sperm from one captured male to fertilize eggs from literally dozens of females. In nature, the practice is just the opposite, where more than one male frequently fertilizes the eggs of a single female. 28 Culls from the hatchery tanks, often unfit or diseased, were released to the streams.
Many biologists believe that the disease was transferred from hatchery to wild stocks.
Juvenile salmon with BKD may have significantly lower survival rates, dying salmon slowly over a period of one to three months. While Raymond speculated that dam passage exacerbated the effects of BKD, no one has any solid documentation of such an effect. After nearly two decades, fishery managers have finally learned how to control BKD, pasteurizing the ground-up fish they served to juveniles in the tanks. Anecdotal accounts suggest that by the mid-1990s, outbreaks of the disease are less prevalent. Unless and until salmon populations evolve resistance to BKD, losses from BKD may continue to bar the achievement of historic return rates.