The road to extinction is paved with good intentions: negative associationof fish hatcheries with threatened salmon

Hatchery programmes for supplementing depleted populations of fish are unde rgoing a worldwide expansion and have provoked concern about their ramifica tions for populations of wild fish. In particular, Pacific salmon are artif icially propagated in enormous numbers in order to compensate for numerous human insults to their populations, yet the ecological impacts of this mass ive hatchery effort are poorly understood. Here we test the hypothesis that massive numbers of hatchery-raised chinook salmon reduce the marine surviv al of wild Snake River spring chinook, a threatened species in the USA. Bas ed on a unique 25-year time-series, we demonstrated a strong, negative rela tionship between the survival of chinook salmon and the number of hatchery fish released, particularly during years of poor ocean conditions. Our resu lts suggest that hatchery programmes that produce increasingly higher numbe rs of fish may hinder the recovery of depleted wild populations.