When Good Fish Make Bad Decisions: Coho Salmon in an Ecological Trap

Abstract

AbstractCoho salmon Oncorhynchus kisutch are a threatened species in California. In the Shasta River, they may be caught in an ecological trap that is exacerbating their decline. Adults appear to have equal preferences for spawning habitat that reduces the survival of their young and that of apparently similar quality where survival would be more likely. The primary cause of juvenile mortality is water withdrawals, which degrade summer water quality and create barriers to movement to habitats with more suitable rearing conditions. The situation has been exacerbated by the addition of gravel to support spawning fall‐run Chinook salmon O. tshawytscha, creating habitat that is also attractive to spawning coho salmon in locations where juvenile coho salmon survival will be extremely low. The Shasta River acts as a conceptual model of how habitat degradation and ecologically naive restoration actions may combine to create severe ecological traps for nontarget species.Received March 10, 2011; accepted October 11, 2011