Climate and competition influence sockeye salmon population dynamics across the Northeast Pacific Ocean

Abstract

Pacific salmon productivity is influenced by ocean conditions and interspecific interactions, yet their combined effects are poorly understood. Using data from 47 North American sockeye salmon (Oncorhynchus nerka) populations, we present evidence that the magnitude and direction of climate and competition effects vary over large spatial scales. In the south, a warm ocean and abundant salmon competitors combined to strongly reduce sockeye productivity, whereas in the north, a warm ocean substantially increased productivity and offset the negative effects of competition at sea. From 2005 to 2015, the approximately 82 million adult pink salmon (Oncorhynchus gorbuscha) produced annually from hatcheries were estimated to have reduced the productivity of southern sockeye salmon by ∼15%, on average. In contrast, for sockeye at the northwestern end of their range, the same level of hatchery production was predicted to have reduced the positive effects of a warming ocean by ∼50% (from a ∼10% to a ∼5% increase in productivity, on average). These findings reveal spatially dependent effects of climate and competition on sockeye productivity and highlight the need for international discussions about large-scale hatchery production.