A new study written by several fisheries experts discusses the pratfalls that are affecting North Pacific sockeye salmon. Among the authors of the study was Dr. Greg Ruggerone, a longtime Alaska salmon guru who was part of pink salmon/sockeye research that we featured in 2018.
Here’s the latest paper’s overview, which focuses on warming ocean waters and the abundance of hatchery fish that are creating crowded waters.
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.
Here’s what Ruggerone told the National Center for Ecological Analysis and Synthesis:
And the consequences of increasing abundances of wild and hatchery pink salmon across the North Pacific may be felt by more than just other salmon. “Our work contributes to a growing body of evidence that increasing abundances of salmon across the North Pacific, and in particular pink salmon, are linked to a trophic cascade resulting in fewer zooplankton, reduced growth, survival and delayed maturation of salmon and other marine fishes, reduced reproductive success of seabirds, and perhaps even reduced foraging efficiency of southern resident killer whales” says Dr. Greg Ruggerone Vice President of Natural Resources Consultants and co-author on the study.