Decline in Salmon Size Signals Potentially Significant Fisheries and Ecosystem Shift in the North Atlantic

Science Advances, 4 March 2022

In 2005, a sudden reduction in the transport of Arctic water into the Norwegian Sea resulted in widespread changes throughout the Northeast Atlantic ecosystem. The resulting rush of warm water into the Norwegian Sea elevated spring water temperatures, coinciding with a 50% reduction in zooplankton abundance across large areas of the Northeast Atlantic Ocean. At the same time, Atlantic salmon caught in Norwegian rivers abruptly decreased in body size and began spending more time out at sea each season. These changes in salmon growth and behavior suggest that their food availability decreased, at the same time as the longer period at sea increased their vulnerability to predators. Within the next two years, mackerel growth collapsed in a similar manner. These simultaneous changes in water temperature, zooplankton availability, and salmon and mackerel growth point toward an ecosystem-scale regime shift in the Northeast Atlantic. Similar declines were observed in France and Scotland, suggesting that large geographic areas were impacted. This study underscores that even small changes in temperature can have disproportionate and cascading long-term effects on wildlife, food webs, and ecosystems.