Story at a glance
- A blob of hot water in the Pacific Ocean ravaged food supplies for common murres between summer 2015 and spring 2016.
- About 62,000 dead or dying seabirds washed up on shores from California to Alaska.
- A yearslong marine heat wave first began in 2013 and intensified during the summer of 2015 due to a powerful El Niño, which lasted through 2016.
Researchers estimate that up to 1 million seabirds died over the Pacific Ocean in just less than 12 months in an unprecedented mass die-off that is believed to be driven by warming ocean waters.
In a study published by researchers from the University of Washington (UW) in PLOS One, scientists say about 62,000 dead or dying common murres, a seabird of the North Pacific that can dive the length of two football fields to snatch a small fish, washed ashore between summer 2015 and spring 2016 on beaches from California to Alaska.
The culprit? A large extended marine heat wave nicknamed the “Blob” that kicked off in 2013 and intensified through the summer of 2015 due to a powerful El Niño. The shift changed the makeup of plankton communities. In response, forage fish quality and quantity diminished, devastating the murres’ food supply.
But the total number of deaths is likely to be closer to 1 million since only a small fraction of birds that die at sea wash up on shore.
“The magnitude and scale of this failure has no precedent,” the study’s lead author and research biologist at the U.S. Geological Survey’s Alaska Science Center John Piatt said in a statement. “It was astonishing and alarming, and a red-flag warning about the tremendous impact sustained ocean warming can have on the marine ecosystem.”
The study notes that elevated water temperatures reduced quantity and quality of phytoplankton, which in turn reduced quantity and quality of the fish eaten by common murres. At the same time, the warmer waters increased the metabolic needs of larger fish that compete with murres for food.
“Think of it as a run on the grocery at the same time that the delivery trucks to the stores stopped coming so often,” explained one of the study’s authors, Julia Parrish, a UW professor in the School of Aquatic and Fishery Sciences. “We believe that the smoking gun for common murres — beyond the marine heat wave itself — was an ecosystem squeeze: fewer forage fish and smaller prey in general, at the same time that competition from big fish predators like walleye, pollock and Pacific cod greatly increased.”