On the one side, the murre's preferred prey species, fish like anchovies, juvenile salmon, capelin and sardines, are ectothermic or cold-blooded. "No other factor was found that could explain the magnitude or spatial extent of these events", Piatt said.
There have been several other marine heat waves emerging in recent months.
The study-which its authors expect to inform research on other mortality events related to marine heatwaves-was published just weeks after University of Washington scientists found what some have called "the blob 2.0" forming in the Pacific.
"We narrate that the smoking gun for basic murres - beyond the marine warmth wave itself - used to be an ecosystem squeeze: fewer forage fish and smaller prey in basic, at the similar time that opponents from colossal fish predators take care of walleye, pollock and Pacific cod enormously increased", said gaze co-creator Julia Parrish, a University of Washington professor within the College of Aquatic and Fishery Sciences.
A new study suggested that between 2015 and 2016 nearly around a million of common murres was forced to starve. Sure enough, while dead murres were washing ashore in droves, adult Pacific cod populations in the Gulf of Alaska were "silently crashing" below the surface, Piatt said. This particular one was exacerbated with warming winds from El Niño during 2015 and 2016. The die-off eventually killed an estimated 500,000 to 1 million murres from California to Alaska, eliminating 10-20% of the northeast Pacific population of the species.
Given that previous studies have shown "that only a fraction of birds that die at sea typically wash ashore", the researchers put the death toll closer to a million.
Alaska saw the most birds wash up. Murre breeding colonies across the entire region failed to produce chicks for years during and after the heat wave event, the study found.
To better understand this anomalous die-off, Piatt and colleagues analyzed data on dead and dying birds from West Coast bird rehabilitation centers, citizen science beach surveys, community reports, and studies conducted by universities, private organizations, and government entities. "It was astonishing and alarming, and a red-flag warning about the tremendous impact sustained ocean warming can have on the ecosystem".
The Blob reached 6 degrees Celsius above typical maximum temperatures in places and extended to a depth of 200 meters, and more than 3,000 kilometers up the United States coastline into Alaska. As a result, the once-plentiful schools of forage fish that murres rely on became harder to find.
"Food demands of large commercial groundfish like cod, pollock, halibut and hake were predicted to increase dramatically with the level of warming observed with the blob, and since they eat numerous same prey as murres, this competition likely compounded the food supply problem for murres, leading to mass mortality events from starvation", Piatt said. Using data from almost 5,800 beach surveys, public reports, and data from dozens of seabird rehab centers from Alaska to California, the researchers concluded the die-off was much higher.
Meanwhile, another huge heat blob has formed off the Washington coast and up into the Gulf of Alaska, and is growing.
"All of this-as with the Cassin's auklet mass mortality and the tufted puffin mass mortality-demonstrates that a warmer ocean world is a very different environment and a very different coastal ecosystem for many marine species", says Parrish, who is also the executive director of the Coastal Observation and Seabird Survey Team, known as COASST. The panel also projected that oceans will absorb two to four times more heat by the end of the century than they did in the past 50 years if global warming is limited to 3.6 degrees.