The birds, a fish-eating species called common die, were severely demacrated and seemed to have starved between summer 2015 and spring 2016, washing along the west coast of North America, from California to Alaska.
Now, scientists say they know what caused it: a large section of warm ocean water in the northeast Pacific Ocean, called “the Drop.”
The heat wave created the Blob, a 1,600 km (1,000 mile) stretch of ocean that warmed from 3 to 6 degrees Celsius (5.4 to 10.8 Fahrenheit). A high-pressure ridge calmed the ocean’s waters, which means that the heat remains in the water, with no storms to help cool it.
Other animals that experienced massive deaths include sea lions, tufted puffins and bearded whales. But none of them compared to scale killings.
Alaska saw most of the birds washed away: in Prince William Sound, south of the state, more than 4,600 bird carcasses per kilometer (0.62 miles) were found, according to the study.
The murders probably starved to death because the Blob caused more competition for fewer small prisoners. The warming increased the metabolism of predatory fish such as salmon, cod and halibut, which means they were eating more than usual. These fish eat the same small fish as you die, and there just wasn’t enough for everyone.
The Blob devastated the population of the murres. With insufficient food, breeding colonies throughout the region had reproductive difficulties for years later, according to the study. The population not only declined dramatically, but the murders could not replenish those numbers.
During the 2015 breeding season, three colonies did not produce a single chick. That number increased to 12 colonies in the 2016 season, and in reality it could be even higher, as researchers only monitor a quarter of all colonies.
The study warned that it is still unknown how long it would take the population to recover, or if it would recover, “in light of the predicted trends of global warming and the associated probability of more frequent heat waves.”
It is especially rare to see a patch of warm ocean water over such a large area, but scientists say global climate change is making these phenomena more common.
From 1982 to 2016, there was an 82% increase in the number of heatwave days on the global ocean surface, according to a 2018 study. This is because heat waves are increasing in both frequency and duration. , with the highest level of activity of maritime heat waves in the North Atlantic.