About 1 million common murres died during a 2015-16 heat wave, scientists have said. Researchers believe that a disrupted food supply led to the mass die-off of the North Pacific seabirds.
Approximately 1 million seabirds known as the common murre died because of food-supply disruptions during a heat wave from summer 2015 to spring 2016, according to a study published Wednesday in PLOS One. Julia Parrish, a University of Washington ecologist and co-author of the paper, linked the "relatively new" increased frequency of such heat waves to climate change.
The study called the number of birds — many of breeding age — killed over a geographic area the size of Canada "unprecedented and astonishing." According to researchers, "the most powerful marine heat wave on record," which ran from 2014 to 2016, created a mass of seawater known as "the Blob." That coincided with the warmed Pacific of an El Nino period.
About 62,000 emaciated murres washed ashore dead or dying along the North American Pacific coastline during the heat wave. Scientists estimate the total deaths at between 500,000 and 1.2 million.
'Very different environment'
Parrish said the heat wave had a twofold effect. First, elevated temperatures reduced the quality and quantity of phytoplankton, reducing the quantity and quality of herring, sardines and anchovies: fish eaten by common murres, which measure 1 foot (30 centimeters), fly fast and can hunt 650 feet below the water's surface. Second, warming waters meant that salmon and Pacific cod, which compete with the murres, needed to eat more.
The murres' need to consume half of their body mass every day has become their evolutionary "Achilles heel" as the climate changes, John Piatt, a research biologist at the US Geological Survey's Alaska Science Center and the paper's lead author, told the AFP news agency. "Everything they do depends on that breast muscle," he said. "When they can't eat three or four days, they burn up all that muscle" — and can no longer fly or dive.
Murre colonies across the entire region failed to produce chicks for years during and after the heat wave event, the study found. Several other species experienced mass die-offs during the same period, including tufted puffins, Cassin's auklets, sea lions and baleen whales. But, by all metrics, including overall number and geographic extent, the common murres experienced by far the largest die-off.
Taken together, the mass deaths demonstrate that "a warmer ocean world is a very different environment and a very different coastal ecosystem for many marine species," Parrish said, calling seabirds, as highly visible members of that system, "bellwethers of that change."
mkg/sms (AFP, PLOS One)