Before the two-year marine heat wave that ended in 2016, Alaska had an estimated 8 million common murres — a quarter of the world’s population — spread across abundant colonies in the Gulf of Alaska and the Eastern Bering Sea. These black-and-white seabirds nest in dense clusters among shoreline cliffs during the summer months and then head to the ocean the rest of the year to feast on schools of small fish such as capelin and sand lance, herring and krill.
Some populations of such forage fish collapsed during the heat wave as temperatures in the north Pacific spiked by 2.5 to 3˚C above normal. Many predators that rely on them suffered. The number of Pacific cod in the Gulf of Alaska crashed by 80%. The number of humpback whales in the north Pacific fell by 20%. Other species from chum salmon to snow crabs also plummeted.
A study compared a seven-year period (2008-2014) before the marine heat wave and another seven-year stretch afterwards (2016-2022) and found that murre numbers fell 52 to 78% at 13 colonies across two large marine ecosystems in the Bering Sea and the Gulf of Alaska. And since that die-off, the common murre population has remained down, showing no signs of recovery.
The research by Renner and her colleagues found that more than half of Alaska’s common murres died — some 4 million birds — in what they described as the largest mortality event of any non-fish vertebrate wildlife species reported during the modern era. The killing was an order of magnitude larger, she said, than the hundreds of thousands of murres that perished in the 1989 Exxon Valdez oil spill in Alaska.