In 2020, participants of the UW-led Coastal Observation and Seabird Survey Team, or COASST, and other observers first identified the massive mortality event affecting common murres along the West Coast and Alaska. That study documented 62,000 carcasses, mostly in Alaska, in one year. In some places, beachings were more than 1,000 times normal rates. But the 2020 study did not estimate the total size of the die-off after the 2014-16 marine heat wave known as "the blob." "This study shows clear and surprisingly long-lasting impacts of a marine heat wave on a top marine predator species," said Julia Parrish, a UW professor of aquatic and fishery sciences and of biology, who was a co-author on both the 2020 paper and the new study. "Importantly, the effect of the heat wave wasn't via thermal stress on the birds, but rather shifts in the food web leaving murres suddenly and fatally without enough food."
Before this marine heat wave, about a quarter of the world's population, or about 8 million common murres, lived in Alaska. Authors estimate the population is now about half that size. While common murre populations have fluctuated before, the authors note the Alaska population has not recovered from this event like it did after previous, smaller die-offs. While the "warm blob" appears to have been the most intense marine heat wave yet, persistent, warm conditions are becoming more common under climate change. A 2023 study led by the UW, including many of the same authors, showed that a 1 degree Celsius increase in sea surface temperature for more than six months results in multiple seabird mass mortality events.
We may now be at a tipping point of ecosystem rearrangement where recovery back to pre-die-off abundance is not possible. Other co-authors are Brie Drummond and Jared Laufenberg at the U.S. Fish and Wildlife Service offices in Alaska; John Piatt, a former federal scientist now with the World Puffin Congress in Port Townsend; and Martin Renner at Tern Again Consulting in Homer.