Research conducted on common murres, a seabird found in Alaska, has revealed significant impacts from the 2014-16 marine heat wave known as ‘the blob.’ An analysis of 13 colonies surveyed between the years of 2008 and 2022 indicates that the population in the Gulf of Alaska plummeted by 50% post marine heat wave. In areas of the eastern Bering Sea, west of the Alaska Peninsula, the decline was even more dramatic, reaching a staggering 75%. The authors of the study report that there has been no indication of recovery as of yet.
Common murres, often likened to flying penguins due to their stout, tuxedo-like appearance, are creatures that dive and swim to catch small fish before returning to coastal cliffs or islands where they nest in large groups. Despite their robust appearance, these seabirds are highly susceptible to changes in ocean conditions.
A citizen science initiative at the University of Washington, which trains local residents to monitor local shores for dead birds, has played a vital role in a new study conducted by federal scientists that highlights the severe impact of rising ocean temperatures on common murres in Alaska.
In 2020, members of the University of Washington’s Coastal Observation and Seabird Survey Team (COASST) and other observers first noted the widespread mortality event affecting common murres along the Coasts of the U.S. and Alaska. This study recorded over 62,000 carcasses, predominantly from Alaska, in just one year, with some beaching events being over a thousand times the normal levels. However, that study did not provide a total estimate of the die-off caused by “the blob” that occurred during the 2014-16 heat wave.
A recent publication, released on December 12 in Science, features a study led by the U.S. Fish and Wildlife Service that analyzed years of surveys to assess total bird mortality and subsequent effects. The findings from the 13 colonies examined indicate that the population size in the Gulf of Alaska decreased by half following the heat wave. In contrast, the eastern Bering Sea colonies experienced a staggering 75% decline.
Heather Renner, a wildlife biologist with the U.S. Fish and Wildlife Service, spearheaded the research, estimating that approximately 4 million common murres perished in total—around 50% of the overall population. The authors state that no signs of recovery have been observed thus far.
“This research illustrates the profound and surprisingly long-lasting repercussions of a marine heat wave on a prominent marine predator species,” remarked Julia Parrish, a UW professor specializing in aquatic and fishery sciences and co-author of both the 2020 and latest studies. “Critically, the consequences of the heat wave arose not from thermal stress on the birds themselves, but from rearrangements in the food chain which left murres with insufficient food supplies, leading to starvation.”
The so-called “warm blob” refers to an unusually persistent area of warm surface water that affected the northeast Pacific from late 2014 to 2016, disrupting weather patterns and coastal ecosystems from California to Alaska. With a decline in ocean productivity, food availability dropped for top predators such as seabirds, marine mammals, and significant fish species. Analysis of the condition of murre carcasses suggested that starvation was the most likely cause of the widespread mortality as indicated in the 2020 study.
Prior to this marine heat wave, Alaska was home to about a quarter of the global common murre population, approximately 8 million individuals. Current estimates suggest the population has now been reduced to about half of that number. While common murre populations have historically varied, the authors emphasize that the Alaskan population has yet to bounce back from this incident as it did from previous, smaller die-offs.
Though the “warm blob” represented one of the most extraordinary marine heat waves on record, such warm conditions are becoming increasingly frequent as a result of climate change. A 2023 study spearheaded by the UW, which included many of the same contributors, indicated that a rise of 1 degree Celsius in sea surface temperature sustained over six months can trigger multiple mass mortality events among seabirds.
“Be it due to a heat wave, El Niño, shrinking Arctic sea ice, or other contributing factors, the conclusion is evident: Warmer waters lead to significant shifts in ecosystems and widespread effects on seabird populations,” Parrish stated.
“The rise in the frequency and severity of seabird mortality events corresponds closely with increasing ocean temperatures,” Parrish added.
The 2023 research suggested that seabird populations typically require a minimum of three years to recover following a marine heat wave. Given that common murres in Alaska have not returned to normal levels even seven years after “the blob,” this situation raises serious concerns, according to Parrish.
“We may have reached a critical juncture in ecosystem rearrangement where returning to pre-die-off population levels may no longer be feasible.”
Additional co-authors of the study include Brie Drummond and Jared Laufenberg from the U.S. Fish and Wildlife Service in Alaska; John Piatt, a former federal scientist now affiliated with the World Puffin Congress in Port Townsend; and Martin Renner from Tern Again Consulting based in Homer.
