Survey reveals that mass die-off of seabirds due to Pacific heat wave is in full swing

A common seabird, the murre looks a little like a flying penguin. These rugged, tuxedo-style birds dive or swim in the ocean to feed on small fish, then fly back to islands and coastal cliffs, where they establish large colonies. However, their sturdy physique hides how vulnerable these birds are to changing ocean conditions.

A University of Washington citizen science program that trains coastal residents to search local beaches and record bird carcasses contributes to a new study led by federal scientists that suggests rising water temperatures may be affecting Alaska’s murres. The devastating effects were recorded.

In 2020, participants and other observers from the Washington State-led Coastal Observation and Seabird Survey Team (COASST) identified for the first time a large-scale mortality event affecting murres along the West Coast and Alaska. The study recorded 62,000 carcasses in one year, mostly in Alaska. In some places, beach fees were more than 1,000 times the normal price. However, the 2020 study did not estimate the total scale of deaths following the 2014-16 marine heatwave, known as the “blob.”

In the new paper, published Dec. 12 in the journal Science, a team led by the U.S. Fish and Wildlife Service analyzed years of colony-based studies to estimate total mortality and subsequent impacts. An analysis of 13 colonies studied between 2008 and 2022 found that the size of colonies in the Gulf of Alaska, east of the Alaska Peninsula, decreased by half after a marine heatwave. On the west side of the peninsula and along the eastern Bering Sea, the decline was even steeper, with 75% lost.

A study led by U.S. Fish and Wildlife Service wildlife biologist Heather Renner estimates that a total of 4 million Alaskan murres, or about half of the total population, have died. No recovery has yet been seen, the authors write.

“This study clearly shows that the effects of marine heatwaves on top marine predator species are surprisingly long-lasting,” said University of California Professor of Fisheries and Fisheries and Biology, 2020 said Julia Parrish, co-author of the paper. Papers and new research. “Importantly, the effects of the heat wave were not due to heat stress on the birds, but rather due to changes in the food chain, which suddenly left the murres without enough food, which became fatal.”

This “warm blob” was a prolonged period of unusually warm surface water in the Northeast Pacific Ocean from late 2014 to 2016, impacting weather and coastal marine ecosystems from California to Alaska. Reduced ocean productivity has affected food supplies for top predators such as seabirds, marine mammals, and commercially important fish. The authors of the 2020 study concluded that starvation was the most likely cause of the mass mortality event, based on the condition of the murre carcasses.

Before this marine heatwave, about a quarter of the world’s population, or about 8 million murres, lived in Alaska. The authors estimate that the population is now about half that number. Murre populations have fluctuated in the past, but the authors note that Alaska’s population has not rebounded as it did after previous small-scale extinctions.

The “warm blob” appears to have been the most intense ocean heatwave ever, but sustained warm conditions are becoming more common under climate change. A 2023 study led by California State University, including many of the same authors, showed that a 1 degree Celsius increase in sea surface temperature over six months causes mass mortality of several seabirds.

“Whether the warming is due to heat waves, El Niño, Arctic sea ice loss, or other impacts, the message is clear: Rising ocean temperatures will lead to large-scale changes in ecosystems and widespread impacts on seabirds. “It means a significant impact,” Parrish said.

“The frequency and severity of seabird deaths are increasing in tandem with ocean warming,” Parrish said.

A 2023 paper suggested that it would take at least three years for seabird populations to recover after a marine heatwave. Parrish said the fact that Alaska’s murres have not recovered from the “clump” seven years later is concerning.

“We are now at a tipping point in ecosystem reorganization, and it may be impossible to restore pre-extinction abundance.”

Other co-authors are Bree Drummond and Jared Laufenberg of the Alaska Department of Fish and Wildlife office. John Piatt, former federal scientist, currently with the World Puffin Council in Port Townsend. and Martin Renner of Tern Again Consulting in Homer.