In early 2016, Sarah Schoen, a wildlife biologist at the Alaska Science Center, a branch of the United States Geological Survey, in Anchorage, set off on an investigation of a large die-off of murres, a black and white penguin-like bird, reported near the coastal city of Whittier.

Even by Alaska standards, it was a lousy day for cruising in an open boat along the shore of the Gulf of Alaska. The temperature hovered around freezing. Rain alternated with snow. Schoen, who normally counts healthy birds breeding and caring for their young, steeled herself for the sight of corpses. Still, she was staggered by the spectacle she found.

“There were dead birds on every beach we looked at,” she recalls. On one rocky stretch 100 yards long, she found 750 birds in piles.

The bodies were emaciated, as though the birds had starved, a finding confirmed by subsequent necropsies.

And the grisly scene was hardly an isolated one.

Surveys conducted by Schoen and dozens of other field scientists and volunteers found that 62,000 murres perished in a vast die-off that stretched from the Bering Sea to southern California. Taking into account that only a tiny fraction of birds that died in the event drifted to where observers could count them, researchers estimate that 1.2 million murres succumbed – about 10 to 20% of the West Coast and Alaska populations.

Though mass bird die-offs occur every once in a while, the size and extent of this one was “off the charts,” says John Piatt, Schoen’s boss and lead author of a PLOS ONE paper about the event. He and his coauthors found only one other comparable bird die-off in history, along the coast of France, also in 2014.

Even more astounding was the precipitous plunge in murre breeding success in subsequent years. Common murres mate in large colonies, usually on rocky cliff faces. In nearly a century surveying such gatherings all over the world, biologists have recorded only a few instances in which a colony completely fails, not producing a single chick. Only one of these was in Alaska. Piatt says that between 2015 and 2017, 22 colonies – including one with one-million birds – failed at least once. “That is astonishing,” he says. “There is nothing that even comes close in the history books for this species.” He says that normally, a million-bird colony would produce 250,000 chicks.

Other species on the West Coast and Alaska also took a battering about that same time. In Glacier Bay and Icy Strait, Alaska, a steady 30-year growth in the humpback whale population ended abruptly in 2013. Biologists reported that the remaining whales were “skinny,” indicating malnourishment. By 2017, the humpback population there had declined by 40% and the reproductive rate had crashed. In California, 10 times more than the normal number of sea lions ran aground in 2015. They were emaciated, dehydrated, and underweight. In the Gulf of Alaska, fishermen netted record low, and declining catches of Pacific Cod. Hoping to let the fishery recover, the federal government halted trawling for cod there in December 2019.

Blame ‘the Blob’

What could have caused massive die-offs and multi-species declines across such a huge geographic area? Researchers suspect the culprit was an ocean phenomenon nicknamed “the Blob.”

In late 2013, the Pacific Ocean unexpectedly heated up in a huge oval area stretching west for hundreds of miles from near Juneau. The area grew warmer and larger, and it twisted its axis by 90 degrees. By early 2015 the hot region was as large as the continental United States hugging the West Coast from Anchorage to the U.S. border with Mexico. Large swaths of water climbed more than 3°C (5.4 °F) above normal, a remarkable increase for such a large patch of ocean. Lasting an unprecedented 700 days, the Blob was the longest episode of intense ocean heating – an event scientists call a marine heat wave – ever recorded.

Researchers say the Blob appears to have been caused by a combination of several independent factors. Beginning in 2013, an unusual high pressure system scientists have dubbed the “Ridiculously Resilient Ridge” blocked winds that normally whisk warmth poleward. The El Niño weather pattern that began 2015 was the second-strongest on record. El Niños warm parts of the eastern Pacific, including the U.S. Pacific coast. And global warming has steadily raised ocean temperatures. More than 90% of the extra heat trapped by greenhouse gasses that people pump into the air ends up in the ocean. Climate change has warmed the Pacific off the U.S. coast by 0.5-0.7 degrees Celsius. “If we didn’t have this baseline warming,” says Nicholas Bond, a research meteorologist at the University of Washington who gave the heatwave its nickname, “the Blob wouldn’t have been as severe.”

Biologists are still piecing together just how the high water temperatures damaged wildlife. But it seems that, at least in some cases, the higher temperatures rejiggered the availability of food.

Invasion of the sea pickles

Richard Brodeur, a biologist at NOAA’s Northwest Fisheries Science Center in Seattle, says the wildlife declines began at the base of the marine food chain with the shrimp-like krill that filter-feeding whales – including humpbacks – eat by the millions. Krill are also a major part of the diet of some birds and small forage fish that, in turn, feed seabirds and larger fish. For several years beginning in 2015, krill numbers plummeted in the eastern Pacific along the U.S. coast. Nobody knows what happened to these energy-rich phytoplankton. Brodeur says that they may simply have descended to deeper waters below researchers’ nets. “But this raises a problem for predators such as birds that cannot dive very deep,” Brodeur says. The gelatinous sea pickle, normally a resident of tropical waters south of California, and jellyfish, took their place. The sea pickle “had never been reported in our area before,” Brodeur says. “They’ve changed the ecosystem completely.”

The PLOS ONE paper conjectures that this change in food availability along with other impacts of the heat traveled up the marine ecosystem, with profound results from the bottom to the top of the food chain. “It was like putting a stick in the spokes,” lead author Piatt says.

The high temperatures raised the metabolism of anchovies, smelt, sardines, and other forage fish, Brodeur says, increasing their need for food. But with fewer krill and other phytoplankton to eat they were forced to dine on the less nutritious jellyfish (Brodeur says sea pickles are probably too big for them). Then the forage fish were not only underfed but overharvested by their predators, such as cod, pollock and flounder, whose metabolisms also spiked in the heat. For two years the all-important forage fish became scarcer and were unusually gaunt.

“That was the bottleneck,” says Rob Suryan, a co-author of the PLOS ONE paper. “It left far less energy that could be transferred to the birds and mammals.”

And that proved catastrophic for the murres, as the birds consume half their body weight in fish every day.

“If they don’t eat in three or four days, they’re dead,” Piatt says. With so few krill available and forage fish scarce, murres starved. Most likely, many of the survivors were too enfeebled to breed.

The story was similar with that of marine mammals. Broduer says that whales swam unusually close to shore and into estuaries, probably seeking a meal anywhere they could.

“That’s not normal behavior,” he says. Some of them died tangled in fishing gear. The National Oceanic and Atmospheric Administration reported that whale entanglements on the West Coast doubled over the previous year in 2014, and doubled again in 2015.

Worrisome future

The damaged West Coast and Alaska ecosystems have partially recovered since the 2014-2016 heat wave. But Piatt fears a repeat.

“That’s got my attention,” he says. “If we have another jolt like this,” he says, “it doesn’t look good.”

The Pacific off the West Coast and Alaska was unusually warm again in late 2019, provoking concern about a repeat of the Blob. Piatt says it’s not yet clear whether this heat wave will be as bad. “The jury is out on how this most recent heatwave is going to play out,” he says.

A 2018 paper in the journal Nature Communications reported that the number of marine heatwaves increased globally by 34% between 1926 and 2016. Another 2018 paper, in the journal Oceanography, stated that global warming will make marine heat waves “more intense over time.”

Bond, the University of Washington research meteorologist, says that temperatures in that event will become the norm in the next several decades. “When we have an event on top of that, it’s going to be a different ocean,” he says. “How much the species can adapt to that how much it will result in wholesale reorganization of marine communities, we’re trying to figure that out.”

Tom Toro is an independent cartoonist and writer whose work includes more than 200 cartoons published in The New Yorker since 2010.

Editor’s note: Financial support for reporting on this article was provided to the author by Abby Rockefeller and Lee Halprin.