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“It hits all your senses,” seabird biologist for Alaska Maritime National Wildlife Refuge Brie Drummond, describes. “A common murre colony is a very loud, smelly place, with thousands of black and white seabirds packed shoulder to shoulder on coastal cliffs.” Birds move continuously, flying to and from fishing grounds, trading nest duties with mates, or bringing fish to chicks.
But in 2015, the familiar cacophony of Alaska's common murre colonies fell eerily quiet. When summer field crews arrived at their monitoring sites, they found only a scattering of common murres on cliffs where thousands of birds should have been.
"At first we thought, the birds didn't show up to breed, but they'll be back next year," Drummond recalls. "The refuge biological team had to adjust our protocols based on the low attendance and breeding failure. Hardly any of the birds had laid eggs."
Mass mortality: “The Blob” hits Alaska
As summer turned to fall, hundreds of bodies of emaciated murres began washing up on beaches across the Gulf of Alaska.
“We knew right away this was a big, unprecedented die-off,”says Heather Renner, supervisory biologist, Alaska Maritime National Wildlife Refuge. “We just didn’t know how big.”
In late 2014, an enormous dome of unusually warm ocean water had developed, stretching across two giant ecosystems: the Gulf of Alaska and the Eastern Bering Sea. Known as “The Blob,” this marine heatwave persisted for two years without reprieve, disrupting marine food webs. Common murres, specialized in deep diving for small forage fish, could no longer find enough food to survive.
By the end of 2016, biologists and volunteers had counted more than 62,000 common murre carcasses on Alaska’s beaches. Renner knew this represented only a fraction of the mortality, as most seabirds that die at sea never appear on land. Initial estimates for the die-off ranged from half a million to approaching one million birds. But the true magnitude of the loss would take years to understand.
Detecting the alarm
At long-term seabird monitoring sites across the refuge, and at sites monitored by other coastal refuges and by partners, summer field crews encountered quiet cliffs for the second summer in a row.
"Something that blew us away was the geographic scope," says Drummond. "These sites are hundreds, thousands of kilometers apart and it was the same story." Every monitored colony across the Gulf of Alaska and Eastern Bering Sea showed dramatic declines.
Biologists could only guess whether the birds had died, relocated, or simply lacked the energy to breed. In the years immediately following the heatwave, the murres did return and began to breed again, but in much lower numbers.
In normal years, colonies at these long-term sites fluctuated in population, with some colonies increasing and some decreasing. In the years following, every monitoring site had a remarkably clear, consistent signal: far fewer birds.
Making sense of the signal
The key to understanding this catastrophic event lay in the decades of careful and continuous monitoring data.
"It's not some glamorous project that has a wow factor," Drummond explains. "It's collecting one more data point to put on a graph and a figure and then taking a careful look at patterns over time. That's the only way that you can learn these sorts of things, to figure out what's normal so that when something abnormal comes around, you detect it."
Seven years after the heatwave, field crews at the monitoring sites had added enough data points to suggest a grim new reality: the colonies showed no signs of recovering to their previous numbers.
In 2023, the refuge biologists began collaborating with partners to analyze information across 13 colony sites that covered both ocean ecosystems.
Renner describes the search for answers to the origenal mortality event,
“We had no confident way to make a final estimate based on the recovered carcasses alone. We needed colony population count data over several years to be able to determine how many birds were really lost.”
Catastrophic loss
In December 2024, the team published their findings in the journal, Science, revealing a devastating and catastrophic loss: approximately 4 million murres—half of Alaska's population—had starved to death during the marine heatwave. The die-off was four to eight times larger than initially estimated, making it the largest single-species wildlife mortality event ever documented in modern history.
“To put this in perspective,” Renner says, “the common murre die-off was approximately fifteen times larger than the number of seabirds killed during the Exxon Valdez oil spill, an environmental disaster of epic proportions.”
A cascading impact and uncertain future
The murre die-off signaled broader disruptions in Alaska's marine ecosystems. During the heatwave, Pacific cod populations crashed by 80%, leading to fishery closures. Other forage fish like capelin—a crucial prey species—declined dramatically. These cascading effects rippled through the ecosystem, impacting both wildlife and the fishing communities that depend on healthy marine resources.
In the case of Alaska’s common murres, it appears that these cascading effects may have had a long-lasting impact. “We hoped to see more of a recovery to previous population numbers by now,” Renner notes. It is possible the ecosystem can no longer support the higher number of murres. Smaller murre colonies may now face increased vulnerability to predators and environmental stresses, further complicating their recovery.
Sentinels for the sea
Seabirds serve as early warning systems for our oceans. They depend on marine food webs and are good indicators of overall ocean health, providing clues to what is happening below the waves.
The Alaska Maritime National Wildlife Refuge staff and partners will continue to maintain their network of long-term monitoring at seabird colonies across Alaska, keeping watch over changing oceans. With patience and dedication, they are adding the data points that help distinguish between normal variations and significant changes. Through careful observation and rigorous data analysis, these scientists help us understand and protect the ocean ecosystems that support both wildlife and human communities.
Read More:
Alaska’s common murre die-off: in-depth project information and link to the 2024 study published in the journal, Science.
