Millions of Alaska's seabirds starved to death after intense heat wave

Common murres, resembling flying penguins, thrive in coastal ecosystems, where they dive into the ocean for fish and nest in large colonies along cliffs. Despite their robust appearance, these seabirds face immense threats from warming ocean conditions.

A new study, led by the U.S. Fish and Wildlife Service, sheds light on the devastating effects of marine heat waves on common murres in Alaska.

Counting murre carcasses

The University of Washington’s Coastal Observation and Seabird Survey Team (COASST), a citizen science initiative, played a vital role in uncovering the crisis.

Coastal residents trained by COASST documented alarming numbers of murre carcasses on beaches. In 2020, COASST and other observers reported a mass mortality event, identifying over 62,000 murre carcasses along the West Coast and Alaska.

In some areas, carcass counts exceeded normal levels by more than 1,000 times.

Impact of heat waves on common murres

The 2020 study, while highlighting the severity of the event, did not determine the total loss following the 2014-2016 marine heat wave known as “the blob.”

The new study fills that gap. By analyzing data from 13 murre colonies surveyed between 2008 and 2022, researchers estimate that 4 million common murres – half of Alaska’s population – died.

In the Gulf of Alaska, colony sizes declined by 50%, while colonies in the eastern Bering Sea saw a staggering 75% decline. The rate of recovery currently remains unknown.

“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 co-author of the 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.”

“Warm blob” and its aftermath

The “warm blob,” a patch of unusually warm water spanning from California to Alaska, disrupted ecosystems during its peak from late 2014 through 2016.

It caused decreased ocean productivity, which led to food shortages for marine predators, including seabirds. Analysis of murre carcasses confirmed starvation as the primary cause of death during the mass die-off.

Before the heat wave, Alaska housed about 8 million common murres, roughly a quarter of the global population. The murre population in Alaska has since halved in size.

Unlike previous, smaller die-offs, where murres rebounded, they do not appear to be recovering after this event.

Climate change intensifies marine heat

The “warm blob” represents one of the most extreme marine heat waves recorded, but similar events are becoming more frequent due to climate change.

A 2023 study, led by many of the same authors, revealed that even a 1°C increase in sea surface temperature over six months triggers seabird mass mortality events.

“Whether the warming comes from a heat wave, El Niño, Arctic sea ice loss or other forces, the message is clear: warmer water means massive ecosystem change and widespread impacts on seabirds,” Parrish stated.

“The frequency and intensity of marine bird mortality events is ticking up in lockstep with ocean warming.”

Troubling lack of recovery

The persistence of Alaska’s murre population decline highlights a critical challenge.

The 2023 study suggested seabird populations typically need at least three years to recover from a marine heat wave. However, seven years after “the blob,” Alaska’s murres show no signs of bouncing back.

“We may now be at a tipping point of ecosystem rearrangement where recovery back to pre-die-off abundance is not possible,” Parrish warned.

Saving common murres from heat waves

This study highlights the devastating and lasting impacts of marine heat waves on common murres and other marine species.

With ocean warming intensifying under climate change, the frequency of such events will likely increase. Understanding these changes can inform conservation efforts and mitigate future impacts on vulnerable species.

Furthermore, coordinated global efforts are essential to address climate change and safeguard marine ecosystems for future generations.

Co-authors of the study include Brie Drummond and Jared Laufenberg from the U.S. Fish and Wildlife Service, John Piatt from the World Puffin Congress, and Martin Renner of Tern Again Consulting.

The study is published in the journal Science.

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