Seabird Die-Offs Linked to Marine Heat Waves

A new study, led by researchers at the University of Washington, has linked mass seabird die-offs to marine heat waves.

The study, published in the journal Marine Ecology Progress Series, analyzed data collected from residents along coasts from Alaska to central California from 1993 to 2021. The researchers were looking to find if these marine heat wave events were affecting seabirds, which are near the top of the food chain for coastal regions.

The analysis of over 90,000 surveys of beached seabirds shows the marine heat waves do impact the seabirds over time. The study found die-offs occurred more frequently following heat waves. In one particular case, the researchers found a sequence of die-offs 1 to 6 months and 10 to 16 months in the California Current, a marine ecosystem, after three prolonged marine heat waves.

“We find a dramatic delayed effect,” Julia Parrish, co-author and a professor of aquatic and fishery sciences at the University of Washington and executive director of the Coastal Observation and Seabird Survey Team (COASST), said in a news release. “A warmer ocean, and certainly a suddenly warmer ocean as happens during an El Niño or a marine heat wave, will result in the death of hundreds of thousands to millions of marine birds within one to 6 months of the temperature increase.”

The study authors have previously found links from warming ocean waters to die-offs in specific seabird species, such as common murres and Cassin’s auklets. The higher water temperatures cause changes to the availability of the birds’ prey, the previous studies found.

The most recent research takes a more general look at 106 different species around over 1,000 beaches. Seabirds started washing ashore usually a few months after a marine heat wave began, according to the data. Murres, puffins, auklets and shearwaters were among the most impacted species.

The die-offs happened for many reasons, such as algal blooms, diseases and starvation, all of which were linked to marine heat waves. Some of the worst massive die-offs, with more than 250,000 bird deaths, occurred about once per decade, except from 2014 to 2019, which had five massive mortality events.

“This is unprecedented,” lead author Timothy Jones, a University of Washington research scientist in aquatic and fishery sciences, said in a statement. “This type of massive die-off can be compared to a catastrophic storm that we would usually expect once per decade; they happen, causing massive damage, but usually there is enough time for areas to recover.” 

But in recent years, there’s less recovery time before another marine heat wave leads to massive damage. The study warns that with increasingly warming oceans, there could be more severe mortality events. Already this year, ocean surface temperatures reached a record high, and El Niño could bring more record-breaking temperatures.