Marine heat waves are causing a ‘wreck’

Researchers blame rise in ocean temperatures for massive bird die-offs

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Marine heat waves are causing a ‘wreck’

With the ability to dive upward of two football fields below the ocean’s surface to forage, common murres are a force to be reckoned with.

That is why, when 1 million of the penguin-like birds died in 2015 and 2016, scientists began looking for answers. 

New research by scientists from several institutions including the UW blames an unexpected food pattern interruption caused by a long-lasting marine heat wave called “the blob.”

The findings were published Jan. 15 in the journal PLOS ONE.

“My role was to lead one of the citizen science organizations that contributed long-term baseline data, as well as data collected during the die-off,” professor in the School of Aquatic and Fishery Sciences, associate dean of the College of the Environment, and co-author of the article Julia Parrish said. “That organization is the Coastal Observation and Seabird Survey Team.”

The study analyzed murre die-off in terms of spatial extent, duration, absolute numbers, and magnitude of deposition on beaches relative to expected amounts. 

Researchers found that the combination of fewer foraging fish for the murres to feast on and increased competition from other fish predators like Pacific cod led to mass mortality events due to starvation. 

“A persistently warmer ocean led to a shift in which lower trophic species dominated, culminating in different types of forage fish,” Parrish said. “This meant the murres ran out of food.”

And to make it worse for the murres, warmer waters speed up the metabolisms of other predatory fish like Pacific cod and pollock, leading to an unbalanced supply-demand ratio. 

“When big predatory fish get warmer, their metabolism increases and they need to eat more,” she said. “So these fish became more serious competitors with the murres for access to the forage fish.”

The heat wave also reduced the nutrition available from zooplankton since it stunted their growth. 

Many of the birds that died were of breeding age, and the study’s authors found that the shift in food availability reduced the murres’ ability to reproduce during and after the heat wave. 

“It suggests that young-of-the-year were scarce, which we know was true because so many colonies failed to produce chicks,” Parrish said. “The second thing it suggests is that the environment really was quite different, and less hospitable, for murres in general. This is because adults usually have a pretty high annual survival rate, but not in 2015-16.”

According to the National Park Service, seabirds are excellent indicators of ocean ecosystem health, but over five years of mass mortality events are pointing to “significant changes in marine ecosystems.”

Scientists are continuing to research ocean ecosystems, but Parrish emphasized that without public involvement in science, research of this sort would not be possible. In the case of the murre die-off event, citizens from Alaska to California searched beaches for bird carcasses and helped scientists collecting data. 

The official term for a massive bird die-off is a “wreck,” and Parrish said that the term is “gruesomely accurate.”

Like a shipwreck covers a beach with debris, a wreck of birds literally means that the beach is covered with bodies,” she said. 

Reach contributing writer Karina Patel at science@dailyuw.com Twitter: @karinappatel

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