Massive Murre Die Off Last Winter Caused By Warm Water Disrupting Food Chain And Causing Starvation
The seabirds that died by the hundreds of thousands last winter in the Gulf of Alaska appear to be the latest victims of what they're calling "the blob," a huge body of warm ocean water that dominated North Pacific marine systems during the last few years.
That's the implication of a paper presented by Shannon Atkinson of the University of Alaska Fairbanks at the Alaska Marine Science Symposium this week.
Atkinson and her colleagues looked at the bodies of dead common murres that showed up in huge die-offs first noticed in Seward, but soon found on many beaches, some of them quite remote.
"The birds were underweight to the point of starvation," Atkinson said.
The number of starved murres, and the length of their die-off, was something no one had seen before, but murres in the Gulf of Alaska were not the only seabirds to die in large numbers last year. Tufted puffins in the Bering Sea also showed up on beaches in large numbers.
But the murres were particularly troubling. Scientists struggled to understand why a bird that spends most of the winter offshore eating fish would fly to the coast to die of starvation on the beach.
Atkinson says that when their research showed a link between the starving birds and trawl surveys that came up empty, or with only a few of the forage fish normally eaten by murres, they had their smoking gun.
"The main result to take away from this is the catch per unit effort for all of these species was very close to zero, meaning that the forage fish was simply not there," Atkinson said. "And so all of these little red dots are basically zeros. Or you may as well make them little X's in the eyes of common murres."
The poor number of forage fish was due to several years of unusually warm water associated with the blob, which dominated the Gulf. That body of warm water was created by a combination of factors that Atkinson calls "The Perfect Storm."
Until the blob appeared and worked its way north up the coast, sea temperatures had been rising gradually as a result of climate change. The blob heated everything up and stayed long enough to change the types of plankton in Alaskan waters. Instead of the big fatty cold water copepods that are normally found here, the sea had lots of smaller, less fatty, warm water varieties. That meant less food for the fish that murres eat.
The blob may go away, but it's already spread the shift to smaller, less fatty copepods and krill all the way to Saint Paul Island in the Bering Sea.
"[There were] dead birds all around. And there were so many that even the fox were having trouble keeping up with eating them all," Atkinson said. "So it was clearly throwing that ecosystem into an imbalance."
The good news is that so far there is no data indicating that warmer waters have hurt salmon runs, though there is concern that salmon may be getting smaller as a result.