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12 Jan, 2016 19:12

Mass die-off of seabirds attributed to starvation, possibly related to climate change

Mass die-off of seabirds attributed to starvation, possibly related to climate change

Warming water temperatures are believed to have decimated the stock of fish eaten by common murres in Alaska. Lack of food has led to about 8,000 dead murres being found in just one location – part of the most extreme die-off in 40 years, one expert says.

In Alaska, there are about 2.8 million breeding common murres, a land-averse seabird that dives as deep as 600 feet underwater to find prey, such as herring and capelin. Thousands of murres were recently discovered dead on a beach in Whittier, Alaska, according to the Associated Press. Others were emaciated, suggesting a change in diet that the murres could not handle.

"That's unprecedented, that sheer number in one location is off the charts," said John Piatt, research wildlife biologist at the US Geological Survey's Alaska Science Center, referring to the 8,000 dead murres in Whittier. Piatt told the Alaska Dispatch News the die-off is "the most extreme I have ever seen or heard of" in four decades of research in the Atlantic and Pacific Oceans.

Federal researchers are trying to assess the extent of the die-off while stopping short of offering an estimate of how many have perished, the AP reported. Researchers are planning to comb more Alaska beaches for signs of murres in peril. Last summer, murre carcasses were found throughout Alaska, including on Kodiak Island, the Alaska Peninsula, and elsewhere. Large accumulations of dead murres have appeared in Homer’s Mud Bay and Kachemak Bay, and elsewhere along coastal Alaska as of late.

“It’s turning out to be something that does have the potential for population-level effects,” Andrea Medeiros, a spokeswoman for the Fish and Wildlife Service, told Alaska Dispatch News. “It is just off the chart as far as what we typically see with these events.”

While winter storms can impact murres’ hunting strategies, this die-off is showing signs of starvation likely caused by an extraordinary warming of surface water temperatures – possibly due to climate change or an El Nino weather pattern in the central Pacific Ocean – that has diminished the populations of capelin and other forage fish sought after by murres.

"If the water (temperature) goes above that threshold, they're out of there," said biologist David Irons, who noticed the mass die-off in Whittier. "They either die or they move."

Many stranded murres have been collected by wildlife treatment outlets over the past year. A US Geological Survey examination of around 100 carcasses found no sign of parasites or disease that would suggest a cause for the latest die-off.

Irons led a research effort in 2008 that showed a correlation between natural murre die-offs and rising ocean temperatures connected with climate change. When ocean surface-water temperatures rose a few degrees, murres showed depleted numbers, Irons found. Given no one monitors numbers of forage fish in Alaska, the large number of dead murres points to a lack of prey. Murres need to track large schools of fish, as they eat as much as 30 percent of their body mass per day.

"So when they're gone, no one has any information on them to show that they're gone, except birds are showing us they're gone," Irons said.

Water temperatures in 2015 were above average overall, and, prior to the die-off, murres were found in uncommon areas. In addition, many females were too weak to breed last year, according to Kathy Kuletz, a biologist for the US Fish and Wildlife Service.

"The length of time we've been seeing dead birds, and the geographic scope, is much greater than before in other die-off events," said Kuletz. "We're looking at many times that. So possibly a good chunk of the population."

The approximately 2.8 million common murres in Alaska are part of a population of as many as 20 million of the birds worldwide, AP reported.