Murre die-off led to survivors' reproductive failure
The massive die-offs that left Alaska beaches coated with tens of thousands of murre carcasses in 2015 and 2016 also took a big toll on the birds' next generation when survivors failed to breed. There was a near-total reproduction failure last year at all of the monitored breeding sites in the Gulf of Alaska and Bering Sea, federal biologists report.
At about 20 of the rocky outcroppings where common murres nest, lay eggs and hatch chicks, almost no fledglings were found, said Heather Renner, a wildlife biologist with the U.S. Fish and Wildlife Service.
Murres are black-and-white seabirds related to puffins and auks, are better at diving than flying, and look a bit like penguins. They are plentiful in Alaska's waters, normally numbering about 2.8 million, according to the Fish and Wildlife Service.
"All of the colonies that I'm aware of in the Gulf of Alaska had complete failures, and also the Bering Sea," said Renner, who is based in Homer and works at the Alaska Maritime National Wildlife Refuge.
Biologists had never documented such a widespread reproductive wipeout for common murres in Alaska, she said. Exactly why such a failure occurred is not yet known but is believed to be linked to lack of food connected to the "long, extended period of warm water," she said.
Normally, about half of common murre nests successfully fledge chicks, she said. And murres in the Aleutian Islands and Chukchi Sea reproduced normally last year, despite the problems in the Gulf of Alaska and Bering Sea, she said.
The grim news about the Gulf and Bering Sea murres' reproductive failures was reported last week at the Western Alaska Interdisciplinary Science Conference and Forum held in Unalaska.
The common murre die-off of 2015 and 2016, linked to unusually warm conditions in the marine environment, was the biggest on record in Alaska. Nearly 42,000 carcasses were collected, and far more dead birds went uncollected, Renner said. Starving but still-alive murres were found in inland spots, far away from their marine habitat, an indication of fruitless searches for food.
The die-off coincided with the presence of a large mass of warm water in the North Pacific that lingered from late 2013 to 2016. Nicknamed "the Blob," it combined with another phenomenon that also warmed the region's waters, one of the most powerful El Nino systems on record.
Several other animal die-offs during that period were also linked to the warm conditions. Dozens of large whale carcasses were found floating or beached in the Gulf of Alaska, and toxins from warm-water-stimulated algal blooms are leading suspects in those deaths, now classified as an "unusual mortality event" being investigated by scientists. Hundreds of emaciated puffins turned up dead on St. Paul Island in the Bering Sea last year, and warmth-related lack of food is considered the likely cause.
Mass strandings of starving sea lions and seals occurred on the U.S. West Coast, a phenomenon also blamed on warm water.
As for Alaska's common murres, they are now making their spring return from southern wintering grounds, Renner said. Murres flew into Kachemak Bay about two weeks ago and they appear to be healthy, she said.
"I've seen them arriving at the right time and looking normal, so fingers crossed," she said.