Researchers work to pinpoint cause of seabird die-off in Bering Sea

Published: Aug. 13, 2018 at 3:46 PM AKDT
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Since May, more than 1,400 seabirds have been found dead around the northern Bering and Chukchi Seas. The deaths have been seen across large areas and a variety of species, including common and thick-billed murres, black-legged kittiwakes and short-tailed shearwaters.

“These are not exceptionally large numbers but it is widespread throughout the area and extending down into the Pribilof Islands, and now we're getting reports in the Gulf of Alaska, different species,” says Kathy Kuletz, wildlife biologist with the U.S. Fish and Wildlife Service. “It's a concern because it's widespread and it's occurred over a long period of time. We've had bird die-offs in the past going back to the 70s that were much larger, but not so far north and usually not so many species and so many areas.”

Some of the bird carcasses were sent to a lab to determine the cause of death. All of the birds were severely emaciated, but the cause is still yet to conclusively be determined. Was it lack of food or a disease causing them to starve?

Officials are waiting on the rest of the results but they’ve gotten a few birds back from the lab.

“The birds do not have an illness. They do not have avian cholera,” says Gay Sheffield with Sea Alaska Grant, University of Alaska Fairbanks. “They do not have influenza. It's just starvation.”

But Sheffield cautions they are still waiting for results on the bulk of the birds sent in.

The lab is also doing further testing to check for toxins, such as an algae bloom, but according to Kuletz, those situations tend to be confined to one area.

“Usually that's more of a local occurrence though and this has been so wide spread across the board for different types of foraging and different types of foragers,” says Kuletz. “So it seems lack of food or a different distribution of the food is what's causing the die-offs.”

According to Kuletz, large volume sea bird die-offs in the past have been associated with warm ocean temperatures. “That can result in fewer plankton or smaller plankton that are less fatty and that's a problem for all the way up the food chain, for fish and for birds, marine mammals,” she says.

This past winter, the northern Bering and Chukchi Seas had record low sea ice, the lowest in 150 years according to Rick Thoman, Climate Science and Services Manager with the National Weather Service. “The ice cover or lack there of also affects the water temperature farther down in the ocean, not just at the surface,” Thoman said. “Without that ice cover, that deeper water, especially in the northern and central Bering Sea, is going to be much warmer than it would be otherwise.”

What typically forms is the “cold pool,” a salty, heavy brine that flows down the Bering Sea. This year, that didn’t happen.

NOAA Fisheries conducts an annual fish survey in the eastern Bering Sea.

“We’ve done this survey for 37 years now and this is the first year on record where we have not had a cold pool,” says Dr. Lyle Britt, fisheries research scientist.

Not having that cold water meant some fish species moved into new areas, and in some areas where they expected to find certain kinds of fish, the fish weren’t there.

“We’re seeing species we would normally associate with the south — large pollock, Pacific cod, yellow fin sole,” Britt said. “We have not been seeing much of the species you normally think of as cold pool species that are also prey for birds.”

Britt emphasizes that all the surveys in the northern Bering Sea aren't completed yet, and the data hasn’t been fully reviewed. The fish might have moved to a different part of the region.

Thoman says the sea ice forecast for the coming winter is far below average, but not as low as we saw last year.