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Dr. Kathy Burek, a veterinary pathologist, slices through the blubber layer on a gray whale that was beached outside Anchorage, Alaska, earlier this month. Scientists are trying to figure out why so many gray whales are dying.

Nat Herz/Alaska’s Energy Desk

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Nat Herz/Alaska’s Energy Desk

Dr. Kathy Burek, a veterinary pathologist, slices through the blubber layer on a gray whale that was beached outside Anchorage, Alaska, earlier this month. Scientists are trying to figure out why so many gray whales are dying.

Nat Herz/Alaska’s Energy Desk

Cutting through a 6-inch-thick layer of blubber demands a sharp knife.

But as veterinary pathologist Kathy Burek prepared to slice into the abdomen of a dead gray whale, many of her knives were dull. Burek had used them two days earlier to collect samples from a different gray whale, 100 miles away. Then, another whale beached outside Anchorage, Alaska.

“I didn’t have time. That’s what our problem is right here,” Burek said as she struggled to pull off a slab of blubber.

As of the end of May, four dead whales had been found thus far in Alaska. But those come after at least 60 other whale deaths along the West Coast this year, according to the National Oceanic and Atmospheric Administration. That is the highest number in two decades.

Scientists say more deaths are likely in Alaska, since each spring, gray whales swim 5,000 miles from Mexico to their Arctic feeding grounds.

“The level of strandings we’ve seen on the West Coast means Alaska should brace itself for probably some significantly elevated numbers of gray whale strandings,” said John Calambokidis, a research biologist at the Washington state-based Cascadia Research Collective.

A dead whale at the mouth of the Placer River, at the eastern end of the Turnagain Arm, near Anchorage, Alaska. The deaths of at least 60 whales along the Pacific Coast this year have scientists concerned and looking for answers.

Nat Herz /Alaska’s Energy Desk

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Nat Herz /Alaska’s Energy Desk

A dead whale at the mouth of the Placer River, at the eastern end of the Turnagain Arm, near Anchorage, Alaska. The deaths of at least 60 whales along the Pacific Coast this year have scientists concerned and looking for answers.

Nat Herz /Alaska’s Energy Desk

Burek was hired by NOAA to take samples from the stranded whale outside Anchorage. The whale had been floating for nearly two weeks, and Burek wasn’t planning an extensive necropsy — the animal version of an autopsy.

“It’s just not worth the time and effort because once we get inside the abdomen — the kidneys, the liver are just going to be kind of liquefied,” she said.

The whale, she added, looked “skinny.”

Experts say it appears that many of the other gray whales died of starvation. But scientists aren’t sure why.

Reaching “carrying capacity” or climate change?

Gray whales were once hunted nearly to extinction by whalers. But they were protected by the Endangered Species Act, and the eastern North Pacific population rebounded and was removed from the endangered species list in 1994.

These days, the overall eastern North Pacific stock of gray whales is healthy and estimated at 27,000, according to NOAA. They rebounded from a similar spike in deaths in 1999 and 2000, and scientists think it’s possible they’ve simply reached what’s called “carrying capacity” — the maximum number the whales’ habitat can sustain.

But researchers are also asking whether recent warming trends in the Arctic and reduced sea ice may have affected the whales’ prey.

“We have to really be on top of: Is there any relationship to climate change? And does this link to any other factors that might be affecting other species as well?” Calambokidis said. “Could gray whales be an early warning sign of other things that we need to be watchful for?”

Each spring and fall, the whales swim on one of the longest known mammal migrations — between their winter area in Baja California, Mexico, and their summer feeding grounds in the Chukchi, Beaufort and Bering seas in the Arctic. They primarily eat tiny, shrimplike creatures called amphipods, sucking them off the ocean floor and filtering mud and seawater out through their baleen.

The Arctic is warming at twice the rate of the rest of the world, and temperatures in the Bering Sea last summer were especially high — as much as 9 degrees above normal. In the previous winter, ice levels were the lowest ever recorded.

NOAA surveys the gray whales’ feeding patterns each summer. Last year’s survey results are now getting scrutinized to see whether they can help explain this year’s deaths, said Michael Milstein, a NOAA spokesman.

“The scientists that do those surveys are going back through their records and trying to understand if there was something unusual about when and where the whales were feeding,” he said.

A sample of abdomen muscle from a beached whale in Alaska. The sample will be tested for potential clues to the whale’s death.

Nat Herz/Alaska’s Energy Desk

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A sample of abdomen muscle from a beached whale in Alaska. The sample will be tested for potential clues to the whale’s death.

Nat Herz/Alaska’s Energy Desk

Milstein said they’ll be doing another survey this year, trying to determine whether more whales are competing for limited resources. Or if, for some reason, the food is less nutritious or not providing whales the energy needed to sustain them on a long migration.

NOAA also hopes to gather information from dead whales, like the one beached outside Anchorage. Initially, Burek wasn’t optimistic about the quality of samples she would get, but it turned out that the whale was in better shape than she thought.

After cutting and peeling a swath of blubber off one side, Burek cut into the whale’s abdomen, which released periodic spurts of gas and a foul smell. Internal organs slowly slid out of Burek’s incision.

“Ooh, guess what that is — that’s the kidney!” Burek said, as she sliced into the big red mass. “We got kidney!”

Burek placed tiny chunks into bags and vials — muscle, testicle, even poop. They’ll be tested later, as potential clues for researchers trying to solve the mystery of why whales are dying.

Reporter Tom Banse contributed to this story.