Scientists still aren’t sure what’s killing hundreds of gray whales along the West Coast

A gray whale breaches the surface.
A gray whale breaches the surface. (Public domain photo by Merrill Gosho/Alaska Fisheries Science Center, NOAA Fisheries Service)

A gray whale stranded in Twentymile River near Girdwood over Memorial Day weekend was reported dead in Cook Inlet earlier this month. The young male whale was first spotted by boaters a mile upstream from the Seward Highway bridge on May 25.

National Oceanic and Atmospheric Administration fisheries scientist Barbara Mahoney said it likely swam upstream during a very high tide and was trapped there when the water receded. She and a team of scientists monitored the whale for a week while it slowly made its way back downriver during high tides.

“It looked like it was patiently waiting for the tide, in the sense that it was submerged, it had two and a half, three feet of water,” she said.

At low tide, Mahoney says she saw half the gray whale’s body, including its blowhole, above the water surface. The whale was able to breathe the entire time, she says, and the coursing river kept its body from drying out.

A week later the tide finally pushed the whale into Turnagain Arm. Mahoney was hopeful the animal would make it into Lower Cook Inlet, but on June 12 got a call from a pilot reporting a dead whale near the mouth of the Susitna River.

Hundreds of gray whales have washed up dead along the West Coast since last year, causing the National Oceanic and Atmospheric Administration to declare an “unusual mortality event.” Like many of the other beached gray whales, Mahoney said this one looked skinny.

That’s one possible reason the whale strayed so far into Upper Cook Inlet — it was looking for food. Mahoney says other hungry gray whales have been spotted in unusual places since the beginning of the mortality event.

“One or two whales stayed in King Cove for quite a few weeks, if not over a month, you know, feeding. And they’ve never had a record of these whales in their cove, nevermind staying for so long,” Mahoney said.

The 2019 mortality event included more than 200 gray whale strandings, the most since 2000, according to NOAA. There have been 12 whales stranded in Alaska so far in 2020. This time last year, there had been 16.

Scientists are still unsure what’s causing the die-off. One theory is that the population of gray whales got too big for the ecosystem to support it. Researchers are also looking at the relationship of receding sea ice to food availability for whales that feed in the Arctic during the summer.

John Calambokidis is a research biologist at Cascadia Research Collective in Washington state. He said one of the reasons for the mystery is that dead gray whales are hard to study.

“It has been very challenging both last year and this year to find and fully examine animals in fresh conditions to completely rule out, you know, all causes of disease or other factors like that,” Calambokidis said.

Researchers managed to capture some of the Twentymile gray whale’s exhaled breath using a drone while it was stuck in the river. Mahoney is hoping to learn about the whale’s body condition and cause of death from that sample, but she says it will be difficult to get any other usable samples from its body before it decomposes.

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