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A number of grey whales have died and washed ashore in B.C. this year.

Dozens more have similarly ended up beached on the coasts of Alaska, Washington, Oregon, and California during the same period.

And on the west coast of Mexico, yet more.

Nobody knows how the 147 large marine mammals have died during just the last five months (December 17, 2018, to May 27, 2019).

Now the U.S. National Oceanic and Atmospheric Administration (NOAA) has declared the deaths an “unusual mortality event” (UME) and announced its scientists will investigate the matter.

“The Marine Mammal Protection Act (MMPA) defines a UME as a stranding event that is unexpected, involves a significant die-off, and demands immediate response,” reads May 30 NOAA media release.

“Given the increased strandings, NOAA Fisheries convened a UME Working Group of marine mammal experts to assess seven criteria to determine whether a UME should be declared, as outlined in the MMPA.

“The working group members include experts from scientific and academic institutions, conservation organizations, and state and federal agencies who work closely with stranding networks and have a wide variety of experience in biology, toxicology, pathology, ecology, and epidemiology,” it continues.

NOAA staff will coordinate their investigation with counterparts in Canada as well as Mexico, according to the release.

“Each spring eastern North Pacific gray whales migrate 10,000 miles or more along the West Coast from winter waters in Mexico where they give birth to summer feeding grounds in the Arctic off Alaska,” NOAA explains.

“The whales rely largely on their summer feeding in the Arctic to last them throughout the year because they do not feed extensively while migrating or wintering in Mexico. Many gray whales that have stranded this year during their northbound migration have been skinny and malnourished, with some showing signs of emaciation.

“That suggests that some whales may be exhausting their energy reserves this year before they reach the Arctic to resume feeding, researchers say,” the release adds.

National Oceanic and Atmospheric Administration

Reaching weights of 36 tonnes, the grey whale is one of the largest animals on Earth (but only half the size of the blue whale).

It was once at risk of extinction but has recovered in recent decades. The grey whale was removed from the United States' government's endangered species list in 1994. NOAA estimates some 27,000 live off North America's west coast.

The research organization’s investigation will focus on learning possible causes of the strandings. It will also make additional resources available for NOAA staff to respond to grey whale deaths as they continue to occur.