100s of Dead Whales Are Washing up on the West Coast—Scientists Don't Know Why

A dead whale washed up on the shores of the San Francisco Bay Area last Friday, marking the 12th such incident in the region so far this year.

The death is just one of many in what scientists have called an Unusual Mortality Event (UME) along the west coast of North America. Since 2019, it has seen hundreds of gray whale deaths.

Reports on Friday, May 21, said the gray whale had washed up on Pacifica State Beach. It was a 47-foot male according to tissue samples, Giancarlo Rulli, a spokesman for The Marine Mammal Center, told CBS Sacramento.

Marine biologists often conduct an examination called a necrospy to try and find out more about what caused the whale to die. However, a necrospy was not possible in this case because the animal had been dead for too long.

The whale becomes the tenth gray whale to be reported dead in the San Francisco Bay Area in 2021, in addition to one pygmy sperm whale and a fin whale, according to Bay Area news outlet The Mercury News.

The U.S. National Oceanic and Atmospheric Administration (NOAA) has said elevated numbers of gray whale strandings—in which whales get stranded on land—have taken place in the current UME since January 1, 2019, from Mexico through Alaska.

As of May 6, 2021, the NOAA reported a total of 454 gray whale strandings across Canada, the U.S., and Mexico. That figure will almost certainly have increased.

While it has not been possible to identify the cause of death for all of these animals, a number of them are suspected or determined to have been killed by ships.

The NOAA also said early findings have shown "evidence of emaciation" in several whales studied, meaning they appeared abnormally thin or weak. The agency said more research was needed because such findings are not consistent across all whales examined.

In April, researchers concluded that a fin whale that washed up near Fort Funston, California, on April 23 had probably died after it was struck by a ship. They found that the whale had suffered trauma to its neck.

That incident was the fifth whale death in the Bay Area in April alone.

Likewise, the gray whale which landed on the Pacifica State Beach on Friday is the fifth to be reported this month, The Mercury News reports.

A UME is defined by the Marine Mammal Protection Act as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response."

Anyone who spots a stranded or floating whale should report it immediately, the NOAA states. Contact details can be found here.

Update 1/6/2021, 11:22 a.m. EDT: This article has been updated to clarify information about the date of the whale's discovery.

Gray whale
A stock image shows a gray whale, seen from above, spraying water. An increase in the animals' deaths across the west coast of North America since January 2019 has led to an unusual mortality event (UME) being declared. rainngirl/Getty