In the span of eight days, four gray whales were found dead in the San Francisco Bay area, their carcasses washed ashore on beaches and state parks.

Experts at the Marine Mammal Center, the world’s largest marine mammal hospital, said it’s the most gray-whale deaths they have seen in a short span since 2019, when the center performed 13 whale necropsies.

“It’s a lot of whales to have stranded in our small area within a week,” Pádraig Duignan, the center’s director of pathology, told The Washington Post. “We’ve had four whales come out of nowhere – no premonition or warning that this was on the way.”

Duignan said the center may have anticipated an elevated number of whale deaths in his area had many whales been found stranded ashore in Mexico or Southern California as they passed through those regions during the spring migration. There was no such warning, he said.

“If this particular trend continues, that would be extremely worrying,” he said.

An adult female gray whale was found on April 1, another adult female on April 3, and two more – a subadult male and adult female – were found Thursday.


Duignan said it was particularly unfortunate that the deaths included three female whales. “The breeding-age females are really the most important part of the demographic – it’s a shame when they die,” he said.

Scientists at the center suspect that two of the whales died after being struck by ships, and they are investigating the other deaths. Necropsies of the gray whales found two had experienced blunt force trauma after being in “recently good body condition,” Duignan said.

The latest deaths occurred during what federal authorities have declared an unusual mortality event, or UME. Elevated numbers of gray whales have been stranded along the West Coast since the beginning of 2019, according to the National Oceanic and Atmospheric Administration (NOAA). That year, 122 gray whales were found stranded across Alaska, Washington, Oregon and California. Last year, 79 gray whales were found.

As of April 6, 2021, NOAA had tracked eight stranded gray whales this year along the West Coast, including five in California. NOAA Fisheries spokeswoman Kate Goggin said that the agency is aware of the most recent whale deaths and that the tracker will be updated this week.

Even with the drop in the number of stranded gray whales from 2019 to 2020, Goggin said the 2020 count was higher than the annual average in the 18 preceding years.

Duignan said the center, which handles about a 600-mile area along the coast, may see two to three gray whale deaths in a non-UME year.


“Having four in one week should be our entire annual intake,” he said.

The center said that in addition to entanglements involving fishing gear and trauma from ship strikes, malnutrition may be a cause of whale deaths in recent years – prey availability, for one, may be affected by the changing climate and warming water temperatures.

The center said biologists have observed more gray whales in “poor body condition” during their annual migrations since 2019. Duignan said center experts are studying gray whale nutrition and are looking to better understand how much of a role nutrition has played in whale deaths.

Kristen Monsell, oceans legal director at the Center for Biological Diversity, said it is “incredibly alarming and heartbreaking to see this many dead whales in just over a week,” adding that it is “especially so if at least some of the deaths were likely preventable.”

She said whales washed ashore can be “just the tip of the iceberg” because many whales sink when they die.

In January, the advocacy group filed a lawsuit against the U.S. Coast Guard and National Marine Fisheries Service for “failing to properly evaluate the risk to endangered whales in shipping lanes,” Monsell said. As part of the suit, the group is calling for the federal government to consider measures, including mandatory vessel speed limits, to protect whale habitats.


The group also co-sponsored a bill introduced in the California legislature this year that calls for most state-managed trap fisheries to use ropeless fishing gear by November 2025 to better protect whales and other marine species.

Duignan encouraged anyone operating recreational boats or shipping vessels to be aware of the gray whale’s migration patterns.

“Given that we know so many of these whales die because of human interaction, anything from smaller boats up to big shipping containers – the people operating these boats should be aware the whales are migrating now and they’re close to the coast,” he said.

“It’s just a matter of better awareness and not approaching the whales if they’re seen,” he added. “You may see one on the surface, and that could mean another whale is underneath that could be struck.”