A beached gray whale in Kirby Cove, San Francisco, on May 28, 2025. Six whales have washed up in the San Francisco Bay this week alone, in a year with unusually high whale sightings for the Bay Area’s coast. (Courtesy of Marjorie Cox/Marine Mammal Center)
Six gray whales were found dead in the San Francisco Bay this past week, and researchers are struggling to figure out why.
The recent fatalities bring the total number of whale deaths this year up to 15, according to the California Academy of Sciences. It’s the highest number of whale deaths to occur in a single year since unusual mortality events — strandings that lead to a spate of marine mammal deaths — in 2019 and 2021, which had 14 and 15 fatalities respectively.
“It is a complex, dynamic and evolving situation that’s unfolding,” said Giancarlo Rulli, a spokesperson for the Marine Mammal Center in Sausalito. “What we have seen this year is a massive uptick in both the number of sightings as well as the number of strandings.”
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Rulli noted that while scientists are not yet classifying this year’s high number of deaths as an unusual mortality event, there’s still cause to be concerned.
The first of the six deaths to occur this month was a yearling gray whale that was found near Bolinas on May 21. It was soon followed up by the deaths of two more gray whales — one adult and one subadult — on May 22 and 24, in Fisherman’s Bay, off Southeast Farallon Island, and in Berkeley, respectively.
Marine experts prepare for a necropsy after a gray whale is found dead in Bolinas on May 23, 2025. (Courtesy of Shalina Peterson/California Academy of Sciences)
Two additional adult whales were found on May 26 at Point Bonita in the Marin Headlands and Alcatraz. A final whale death was reported Wednesday night near Alamir Falls in Point Reyes National Seashore, according to CalAcademy.
Researchers have been unable to determine the exact cause of death for any of the whales. The location of the strandings and the state of decay have made it difficult for experts to perform necropsies, or animal autopsies, Rulli said. Some of the whales are lodged underneath docks or are stranded by cliffsides, making them extremely difficult for people to access. Sometimes the whales have already started to decompose and are too degraded to be thoroughly examined.
Of the six that died this week, researchers suspect that at least three of the deaths were caused by vessel or boat collisions. Another gray whale that died in April was also suspected to have died from a collision. It was found with six fractured vertebrae.
Experts are working with the San Francisco Harbor Safety Committee and local ferries to figure out how to safely navigate areas occupied by whales. Part of the solution could be changing routes during whale season based on where the animals are typically observed, Rulli said.
“There are a lot of added threats within the bay,” Rulli said. “You have a large number of whales accessing a very enclosed body of water with large mariner vessels of many types … Keeping whales safe while they are here, typically from late February to beginning of March for gray whales, is something that experts here at the Marine Mammal Center are working really closely on.”
It’s been a weird year for conservationists and whale experts in the bay.
More than 30 individual gray whales have been spotted in Bay Area waters this year, compared to the four seen in all of 2024, Rulli said. Roughly one-third of the whales have stayed in the bay for nearly a month, and it is expected that they will remain in the area for one or two more weeks before continuing their northward migration.
A subadult gray whale is found dead in Berkeley on May 24, 2025. (Courtesy of Kate High/California Academy of Sciences)
While some of the whales are in good condition, others show signs of being malnourished or emaciated, Rulli said. Their behaviors also differ from one another, making it hard for researchers to determine what’s going on during this migration season, he added.
Rulli encouraged members of the public to report any whale sightings in the San Francisco Bay by using the Whale Alert app or through the Marine Mammal Center’s website.
