In just a week and a half, four whales were found dead in the San Francisco Bay Area, sparking concern among marine biologists and conservationists. What’s behind this sudden cluster of whale deaths? Here’s what experts are saying.
4 Whales Found Dead in 10 Days: What Happened?
On April 8, a juvenile minke whale beached itself near Emeryville after spending nearly a week swimming in San Francisco Bay. Although initially appearing healthy, experts later found signs of illness and made the difficult decision to euthanize the whale.
This tragic event marked the fourth whale death in less than two weeks in the region. The other three victims were gray whales:
- March 30: A 36-foot female gray whale was found dead at Black Sands Beach in Marin Headlands. Cause of death: unknown.
- April 2: A male gray whale was discovered floating near Angel Island. Cause of death: unknown.
- April 4: A subadult male gray whale washed ashore at Fort Point Rock Beach. Cause of death: likely a vessel strike, according to the Marine Mammal Center.
Is This an “Unusual Mortality Event”?
The recent whale strandings have raised concerns about a possible Unusual Mortality Event (UME)—a term used when marine mammals die in abnormally high numbers.
“This situation feels familiar,” said Kathi George, Director of Cetacean Conservation Biology at the Marine Mammal Center. “It reminds me of a few years back when we experienced a spike in whale deaths.”
However, scientists also caution that while the recent strandings are alarming, they are not yet statistically unusual for this time of year.
Migration Season: Why Whales Are in the Bay
According to Moe Flannery of the California Academy of Sciences, April and May are peak months for gray whale migration. These whales travel from their breeding grounds in Mexico to feeding areas in Alaska, often passing through or stopping in San Francisco Bay.
“Although it seems like a lot of deaths in a short period, the overall number of stranded whales isn’t significantly different from previous years,” Flannery explained.
Whales are exposed to various threats during migration, including malnutrition, disease, and collisions with ships.
Why Are Whales Entering the Bay More Often?
Whales were rarely seen inside the bay until around 2016, when they began appearing more frequently. Scientists believe whales may be:
- Searching for food after expending energy during mating and nursing.
- Resting in the bay as a stopover during their long migration.
- Responding to climate change, shifting prey locations, and warming ocean waters.
George explains that gray whales do not feed during their time in Mexico and often arrive in California underweight or malnourished. This weak condition makes them more vulnerable to human-related threats.
Climate Change and Whale Health: A Bigger Picture
Between 2019 and 2023, gray whales experienced a documented population decline of over 40%, prompting NOAA Fisheries to declare an unusual mortality event. During that time, 347 gray whales stranded along U.S. coastlines.
“They left the Arctic with a half tank,” said Giancarlo Rulli of the Marine Mammal Center. “Due to climate change, their usual high-nutrition feeding grounds moved farther away, forcing them to forage on lower-quality food.”
This pattern of malnourished whales continues to be a major concern among marine scientists.
What’s Next? Ongoing Monitoring and Public Awareness
So far in 2025, seven dead gray whales have been reported along the California coast. Scientists emphasize that it’s too early to confirm whether we’re entering a new unusual mortality event.
“We’re still analyzing the data,” George noted. “It’s essential to look at the entire migration range to understand what’s happening.”
The Marine Mammal Center has already documented 18 individual whale sightings in the bay this year, with most reports coming from areas east of Angel Island.
What You Can Do: Boater Safety and Whale Conservation
As whales continue migrating through the bay until mid-May, experts urge boaters and watercraft users to stay vigilant and avoid disturbing marine wildlife.
“We all share this environment,” Flannery said. “Awareness is key to protecting these incredible animals.”