California’s windy San Francisco Bay features the famous Golden Gate Bridge, commercial ports, public marinas and ferries. But more recently, a new presence is catching the attention of locals: the gray whales of the Eastern North Pacific.
The whales have raised eyebrows, as residents and researchers can now observe up close how they feed, reproduce and interact. They have also generated growing concern: why are so many of them malnourished and dying?
In 2025 there were a record number of 21 gray whales killed in San Francisco Bay. So far this year, seven have died.
The 4,140 km² bay is the largest estuary on the U.S. west coast. Before 2018, this species of whale was not known to seasonally or routinely stop in the bay, but instead avoided it on its migratory route to Baja California, Mexico, and back to the Arctic, according to Josephine Slaathaug, who led a recent study on gray whale mortality in the bay.
The impressive gray whales have the longest annual migration of any mammal, traveling approximately 15,000 to 20,000 km round trip to breed.
“It is a new habitat that they have chosen to use,” the Sonoma State University graduate student and popular author of the article explains to the BBC, pointing out the years of sharp decline in their prey in the Arctic.
Many of those that have appeared in the bay are adult males and juveniles heading to the Arctic. It should be noted that the whales observed are thinner than would be fashionable at this time of year, as Slaathaug and other researchers explain to the BBC.
“They do not have the energy reserves necessary to complete the entire migration back to the Arctic, so hunger may push them into the bay,” he said.
Dead or dying gray whales have also turned up in Washington state and Oregon. Although they were not included in Slaathaug’s study, researchers believe changes in their behavior could be related.
Several factors to observe
While a lack of food may be driving the whales into the bay, it is not necessarily starvation that is killing them. In recent years, nearly a fifth of the gray whales that have swam into San Francisco Bay have died there, usually after being struck by ships, according to Slaathaug’s study published in the journal Frontiers in Marine Science.
Slaathaug’s study examined hundreds of photographs of whales and carcasses found in the bay since 2018. His team described “a very concerning mortality rate in San Francisco Bay” that continued to increase in 2025, with whales in the bay highly susceptible to ship strikes.
Still, researchers say the factors causing these deaths are worth exploring. The bay offers a unique opportunity to better understand migration patterns and how climate change is changing routes and food supplies.
“It’s sad to see a dead whale. It’s even sadder to see a dead whale that you may have recognized from studying it. But there’s also a lot we can learn,” said Kathi George, whose team helped Slaathaug with his research and several necropsies.
Whales, he said, may be harbingers of larger changes beneath the ocean’s surface.
The fact that whale sightings and strandings have started earlier than usual this season – starting with two in January, when the peak usually occurs in April – is a cause for concern, as it indicates that these creatures are in more trouble than initially thought.
Slaathaug and his colleagues have also observed very low numbers of offspring, indicating a low birth rate. That could mean that this population is not recovering or rebounding as it has in previous times of population decline.
“That, along with the high human-caused mortality rate in this area, is really leading scientists to be concerned and looking for ways to find solutions,” Slaathaug said.
Moe Flannery, co-author of the study, told the BBC that this is the first time in decades that the problem seems imminent. He says scientists are learning how to make waters from Alaska to Mexico safer for whales.
A population in crisis
The population of gray whales that inhabit the west coast of North America is not considered endangered. However, their number has fallen from 27,000 in 2016 to 12,500 in 2025, a decline that the US National Oceanic and Atmospheric Administration has called an “unusual mortality event.”
“This is an immediate crisis that must be addressed, and this paper is just the first step in collecting the necessary scientific data to inform the conservation and management of this endangered species,” Flannery said.
That danger also becomes imminent for humans when a gray whale weighing between 30 and 40 tons begins to float in the bay, as happened earlier this year. The U.S. Army Corps of Engineers towed the body to a secluded beach for George and his team to perform a necropsy.
But, in an unusual turn of events, George explained that his team had not yet reached the first whale when they received a call about a second that required immediate attention.
“Unfortunately, we had nowhere to put the whale, so it floated out of the bay,” he said.
The bay’s waters are somewhat enclosed and relatively congested by large container ships, ferries and public marinas, increasing the chance that a whale – dead or alive – will collide with a vessel.
There is an urgency to “get these whales out of the shipping lanes as soon as possible,” said Gary Reed, director of marine traffic for the U.S. Coast Guard in San Francisco, who is working with George and a coalition of industries to keep the port safe for whales and other wildlife.
The Coast Guard and ferry companies have implemented safety measures and captains are being trained to give the whales space, slow down and report sightings. Reed hopes to soon install an infrared camera on Angel Island to monitor whales surfacing at night and in high-traffic areas.
“We are willing to try anything we can think of, see what works,” he said.
Gray whales have made incredible recoveries before, most notably when the United States ended commercial hunting and introduced the Marine Mammal Protection Act in the early 1970s, said Michelle Barbieri Lino, a wildlife veterinarian who was not part of the study.
“They are a species that makes us feel awe at how these animals can recover from stressors and shock,” he said, noting that gray whales are intelligent creatures that are probably trying out the bay as “a place to have a snack” on their long journey back to the Arctic.
This, he said, offers a ray of hope.
“If they have the protections they need in San Francisco Bay, this could be a place where they can successfully create a new feeding stop that helps them complete their migration, come back again and thrive,” Lino said.
Keep reading:
* Third dead whale in less than a month alarms New York
* 2nd dead whale found in NJ and concern grows over boat strikes
* Whale dies after colliding with boat in New Jersey
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