A dead gray whale floats off Cavallo Point in San Francisco Bay on April 3, 2026.
Norely Faz © The Marine Mammal Center, NOAA Permit #26532
Like many gray whales, a young male called Denali likely wintered in the balmy waters off Baja before propelling northward each spring to fill his belly in the Arctic. Marine scientists saw this whale, named after his white spot shaped like Alaska, every year between 2020 and 2024. But last April, partway through his 10,000-mile annual migration, Denali died in San Francisco Bay.
Local scientists from the Marine Mammal Center and California Academy of Sciences, who examined Denali’s body near the Golden Gate Bridge, believe that a vessel probably struck him. In 2025, Denali was one of 21 dead gray whales, a record-high number for the Bay Area.
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The first research to document the fatalities, published in the journal Frontiers in Marine Science on Sunday, found that at least 18% of the gray whales spotted in San Francisco Bay from 2018 to 2025 died. Vessels killed at least 40% of them, and many others starved, the study found.
“This is a really important study because it sets the stage for researchers to go in and understand, almost in real time, a significant change not only in the behavior of this species but also the negative impacts of human activity,” Ari Friedlaender, a UC Santa Cruz ecologist who studies whale migrations but was not involved in this research, told SFGATE.
The new study documents the gray whales’ plight, but elements of the story remain a mystery. And it’s still happening. In 2026, at least six gray whales have already washed up dead in the Bay Area, according to the Marine Mammal Center. (Experts from both the center and the California Academy of Sciences contributed to the new study.)
Between 2018, when gray whales started appearing more regularly in San Francisco Bay, and 2025, experts identified 114 of the sea giants visiting, according to the study. Most came for the first time and didn’t return, with only four appearing across multiple years, the authors report. To compile the numbers on the whales’ different fates in the bay, the researchers used local surveys, photographs and necropsy records.
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“While we found a minimum confirmed mortality rate of 18%, we do have a lot of evidence that would support the actual mortality rate likely being higher, even in the range of between 40% and 50%,” Josephine Slaathaug, a graduate student at Sonoma State University and the lead author of the paper, told SFGATE. “That’s very concerning.”
It’s not just the so-called “bay grays” in trouble.
The Eastern North Pacific population of gray whales, which migrates along the West Coast, faces dramatic declines overall. In 2025, this population of grays fell to just shy of 13,000 whales, the lowest number recorded since the 1970s. The whales are likely struggling to find enough food in the summertime in the Arctic, where climate change is disrupting the ecosystem.
Slaathaug said one theory on why they keep entering the bay is that they’re hungry and looking for food. Malnutrition, leaving the whales weak, might even make it easier for vessels to catch them.
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“We know the gray whales that are dying are in extremely poor nutritional states,” John Calambokidis, a research biologist with Cascadia Research Collective and one of the study authors, told SFGATE. “We know that gray whales that feed elsewhere are not experiencing the same kind of mortality that the larger population that feeds in the Arctic are showing. So all of those things point to this prey-related issue in the Arctic. We also know that the climate change-related factors have been most dramatic in the Arctic.”
The researchers are still working hard to find new ways to protect the gray whales visiting San Francisco Bay. Currently, the initiative Whale Safe assists captains in locating and avoiding the whales, and Blue Whales Blue Skies collaborates with shipping companies to reduce their speeds.
Meanwhile, Slaathaug acknowledged that day after day on the water examining dead whales, many of which she had also watched while they lived, took a toll.
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“On a personal note, it can be very challenging to conduct research on live whales in an area where the death rate is so high,” Slaathaug said.