Spotting a gray whale in San Francisco Bay can feel like a gift—one minute you’re watching the water, the next you’re holding your breath as a massive body rises and exhales.
But researchers are now spelling out the darker side of those sightings: nearly 1 in 5 gray whales that enter the bay die there.
The new analysis, reported April 13 in Frontiers in Marine Science, is based on 100,000 photos taken between 2018 and 2025. Josephine Slaathaug, a whale biologist at Sonoma State University in Rohnert Park, Calif., and her colleagues used those images to identify 114 individual whales that visited the bay over that stretch of time. In the same region, they documented 70 gray whale carcasses. From that, they matched 21 photo-identified whales—roughly 18 percent—to the carcasses, concluding they died after entering the bay. And, Misryoum newsroom reported, that estimate could be low.
The team points out that many carcasses were too decomposed to be matched using photos. Still, most of the 49 carcasses that remained identifiable enough to assess location were found in or near the bay, which suggests those whales likely died after coming in as well. For a lot of the story, though, it wasn’t just where the whales were found—it was what killed them.
The paper indicates that vessel strikes were a major factor. Among the 21 identified individuals, nine deaths were caused by boat impacts. For the 70 carcasses overall, 30 of the cases where a cause of death could be determined were linked to vessel strikes. It’s a grim math: even when a whale makes it into the bay, the odds of leaving alive may be far from great. “If you’re desperate, and you go into San Francisco Bay, it looks like you’ve got a really, really high chance of not making it back out,” Joshua Stewart, a marine ecologist at Oregon State University in Corvallis, told Misryoum.
There’s also a question researchers can’t ignore: why are the whales showing up there at all. In 2018, researchers noticed that some possibly hungry gray whales began making pit stops in San Francisco Bay to find food. That behavior reportedly lined up with the onset of a large die-off among whales—an event experts attributed to decreased food availability in the Arctic. A similar trend was also described in the late 1990s, as if the pattern keeps returning when conditions tighten.
Stewart cautions against thinking of the bay as a routine feeding stop. Misryoum newsroom reported that gray whales have also been spotted possibly feeding in other unusual areas—off Florida, New England, and Hawaii. In theory, shifting where they feed could make the broader population more resilient to warming seas. But that only works if there’s real protection for the whales in those places, including the bay. Slaathaug argued that feeding in different areas might help, but Stewart framed the behavior more skeptically—“I kind of take the view that it’s more of a desperation option, and it’s really only necessary because they’re not getting what they need in the Arctic.”
On the shore, it’s easy to mistake the spectacle for stability. The waterline smell—salt and diesel, that mix that always seems to cling to harbors—doesn’t change when a whale surfaces, and for a moment it feels like the ocean is doing what it always does. But Misryoum analysis indicates the bay is becoming something else: a place where animals search for food, and sometimes don’t make it back out. And if climate change keeps reshaping migration and feeding, those dangerous detours may become less of an exception and more of a symptom.
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