As the climate changes, many marine animals are on the move: shifting their usual locations as they try to find food or more suitable habitats. Sometimes, this puts them in harm’s way as they travel into regions busy with human activity.
Now, scientists are sounding the alarm that gray whales might be in trouble for this very reason.
According to a new study published in Frontiers in Marine Science, gray whales have started travelling into San Francisco Bay and 18 per cent of those that do end up dead – often killed after being hit by fast-moving boats.
The Eastern North Pacific population of gray whales make long migrations from the Arctic, where they feed, to the tropical lagoons of Baja Mexico to have their calves. They don’t usually eat on the journey from one to the other. But this is changing.
As the Arctic warms, it’s impacting the whales’ prey and, in turn, the gray whales themselves.
“Some individuals have adapted to forage in habitats south of the traditional Arctic feeding grounds,” write the authors in the study.
These enormous animals didn’t used to visit California’s San Francisco Bay – not until 2018. Now they’re being seen there, and scientists are worried. These waters are known for their intense boat traffic.
“San Francisco Bay is a highly trafficked waterway, and the Golden Gate Strait serves as a bottleneck through which all traffic and whales must enter and exit,” says lead author Josephine Slaathaug of Sonoma State University in a statement.
When these baleen whales come up to breathe, it’s incredibly hard for boats to spot them – putting them at risk of getting hit by vessels. “Gray whales have a low profile to the water when they surface, and this makes them difficult to see in conditions like fog which are common to San Francisco Bay,” she adds.
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The researchers created a catalogue of whales using photos by citizen scientists and opportunistic surveys from 2018 to 2023 along with systematic surveys from 2023 to 2025.
According to their paper, at least 114 individuals have visited San Francisco Bay between 2018 and 2025. Only four of those were seen in the bay again.
They compared the individuals with necropsies (animal autopsies) of 70 gray whales that were found dead during the same time: 45 were identifiable and 21 of those could be matched to the researchers’ catalogue.
“At least 18 percent of the individuals identified in San Francisco Bay later died in the area,” says co-author Bekah Lane of the Center for Coastal Studies. “Our broader analysis of local strandings both inside and outside San Francisco Bay found that over 40 per cent of these whales died of trauma from vessels.”
Malnutrition was identified as another cause of death.
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The researchers want more studies to help them get to the bottom of what’s going on. “These results are an important piece of the larger puzzle of what is going on in the overall population as they attempt to adapt to climate change in real time,” says Slaathaug.
If they can learn more about what’s happening, it will help them find ways to protect gray whales. “Protecting this population along its migratory corridor as it contends with a changing environment will be critical for the species’ ability to rebound from its current decline,” write the study authors.
Top image: Satellite view of San Francisco Bay. Credit: Satellite Earth Art/Getty Images
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