As oceans change, gray whales enter riskier waters
A Sonoma State graduate student is studying how climate-driven shifts are bringing gray whales into San Francisco Bay — and into danger from vessel strikes
Josephine Slaathaug grew up in South Dakota, one of the most landlocked states in the country, where her early experience with animals came on a cattle ranch. Today, she studies gray whales in San Francisco Bay — an unlikely place for them to be.
Since 2018, gray whales have been appearing seasonally in the bay, a shift that has drawn attention from scientists and the public alike. The whales, part of the Eastern North Pacific population, typically migrate thousands of miles between Arctic feeding grounds and breeding lagoons in Baja California. Their presence in San Francisco Bay represents a departure from that well-established pattern.
Gray whales are among the most visible marine mammals along the California coast. “Gray whales are an extremely accessible species for most Californians,” Slaathaug said. “They complete this yearly migration all along the California coast, very close to the shoreline. Many Californians have seen gray whales or learned a lot about gray whales growing up.”
Slaathaug, a master’s student in biology at Sonoma State University, led the research investigating what’s behind the recent change in gray whale migration and what it means for the whales’ survival.
The findings point to a clear and concerning pattern.
Using photo-identification to track individual whales, Slaathaug and a team of researchers documented 114 animals entering the bay between 2018 and 2025. Several were later matched to gray whale carcasses, revealing a minimum mortality rate of 18 percent. In many cases, cause-of-death indicators were consistent with injuries that would be caused by a vessel strike.
“Gray whales are entering the bay, likely pressured by climate changes and decline of their prey in the Arctic,” Slaathaug said. “And while they are here utilizing this new habitat, they are facing a lot of human-caused mortality because they have no protective measures for them in place.”
The pattern points to a difficult reality: The same behavioral flexibility that allows gray whales to respond to environmental change — in this case, finding food in the relatively new geography of San Francisco Bay — might also be placing them at greater risk.
The research, published in the journal Frontiers in Marine Science, has drawn widespread attention, with coverage from a diverse variety of media outlets including The San Francisco Chronicle, The New York Times, The Guardian, and People.
The work resonates beyond the scientific community, particularly in a region with strong environmental awareness. “A lot of people in this community deeply care about the environment around them, and deeply care about conservation and climate change,” Slaathaug said. “This work is kind of an intersection of a few of those big topics.”
She did not grow up around oceans, but she grew up closely attuned to the natural environment. “I was always outdoors,” she said. Life on a cattle ranch instilled a habit of close observation of animals and of the landscapes and conditions around them, an attentiveness carries into her current work.
At Northeastern University as an undergraduate, a cooperative education program placed Slaathaug in the field with the Sarasota Dolphin Research Program, where her focus narrowed. She describes herself as “a bit one-track mind on the cetacean front.”
In 2023, she moved to California to intern at the Marine Mammal Center in Sausalito. There, she began building a photo-identification catalog of gray whales entering San Francisco Bay — work supported by a National Science Foundation Graduate Research Fellowship.
That catalog has become the backbone of her research. Drawing on photographs, necropsy findings, and documentation of gray whale strandings, Slaathaug tracks individual whales over time to better understand how climate-driven changes are affecting their health and survival.
She chose to pursue her graduate studies at Sonoma State University for its emphasis on research. She described the biology department as a “research-forward department,” one that supports students in carrying projects through to publication even before graduation. That environment, she said, has been critical to advancing her work.
She credits her faculty advisor and research co-author, Dr. Daniel Crocker, as a key supporter who helped shape the project and guide it from fieldwork to peer-reviewed publication. She added that multiple faculty members in the biology department have supported her work.
Mentor and study co-author Moe Flannery at the California Academy of Sciences, known for her work in the Marine Mammal Stranding Network and expertise in necropsy and specimen curation, also helped shape Slaathaug’s approach. Together, their field observations and post-mortem data create a more complete picture of what is happening to whales at the boundary between a changing ocean and an urbanized coastline.
What is emerging is a pattern that is still unfolding: Gray whales are adapting to a shifting climate in real time. But in places like San Francisco Bay, adaptation may be leading them into conditions they are not equipped to survive.
Slaathaug hopes the research will serve as “foundational knowledge” to inform policy responses as gray whales continue to enter the bay. In other regions, including Boston Harbor, parts of Canada, and areas near New York, seasonal slow-speed zones have been shown to reduce vessel strikes, offering potential models for protection in San Francisco.
In addition to primary funding from the National Science Foundation’s Graduate Research Fellowship Program (DGE-2437852), the research was financially supported by The California State University Council on Ocean Affairs, Science, and Technology.
Slaathaug plans to continue her work as a PhD candidate at Oregon State University in the fall. As gray whales continue to enter San Francisco Bay, her research offers a foundation for how scientists and policymakers might respond, providing the data needed to anticipate risk, test interventions, and adjust human activity to better protect a species adapting to a changing climate.