Gray whales, once rare in San Francisco Bay, dying there at alarming rates | California

Gray whales have always been a rare sight in San Francisco Bay. They travel more than 10,000 miles north from the warm lagoons of Baja California in Mexico to the Arctic region to feast on shrimp-like animals during the summer, rarely stopping in the busy shipping corridor for extended periods.

But in recent years, this story has changed dramatically. A new study, published this week in the journal Frontiers in Marine Science, finds that the bay’s gray whales are dying at an alarming rate, largely due to ship strikes.

Northeast Pacific (ENP) gray whales began appearing more frequently in the busy shipping corridor around 2018. According to researchers, at least 18% of gray whales that entered the bay between 2018 and 2025 died. They determined that for more than 40 percent of whale carcasses, the cause of death was blunt trauma consistent with ship strikes, prompting increased efforts to prevent more fatal collisions.

“It was historically very unusual for them to enter the bay, especially for longer periods of time or consistently year after year,” said Josie Slaathaug, lead author of the study.

There are subgroups of whales known to hunt for food in the southern Arctic, but the majority of whales recently observed feeding in the bay were not part of these feeding groups.

No wave of new whales has been observed in the waters since the late 1990s, according to Slaathaug. Then and now, researchers theorize that warming in the Arctic is disrupting the availability of food for whales, causing them to hunt in new places such as the bay, although it’s unclear what exactly they might eat there.

Their potential new feeding spot, however, constitutes a major shipping lane.

The true death rate for whales in the bay could be higher, hovering between 40 and 50 percent, Slaathaug said. It’s difficult to match photographs of live whales with those of dead animals, because of the carcass or lost carcass, she said.

In recent years, there have been several reports of dead whales washing up on Bay Area beaches. The ENP gray whale population is declining due to malnutrition and starvation from climate-induced prey shifts in the Arctic, according to Slaathaug. The Southwest Fisheries Science Center estimated a total population of about 13,000 whales, its lowest number since 1970.

“It’s not unique to their migratory corridor that many whales are dying,” Slaathaug said. “What’s unique about the San Francisco Bay Area and this study is that there was such a clear emerging cause of death.”

Some local efforts are underway to reduce vessel collisions.

The Marine Mammal Center, affiliated with the study, developed a program called Whale Smart, to teach San Francisco Bay vessel operators how to interpret whale behavior to avoid close encounters.

In Alaska, where ships also pose a threat to the whale population, a fleet company has partnered with WhaleSpotter, a company that uses AI and thermal imaging to detect the presence of whales, so they can change course well in advance.

Last year, the Center for Biological Diversity, a conservation group, sued the U.S. Coast Guard, which regulates shipping off California’s coast, for failing to analyze how ship routes can harm whales and sea turtles.

“This most recent study on gray whales reaffirms that we have vastly underestimated the problem and are not managing human activities well enough to keep the whales out,” said Catherine Kilduff, the center’s senior attorney.

Federal action is needed to reduce the number of fatal crashes, Kilduff said.

Under the Endangered Species Act, she said, the Coast Guard would have to consult with the National Marine Fisheries Service, the government agency responsible for protecting the country’s ocean life and habitats, when defining shipping lanes to assess the impact on marine wildlife, Kilduff said.

The Coast Guard did not immediately respond to a request for comment on the study’s findings.

Kilduff also suggested mandatory speed limits for ships. “There are voluntary speed reductions on the West Coast, but there is evidence that these reductions are not effective. The compliance rate is not high enough,” she said.

A 2022 study co-authored by the National Oceanic and Atmospheric Administration found that average speeds of large ships declined from 2010 to 2019 in voluntary speed reduction zones. But the researchers determined that the cooperation rate of about 50 percent was below the amount needed to reduce mortality from ship strikes to a level that would maintain a sustainable whale population.

“These whales use the oceans in such sophisticated ways. We can learn a lot from them, and if we can find ways to avoid killing them, I know they will return to healthy population levels,” Kilduff said.