Gray Whale Mortality Skyrockets in San Francisco Bay Amid Shipping Hazards
Gray whales, once a rare spectacle in the San Francisco Bay, are now perishing there at alarming rates, according to a groundbreaking study published this week in the journal Frontiers in Marine Science. Researchers have documented a sharp increase in whale deaths in the bay, primarily attributed to collisions with vessels along this bustling shipping corridor.
Historical Rarity Turns to Tragic Trend
Historically, gray whales have been infrequent visitors to the San Francisco Bay. These majestic creatures embark on an epic migration, traveling over 10,000 miles from the warm lagoons of Mexico's Baja California to the Arctic region to feed on shrimp-like animals during summer months, typically avoiding prolonged stays in busy maritime routes. However, since around 2018, Eastern North Pacific (ENP) gray whales have appeared with greater frequency in the bay, leading to a dire shift in their fate.
The study reveals that at least 18% of gray whales entering the bay from 2018 to 2025 have died. For more than 40% of the whale carcasses examined, the cause of death was blunt force trauma consistent with vessel strikes. Josie Slaathaug, lead author of the study, noted, "It was historically very unusual for them to enter the bay, especially for longer amounts of time or consistently year after year."
Climate Change and Foraging Shifts Drive Whales into Danger
Researchers theorize that Arctic warming is disrupting food availability for gray whales, compelling them to seek new foraging grounds such as the San Francisco Bay. While it remains unclear what exactly they are eating there, this potential new feeding area coincides with a major shipping route, heightening the risk of fatal encounters. Slaathaug explained that the true mortality rate in the bay may be as high as 40% to 50%, though tracking is challenging due to skin decay or lost carcasses.
The ENP gray whale population has been declining due to malnutrition and starvation from climate-driven prey shifts in the Arctic. The Southwest Fisheries Science Center estimates the population at about 13,000 whales, the lowest count since 1970. Slaathaug emphasized, "It's not unique to their migratory corridor that a lot of whales are dying. What is unique about San Francisco Bay and this study was that there was such a clear emerging cause of death."
Conservation Efforts and Legal Actions Underway
In response to the crisis, local initiatives are emerging to mitigate vessel collisions. The Marine Mammal Center, affiliated with the study, has launched the Whale Smart program, educating vessel operators in the San Francisco Bay on interpreting whale behavior to avoid close encounters. In Alaska, a fleet company has partnered with WhaleSpotter, utilizing AI and thermal imaging to detect whales and alter course proactively.
Last year, the Center for Biological Diversity sued the US Coast Guard for failing to analyze how vessel routes may harm whales and sea turtles. Catherine Kilduff, senior attorney at the center, stated, "This most recent study about the gray whales reaffirms that we have way underestimated the problem and we are not managing human activities well enough to avoid the whales." She called for federal action, including mandatory speed limits, as voluntary measures have proven insufficient.
A 2022 study co-authored by the National Oceanic and Atmospheric Administration found that while average vessel speeds decreased in voluntary reduction zones from 2010 to 2019, the cooperation rate of about 50% is inadequate to reduce strike-related mortality to sustainable levels. Kilduff concluded, "These whales are using the oceans in such a sophisticated way. We can learn so much from them, and if we can figure out ways to avoid killing them, I know that they'll come back to healthy population levels."
