Gray whales undertake one of the longest annual migrations of any mammal on Earth. They spend the summers feeding in the nutrient-rich waters of the Arctic before traveling about 12,000 miles round trip to winter in the warm and protected lagoons of Baja Mexico. But as ocean conditions change, some gray whales are taking unexpected detours.
In recent years, gray whales have been spotted feeding in unusual places, including busy San Francisco Bay. A new study led by researchers at Sonoma State University in California found something troubling: 18% of gray whales that enter San Francisco Bay die there.
Gray whales are especially vulnerable to vessel strikes because they ride low in the water and can be hard to see, especially in the Bay’s frequent fog. At the same time, the Golden Gate Strait funnels both ships and whales through a narrow and heavily-trafficked passage.
According to the study, which was recently published in the journal Frontiers in Marine Science, climate change may be driving this behavior. Warming Arctic waters are disrupting the whales’ food supply, and the population has dropped by more than half since 2016. Instead of fasting during migration, some whales appear to be using the Bay as an emergency pit stop for food.
But the strategy is dangerous. Between 2018 and 2025, 70 so-called “Bay Grays” were found dead - 30 from vessel strikes. Many others showed signs of malnutrition.
Researchers say measures like ship speed limits and route changes could reduce collisions. As gray whales adapt to a changing ocean, reducing human-related risks could help more of them survive the journey.
