Why are gray whales dying in San Francisco Bay?

Gray whale deaths in San Francisco Bay

Scientists report that nearly 18% of gray whales that enter San Francisco Bay die there, a level that stands out as the whales use the region as a foraging area during a shifting climate.

The work ties the growing mortality to multiple pressures that appear to be converging in the bay. Researchers describe climate change as a likely driver of behavioral change—whales are being sighted foraging in unexpected places as traditional Arctic and migration-season food patterns become less predictable. That creates more whale-bay interactions, increasing the chance that animals will encounter additional hazards.

A second factor highlighted is human activity, particularly the risk of vessel strikes. As whales spend more time in the bay, the chance of collision rises. That matters because gray whales are large and mobile, but the bay is also heavily used by ships, ferry traffic, and other marine operations.

The findings effectively reframe the bay from a relatively benign stopover into a potentially dangerous “pit stop.” The combination of climate-driven shifts in where whales search for food and the physical hazards posed by boats could explain why deaths are occurring at rates higher than expected.

Why it matters

This is both a conservation and a management problem. If climate change continues to alter where prey is available, whale exposure to local threats may increase even without changes in whale behavior. That would mean mitigation efforts—such as reducing strike risk where whales concentrate—could become more important over time.

The study also underscores a broader point: ocean ecosystems can respond to climate stress not only by shifting habitats of prey species, but also by changing migration and foraging routes for top marine mammals. When those routes intersect with human infrastructure, mortality risks can climb quickly.