Why do gray whales keep dying in San Francisco's waters?

Climate change and shifting migration patterns are bringing rare research opportunities and new mysteries.

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The whales have brought wonder, as residents and researchers now get to closely observe how they feed, breed and socially engage. They've also brought growing unease: why are so many of them undernourished and dying?

In 2025, a record number of 21 dead gray whales were found in the broader San Francisco Bay. So far this year, seven have died due to a combination of dwindling prey availability, climate change and human causes, researchers say.

The 4,140-sq-km bay is the largest estuary on the west coast of the US. Before 2018, this species of whales wasn't known to stop seasonally or consistently in the bay, bypassing it on their migration route down to Baja California and back up the Arctic, said Josephine Slaathaug, who led a recent study on gray whale mortality in the bay.

The impressive gray whales have the longest annual migration of any mammal, travelling an approximate 15,000-20,000km roundtrip to breed.