Why are gray whales dying in San Francisco's waters? US scientists search for clues

California's blustery San Francisco Bay is home to the Golden Gate Bridge, commercial ports, public marinas and ferry boats. But more recently, a new sight is attracting locals' attention: Eastern North Pacific gray whales.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."It's a new habitat that they've chosen to utilise," the graduate student at Sonoma State University and the lead author of the paper tells the BBC, noting years of steep declines in their prey in the Arctic.Many of those that turned up in the bay are adult and juvenile males that are heading to the Arctic. Notably, the whales observed are skinnier than they normally would be at this time of year, Slaathaug and several other researchers tell the BBC.