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

Gray whales are increasingly present in San Francisco Bay, but scientists are concerned about a rising number of deaths. A record 21 dead gray whales were found in the broader San Francisco Bay in 2023, and seven have died so far this year. Researchers believe dwindling prey in the Arctic, climate change, and human activity are contributing factors. Before 2018, gray whales were not known to consistently stop in the bay during their annual 15,000-20,000km migration. Many of the whales observed in the bay are adult and juvenile males heading to the Arctic, and they appear skinnier than usual, prompting further investigation into the cause of these deaths.

A recent study reveals that gray whales are dying at alarming rates in the San Francisco Bay, a location where they were once rarely seen. Since 2018, an increasing number of Eastern North Pacific gray whales have entered the bay, likely due to climate change disrupting their Arctic feeding grounds. Researchers estimate that at least 18% of these whales have died, with over 40% of those deaths attributed to blunt force trauma consistent with vessel strikes. The true mortality rate may be as high as 50% due to difficulties in identifying deceased whales. This concerning trend coincides with a decline in the overall ENP gray whale population, prompting calls for increased efforts to prevent fatal collisions in the busy shipping corridor.