Scientists are investigating a rise in gray whale deaths in San Francisco Bay, where the species was not previously known to gather seasonally.
Gray whales are dying in higher numbers in San Francisco Bay
Since 2018, researchers have observed gray whales entering the 4,140-square-kilometer bay during migration, a behavior not seen before, according to Josephine Slaathaug, who led a recent study on mortality in the area. The bay, the largest estuary on the U.S. West Coast, was typically bypassed by whales traveling between Baja California and the Arctic. Now, their presence coincides with increased strandings and deaths, prompting urgent study into the causes.
Scientists are examining environmental and human factors behind the deaths
Possible causes under review include ship strikes, entanglement in fishing gear, changes in prey availability due to warming waters, and exposure to pollutants. Slaathaug noted that the shift in whale behavior may reflect broader ecosystem changes affecting migration patterns. No single cause has been confirmed, but researchers are collecting data from necropsies, sightings, and environmental monitoring to identify trends.
Researchers say understanding the shift is key to preventing further losses
Officials from the National Oceanic and Atmospheric Administration and local marine institutes are collaborating on the investigation. They emphasize that determining why whales are now using the bay — and whether it poses a risk — will inform conservation strategies. Continued monitoring is planned to assess whether the behavior is temporary or signals a lasting change in gray whale migration.
Why weren’t gray whales previously seen in San Francisco Bay?
Before 2018, gray whales migrated past the bay without stopping, traveling directly between their feeding grounds in the Arctic and breeding lagoons in Baja California.
What could be causing the increase in whale deaths?
Scientists are looking at ship strikes, fishing gear entanglement, changes in food supply due to ocean warming, and pollution as potential factors, though no definitive cause has been identified yet.
