Five whales have died in San Francisco Bay in the last month. The deaths of four gray whales around the bay and the beaching and eventual euthanizing of a minke whale are being investigated by the Marine Mammal Center and the California Academy of Sciences.
Necropsies of four of the whales have indicated that one died due to a probable vessel strike, but the causes of death for the others have yet to be determined. Scientists were able to collect samples from the other carcasses for further analysis. The five whales were found all around the bay: Alameda, Emeryville, Muir Beach, Angel Island and Fort Point.
The recent deaths have raised concerns among scientists and the whale-loving community, what with populations still recovering from an unusual mortality event that took place between 2018 and 2023, where 690 gray whales were stranded along the Pacific coastline.
“They often are addressed and looked at as a sentinel for ocean health,” said Giancarlo Rulli, associate director of public relations for the Marine Mammal Center. “When there’s problems or a mass stranding event for these animals, or they’re showcasing signs of malnutrition or otherwise, it should be noted. We should be paying attention.”
Gray whales take on a great migration throughout the year, traveling from their breeding grounds in Baja California, Mexico, to feed in the Arctic and back. While a handful of whales normally show up in San Francisco Bay in the spring, the number of whales that have been spotted this year is “quite stark,” Rulli said. There are about 10 whale sightings on a given day.
In the past unusual mortality event, possible culprits included a reduction in food sources due to melting ice and warmer temperatures in the Arctic due to climate change.
“These gray whales had basically left the Arctic on their migration in 2019 with a half tank,” Rulli said. “In recent years, we have seen some individuals turn into the bay, and we’ve even documented gray whales actively foraging in the bay. But the San Francisco Bay is not a location where a marine mammal of that size can sustain itself long term. So it very much remains to be seen in the years ahead what happens with the gray whale.”
Scientists are still working to understand why the bay is seeing such an increase in whales this year. Rulli said this year stands out because of the sheer amount of communication among scientists, citizens, and the maritime sector. Rulli credited this to the presence of the Harbor Safety Committee, a collection of local mariners, officials, and nonprofit representatives. He also encouraged citizens to download Whale Alert to help track sightings and reduce the chances of vessel strikes.
Rulli noted gray whales are a resilient species and have bounced back from mortality events in the past. Still, Ben Grundy, oceans campaigner for the Center for Biological Diversity, said that there is more work to be done to protect whales and other marine species in the bay.
Grundy works in the oceans program for the center with a specific focus on protecting whales and other species from vessel strikes and fishing gear entanglement. Roughly 20,000 whales die each year globally from vessel strikes, with an estimated 80 of those happening off the West Coast of the United States. A staggering 300,000 whales and dolphins die globally due to entanglements or accidental capture in fishing gear. And according to scientists, those numbers may be an underestimate.
“We’re only seeing what actually gets reported when whales are washing ashore,” said Grundy. “We know that whales can be hit and sort of just sink to the bottom of the ocean and not be seen or documented or accounted for. So it really is a difficult problem to track.”
Grundy describes these deaths as “truly heartbreaking.” For him and other researchers, these deaths might’ve been prevented if proper regulatory action had been taken. The Center for Biological Diversity is working on campaigns focused on lower shipping speeds in the bay and removing certain fishing equipment, such as consistent vertical lines, that present persistent problems for marine life. Grundy said that regulation can often be reactive, and he encouraged people who are passionate about this issue to advocate for marine life with their local representatives. Recently both the cities of Alameda and Berkeley passed resolutions pledging to support safe passage for marine life in their waters.
Whales are a keystone species for the bay’s unique ecosystem. By protecting these large marine mammals, Grundy said, we can protect the health of the entire bay. He added that, while protecting whales and thus maintaining the unique biodiversity in the estuary is important as an ecological matter, it also fulfills an almost spiritual need for people.
“Whether or not you’re someone who lives close to the water or you’re hundreds of miles inland,” Grundy said, “being able to see and know that there’s this really beautiful or charismatic species out there gives people a sense of connection to the water.”
