SAN FRANCISCO — Five gray whales have died in and around the San Francisco Bay over the past week, bringing the total number of whales that have washed up this year to 14, according to the California Academy of Sciences.

This marks the highest number of dead whales to have stranded since the unusual mortality event that saw an influx of whale deaths in 2019 and 2021, CalAcademy said. These strandings follow a similar influx of whale deaths in early April when three gray whales and one minke whale washed up around the bay over a week and a half span.

“It indicates something odd is happening,” said Sue Pemberton, the associate manager of marine mammal stranding at CalAcademy. “It’s a very large picture that we’re trying to fill in right now, and the team between the California Academy of Sciences and the Marine Mammal Center are really running hard and running ragged to try and stay on top of what information is available.”

The five whales washed up between May 21 and 26. The first, a yearling gray whale, washed up in Bolinas, in Marin County, on May 21. A partial necropsy that was conducted May 23 was inconclusive and the whale’s cause of death remains unknown, CalAcademy said.

A gray whale washed up May 22 in Fisherman’s Bay off Southeast Farallon Island, and a subadult female gray whale washed up May 24 in Berkeley. Necropsies were not performed on either whale and their causes of death remain undetermined, CalAcademy added.

On May 26, two additional gray whales stranded, CalAcademy said. One gray whale was located at Point Bonita. A suspected gray whale also washed up at Alcatraz. Both animals’ causes of death are undetermined.

Scientists were unable to complete necropsies in some cases due to the inaccessible locations of the whales, a lack of locations to tow whales to for studying and decomposition causing poor tissue quality, CalAcademy said. A necropsy was conducted Wednesday at Kirby Cove in the Marin Headlands on a whale that scientists presume was one of the two whales first sighted on May 26.

CalAcademy and the Marine Mammal Center have not responded to this many strandings in one year since 2021, when 15 whales stranded; fourteen animals died in 2019. The influx of whale deaths was part of an unusual mortality event, in which 690 whales stranded along the West Coast between 2018 and 2023 due to ecosystem changes in their feeding grounds, according to the National Oceanic and Atmospheric Administration.

In a normal year, there are between two and four whale strandings around the San Francisco Bay, Pemberton said.

The event caused a 45% decrease in the eastern North Pacific gray whale population, leaving the species’ long-term prospects uncertain, CalAcademy said. Scientists in Southern California reported record-low gray whale calf numbers this year, and scientists between the United States, Mexico and Canada are continuing to monitor the health of the whale population.

One probable contributor to the influx in strandings is an increased number of gray whales swimming into the bay, Pemberton said. With large whales swimming into water with heavy vessel traffic, it is “inevitable” that some are going to collide with vessels, she added. Probable or suspected vessel strikes have been confirmed to be the cause of death for three of the whales stranded this year, CalAcademy said.

“As of now, this is just being looked at as a blip,” Pemberton said. “It’s being considered to be just an anomalous bump, as opposed to an overarching issue with the species in general.”

The Cetacean Conservation Biology Team at the Marine Mammal Center has identified 33 individual gray whales swimming in the bay in 2025, marking an unusually high number, CalAcademy said. In 2024, there were just four distinct gray whales spotted in the bay.

Of the whales tracked, about one-third have remained in the bay for 20 days or more, CalAcademy said. The body condition of the whales ranged from emaciated to normal.

Scientists are studying why the whales have started entering the bay in larger numbers. The phenomenon is unusual, and the whales are remaining in the bay for longer periods than they used to, Pemberton said. While scientists are not yet sure why the whales are changing their habits, it could potentially be a result of adapting to changing ocean conditions, she added.

“It appears that some of them have determined that San Francisco Bay is a snack shack,” Pemberton said. “Unfortunately, that’s like building a snack shack in the middle of a four-way intersection.”

The whales migrate between Mexico and the Arctic, and it was previously believed that they did not stop to feed during their migrations, Pemberton said. That could potentially be changing because whales are undernourished from changing ice flows in the Arctic.

In about two weeks, the whales will begin their migration northward to reach the Arctic feeding grounds for the summer.

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CalAcademy has asked that boaters in the San Francisco Bay be “whale aware,” which includes slowing down and keeping an eye out for gray whales that have a lower profile in the water than other whale species. These guidelines apply to commercial ships and sailboats.

Pemberton added that this is a unique opportunity for people to see whales swimming in the bay.

“We don’t know if this is going to happen again next year, if this is a shift in the cultural behavior of gray whales or if this is just an anomaly,” Pemberton said. “I would take the opportunity to go out and see these whales, talk about them to your friends and keep the stewardship building so that these whales don’t fall off maps and people stop caring about the perils that they face out in the ocean.”