Four dead gray whales found dead in the San Francisco Bay Area in 9 days, raising concerns among biologists about the duration and severity of the giant mammals’ die-off, which is now in its third year.
“It’s alarming to respond to four dead gray whales in just over a week because it really puts into perspective the current challenges faced by this species,” says Dr. Pádraig Duignan, pathology director at The Marine Mammal Center.
On March 31, the first whale carcass appeared at Crissy Field in San Francisco. On Saturday, another was discovered in the Fitzgerald Marine Reserve at Moss Beach. A third was found floating in the bay on Wednesday and towed to Angel Island, where workers from the Marine Mammal Center in Sausalito were going to make a necropsy on Thursday morning when they received word that a fourth had washed up on Muir Beach.
The Marine Mammal Center announced on Friday that the 41-foot adult female discovered on Muir Beach died because of a ship strike. Biologists found signs of blunt-force damage, such as hemorrhaging and bruising across the animal’s jaw and neck—typical of an accident.
“Our team hasn’t responded to this number of dead gray whales in such a brief span since 2019, when we performed a startling 13 necropsies in the San Francisco Bay Area,” said Dr. Pádraig in a statement. “Gray whales are ocean sentinels because of their adaptability and foraging habits, meaning they have a lot to tell us about the health of the ocean, so to see the species continue to suffer with the added threats of human interaction is a major cause for concern.”
The necropsy of the gray whale towed to Angel Island revealed it was a young 37-foot male with no evidence of a ship hit or starvation, the two major causes of gray whale deaths in the last few years. According to the Marine Mammal Center, the same was true for the animal that washed up on Crissy Field.
The latest die-off connects with a recent pattern where gray whales have been spending a remarkably long time in San Francisco Bay while migrating from breeding grounds in Mexico to feeding grounds in Alaska.
“Normally, in a regular year you’d see one or two gray whales that would poke into the bay for a little, and then they would leave in a matter of hours,” said Bill Keener, research associate at the Marine Mammal Center. “That all changed in 2019, when we saw multiple gray whales – 10 to 15 – coming in and using San Francisco Bay as a migratory stop or rest stop.” Some stayed for an entire month.
When whales spend time in the bay, they are more likely to be struck by a ship because the bay is relatively small, and ships have brief space to maneuver. Furthermore, all of the whales that have passed through the region since 2019 have been extremely underweight, according to Keener. Gray whales are bottom feeders, scooping up sediment as they roll over the ocean bottom and picking out crabs and other edibles with their baleen plates.
There are two reasons for the extreme underweight that gray whales have in the last few years. The first one is that climate change is causing some of the sediment to move around, and it’s getting harder for whales to find the amount of food they require. The second reason holds that as the whale population grows, there is not enough food to go around in their feeding grounds. In general, Pacific gray whales are a success story, having recovered from near extinction because of the period of extensive whaling.
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The whales usually leave the Bay Area by May, and Keener isn’t sure whether the last four deaths are a fluke or part of a rising problem.
“How many will show up dead along those shores we just don’t know,” Keener said, “but it definitely causes concern when they’re in the bay.”