A dead gray whale is pictured on Bolinas Beach in Marin County prior to a necropsy investigation by experts from The Marine Mammal Center and the California Academy of Sciences on March 25, 2023. The team of experts concluded the whale died as a result of blunt force trauma due to vessel strike.
Barbie Halaska © The Marine Mammal CenterA 35-foot-long North Pacific gray whale washed up on Bolinas Beach late last month – the first stranding of the year in the Bay Area – and local scientists say it likely died as a result of blunt-force trauma due to a vessel strike.
A team of 15 experts from the Marine Mammal Center and the California Academy of Sciences performed a necropsy of the male whale on March 25, two days after it became stranded on the beach just east of Duxbury Point. They determined the moderately decomposed animal had normal fat stores and blubber, indicating that it wasn’t malnourished. They also discovered bruising and hemorrhaging of the tissue on the left side of its head, extending from its left eye to the base of its skull, which is consistent with a vessel collision they suspect may have occurred while the whale was still alive.
“Gray whales are ocean sentinels due to their adaptability and foraging habits. They have a lot to tell us about the health of the ocean, so to see the species continue to face the added threats of human interaction should concern all of us,” Dr. Pádraig Duignan, director of pathology at the Marine Mammal Center, said in a statement.
The investigation into the deceased whale occurred just over a month after four gray whales were seen in San Francisco Bay for the first time this year. (The Marine Mammal Center told SFGATE the whale was not identified as one of those four whales or any others sighted in the bay in previous years.)
A gray whale is pictured exploring San Francisco Bay on February 23, 2023. Members of the Marine Mammal Center’s cetacean field research team have observed four whales in San
Francisco Bay this March.
The eastern North Pacific gray whale population is currently migrating north from their breeding grounds near Baja, Mexico to their feeding grounds in the Arctic. In recent years, sightings of the whales became more commonplace in San Francisco Bay and along the West Coast as they stopped over for extended periods to feed, possibly because changes in the Arctic environment made it more difficult for them to find food there. Increasing numbers of dead gray whales washing ashore in emaciated conditions caused the National Oceanic and Atmospheric Administration to declare an unusual mortality event in 2019.
The death of this particular whale is part of that ongoing event, which has caused the population to dwindle over time. The most recent estimate of the eastern North Pacific gray whale population recorded by the NOAA in the winter of 2021 and 2022 is approximately 16,650 whales — down 38% from a peak of 26,960 whales counted during the last assessment in 2015 and 2016. Malnutrition, entanglement and vessel strikes are all threats to the species, though researchers are also investigating the effects of other factors such as harmful algal blooms, infectious disease and natural predation.
Last month, Bill Keener, a field researcher with the Marine Mammal Center, told SFGATE the number of dead gray whales observed in the unusual mortality event since 2019 has been steadily decreasing. Data from the NOAA and the Marine Mammal Center shows a count of 34 gray whale strandings in California in 2019, 18 strandings in 2020, 19 strandings in 2021 and 10 strandings in 2022.
ALSO READ: Rare footage shows 30 orcas attacking whales in Monterey Bay
Of those gray whale strandings throughout the Bay Area in 2022, three of the animals likely died of ship strikes, one died of malnutrition, and three other deaths were undetermined.
"When a whale strands along the coast it allows us the unique opportunity to study the animal up close. It was a relief to see this young male gray whale in such good body condition with a thick layer of blubber and lots of fat and oil,” Moe Flannery, senior collections manager of ornithology and mammalogy at the California Academy of Sciences, said in a statement. “Although it is the first stranding of the year in the Bay Area, we are hopeful the good body condition is an indicator that the species is doing better now compared to the last few years."
The Marine Mammal Center said it’s “critical” for boaters and people on the water to keep a safe distance from whales and asks that ships reduce their speed limits to 10 knots (or 11 mph) in order to give whales more time to avoid a strike. People are also encouraged to report sightings of whales and other marine mammals on its website.
