Vessel Strike is Likely Cause of Death for Gray Whale Near Alameda

SAN FRANCISCO, CA (April 30, 2024) — A gray whale found floating off the coast of Alameda on April 20th likely died due to blunt force trauma from a vessel strike, according to a recent necropsy report conducted by scientists at the California Academy of Sciences and The Marine Mammal Center. The animal’s death marks this year’s first local cetacean mortality.

In a necropsy, or animal autopsy, conducted on Saturday, April 27, scientists identified the whale as a 40-foot adult female, with full stomach contents and injuries consistent with blunt force trauma. The official cause of death could not be fully confirmed due to the whale’s decomposed state and body position.

“Each whale that washes up is an opportunity for scientists to learn more about the species and the population,” said Moe Flannery, senior collections manager of ornithology and mammalogy at the Academy. “Although the Unusual Mortality Event (UME) investigation is now closed, the science does not stop. We will continue to gain as much knowledge as possible from each whale that washes ashore in our area.”

The gray whale was first reported to the California Academy of Sciences on April 20, 2024, when it was spotted near the Robert W. Crown Memorial State Beach in Alameda. The next morning, it landed slightly off shore in a sandbar or mud deposit, before it dislodged and free floated with the tide. On April 22, a towing team transported the whale to a secure location on Angel Island.

Scientists were unable to perform a necropsy on the whale for several days, due to extreme wind conditions and the timing of tides. Academy scientists were able to sample the skin and blubber while it was still floating near Alameda on April 21. Further materials—including pelvic bones, stomach contents, and baleen—were collected during the necropsy and will be used for research and collections.

The number of gray whale strandings tends to increase between March and May, when these cetaceans travel past the San Francisco Bay Area while migrating north toward Alaska. This gray whale’s death occurred shortly after NOAA ended the UME involving stranded North Pacific gray whales along the West Coast of North America.

The UME was first declared in 2019, after ecosystem changes in the whale’s Arctic feeding areas resulted in the die-off of hundreds of gray whales along the Pacific coast. NOAA estimates the North Pacific gray whale population declined from 20,500 whales in 2019 to 14,526 whales in 2023, listing malnutrition, killer whale predation, entanglement, and vessel strike as the main causes of death.

The Academy and The Marine Mammal Center are closely monitoring the deaths of cetaceans and pinnipeds in the Bay Area. In a recent publication co-authored by researchers from both organizations, scientists along the entire migratory path of the whales described post mortem findings from a subset of the UME whales.

“We continue to document vessel strike injuries in gray whales in San Francisco Bay regardless of other threats to the animals,” said Denise Greig, research scientist at the Academy. “We hope the information we collect can contribute to making the Bay safer for whales, vessels, and people.”

Local response to the dead whale was handled by representatives from the California Academy of Sciences, The Marine Mammal Center, and the National Oceanic and Atmospheric Administration (NOAA). The US Army Corps of Engineers, the US Coast Guard, and TowBoatUS coordinated the whale’s delivery to the necropsy location.

The Academy and the Center are grateful to its partners at Angel Island State Park, one of the many parks within the California State Park system, for their assistance in authorizing a landing area to perform the whale necropsies.

The response to this whale was funded by NOAA John H. Prescott Marine Mammal Rescue Assistance Grant #NA23NMF4390335 awarded to the California Academy of Sciences.

All marine mammal stranding activities were conducted under authorization by the National Marine Fisheries Service through a Stranding Agreement issued to the California Academy of Sciences (SA-WCR-2023-016) and MMPA/ESA Permit No. 24359.

To report a dead, injured, or stranded marine mammal along the West Coast (i.e., off California, Oregon, and Washington): West Coast Region Stranding Hotline: 1-866-767-6114. In the San Francisco Bay Area, please contact one of two hotlines:

• For dead marine mammals contact California Academy of Sciences: (415) 379 - 5381
• For live marine mammals contact The Marine Mammal Center: (415) 289 - SEAL (7325)

Video and photo assets of the whale can be found here.