Scientists say whale found off Alameda likely died from vessel strike

ALAMEDA, Calif. - A gray whale found floating off Alameda earlier this month likely died from blunt force trauma from a vessel strike, according to a necropsy report done 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, the two organizations said Tuesday in a joint statement.

During a necropsy Saturday, 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 couldn't 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," Moe Flannery, senior collections manager of ornithology and mammalogy at the academy, said in a statement. "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 whale was first reported to the academy on April 20 when it was spotted near the Robert W. Crown Memorial State Beach in Alameda. It landed the next morning slightly offshore on 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.  

Tides and extreme wind prevented scientists from performing the necropsy for several days, due to extreme wind conditions and the timing of tides. Collected materials -- including pelvic bones, stomach contents, and baleen -- will be used for research and collections.  

The number of gray whale strandings tends to increase between March and May when the whales migrate north toward Alaska. The whale's death occurred shortly after an unusual mortality event (UME) ended. 

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. National Oceanic and Atmospheric Administration officials estimated 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 strikes as the main causes of death.  

The academy and 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 postmortem 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." 

To report a dead, injured, or stranded marine mammal along the West Coast, call the West Coast region stranding hotline at (866) 767-6114. In the Bay Area, people should contact the California Academy of Sciences for dead animals at (415) 379-5381 or the Marine Mammal Center at (415) 289-SEAL (7325) for live animals.