SAN FRANCISCO – A gray whale found floating off the coast of Alameda on April 20 likely died due to blunt force trauma from a vessel strike, according to a necropsy.
The death marked the first “local cetacean mortality” of the year, the California Academy of Sciences said in a news release Tuesday.
Scientists with the academy and The Marine Mammal Center did the necropsy on Saturday. The whale was identified as a 40-foot adult female, with “full stomach contents and injuries consistent with blunt force trauma,” according to the academy.
The academy said the official cause of death could not be fully confirmed due to the decomposed state and body position of the whale.
The whale was first spotted near Robert W. Crown Memorial State Beach in Alameda on April 20. The next morning, it landed slightly off shore in a sandbar or mud deposit, before it dislodged and free floated with the tide, according to the academy.
On April 22, the whale was towed to a secure location on Angel Island.
The academy said extreme wind conditions and the timing of the tides delayed the necropsy for several days.
The number of gray whale strandings tends to rise between March and May, when the cetaceans pass by the Bay Area on their way to Alaska, according to the academy.
The academy said the whale’s death happened shortly after the National Oceanic and Atmospheric Administration, or NOAA, ended an unusual mortality event, or UME, involving North Pacific gray whales along the west coast of North America.
The UME was first declared in 2019, after changes in the whale’s feeding areas resulted in a die-off, according to the academy.
The academy said NOAA estimates the gray whale population declined from 20,500 whales in 2019 to 14,526 whales in 2023. Malnutrition, killer whale predation, entanglement and vessel strike were listed as the leading causes of death.
“We continue to document vessel strike injuries in gray whales in San Francisco Bay regardless of other threats to the animals,” said Denise Greig, an academy research scientist. “We hope the information we collect can contribute to making the Bay safer for whales, vessels, and people.”