dead whales

Scientists Unable to Confirm Cause of Death for Whale That Washed Up in San Francisco

Adult female gray whale that washed ashore on Sunday, June 20, at Ocean Beach in San Francisco.
Katie D’Innocenzo © The Marine Mammal Center

Why a gray whale that washed ashore last weekend in San Francisco remains a mystery after experts performed a necropsy Monday.

The death marks the 14th since April and is the highest number of whale deaths in the region since an unusual mortality event was declared in 2019, according to The Marine Mammal Center, based in the Marin Headlands.

Scientists confirmed Tuesday that they were unable to confirm the cause of death following a necropsy Monday afternoon on Ocean Beach, but they took samples of the whale for testing and that may help experts understand the whale's story.

"Gray whales are sentinels for ocean health so performing these investigations is essential to better understand how human activity and changing environmental trends are impacting this species," said Dr. Padraig Duignan, director of pathology at The Marine Mammal Center, in a statement.

"While this whale's death remains a bit of a mystery, the high number of dead gray whales in the San Francisco Bay Area reinforces the need for us to continue to perform both observational research of live whales as well as necropsy investigations so that this critical data can be shared with key decision-makers," Duignan added.

That may prevent more deaths.

Scientists Monday were able to find out the whale was a 45-foot adult female whose body condition was average based on blubber layer and fat stores.

The whale had multiple fractured spinal vertebrae, but it was not bruised or hemorrhaging nearby so scientists believe it was hit by a ship after dying of another cause.

The scientific team discovered very little food in the whale's stomach. Also, the team noted the whale was heading north to food-rich Arctic waters late in the season.

Gray whales will migrate north early when they don't have a calf with them and this one didn't appear to have been nursing recently.

An unusual mortality event, declared by the National Oceanic and Atmospheric Administration, has been ongoing since 2019, because a larger than usual number of gray whales in poor body condition have been washing ashore along the species' entire migratory range, according to The Marine Mammal Center.

Scientists at the center have discovered that malnutrition, entanglement and ship strikes are the most common reasons whales have been found dead in the Bay Area in recent years.

Other reasons include harmful algal blooms, disease, predators, and human interaction.  

"Adult females with calves are usually the last to migrate north to the summer feeding grounds in Alaska. However, this adult female did not show signs that she had recently nursed a calf," said Moe Flannery, senior collections manager of birds and mammals for the California Academy of Sciences, in a statement. 

"We are hopeful that samples taken during the necropsy will shed some light on the reasons behind her late journey north and any potential ailments that may be affecting the gray whale population," Flannery said.

Arrangements are being made to bury the whale at Ocean Beach, which is part of the Golden Gate National Recreation Area.

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