Cause of Death Still Unknown for Gray Whale that Washed Ashore at San Francisco’s Ocean Beach

Experts were unable to confirm a cause of death for a gray whale that washed ashore in San Francisco this weekend. Scientists from The Marine Mammal Center, the world’s largest marine mammal hospital, as well as from the California Academy of Sciences investigated the animal’s death in a necropsy Monday afternoon. The team took a variety of samples for testing to hopefully shed light on this whale’s unique 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,” says Dr. Pádraig Duignan, Director of Pathology at The Marine Mammal Center. 

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.

During Monday’s necropsy, scientists identified the whale as a 45-foot adult female in average body condition based on the fat stores and blubber layer. The team noted the whale was in relatively fresh condition based on the quality of the skin, internal tissues, and organs. Scientists discovered multiple fractured spinal vertebrae but the lack of bruising and hemorrhaging to nearby tissue indicates the animal was most likely hit by a ship after it had already died of another cause. 

The team noted the whale had very minimal stomach contents and it was unclear why this adult female whale was migrating north to cool, food-rich Arctic waters so late this season. Gray whales do not have a calf every year and typically, when not accompanied by a calf, adult females migrate north early.

Elevated numbers of dead gray whales washing ashore in poor body condition since early 2019 across the species’ entire migratory range caused the National Oceanic and Atmospheric Administration (NOAA) to declare an Unusual Mortality Event (UME) that is ongoing. 

Malnutrition, entanglement and trauma from ship strikes are the most common causes of death in whales identified by the Center’s research team in recent years. The Center’s team participates as an investigator on NOAA’s gray whale UME working group, which assesses those factors as well as the impacts from harmful algal blooms, infectious disease, natural predation, and human interactions.

"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,” says Moe Flannery, Senior Collections Manager of Birds and Mammals for the California Academy of Sciences. “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."

Researchers from the Center observed increased numbers of gray whales in the San Francisco Bay this spring. The whales stayed for longer durations as a lay-over on their migration than in previous years and Center experts also documented them feeding in the Bay too. 

It is critical for boaters and people on the water to keep a safe distance from whales and report sightings to the Center’s hotline at 415-289-SEAL (7325). All marine mammals are federally protected, and the public should not approach any whale, alive or dead.

The Center’s researchers study the locations and behaviors of whales in San Francisco Bay so that informed decisions can be made to better protect whales. Public funding and support for this investigatory work is essential.

Scientists from The Marine Mammal Center and the California Academy of Sciences were able to collect a series of samples for ongoing research projects. Typically, the California Academy of Sciences archives various parts of each specimen (baleen, pelvic bones, blubber, muscle, etc.) in their scientific research collection thus making them available to scientists from around the world. 

The team received permission to perform the investigation on Ocean Beach, part of Golden Gate National Recreation Area, from the National Park Service. Logistics are being coordinated by the Park Service for the burial of the whale’s remains at the beach.

For more information or to set up an interview on this topic, please contact us at media@tmmc.org.

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