Dead gray whale washes ashore on Vallejo’s Mare Island

VALLEJO — A dead whale that washed up on the muddy shores of the Mare Island San Pablo Bay hiking trail earlier this week likely died from a vessel strike, according to an official with the Marine Mammal Center. 

Marine Mammal Center spokesperson Giancarlo Rulli said that the dead whale was first sighted May 12 at the Phillips 66 refinery in Rodeo. 

Refinery staff notified the California Academy of Sciences, which partners with the Marine Mammal Center, who sent experts the next day to inspect the whale.

The whale was stuck underneath a pier, which made access difficult, and only tissue samples and basic measurements were taken, Rulli said. The whale was determined to be a 39-foot adult female gray whale. 

Based on the observations made, Rulli said, “experts from the academy and the center suspect a possible vessel strike may have occurred prior to the animal’s death.”

On May 16, changing tides dislodged the whale and allowed it to later wash ashore on Mare Island. 

As of Thursday, the whale was in a state of decomposition and a putrid smell was present yards away. Closer inspection of the carcass reveals 6 large parallel slashes, consistent with a propeller strike. Blood can still be seen oozing from its wounds into the soft muddy waters. Its natural gray skin has turned into a purplish and yellowed sun baked tint.

While tissue samples might reveal more about the animals history, Rulli said that “due to the advanced state of decomposition and location, a necropsy will not be performed.”

This is the ninth whale to have died in the Bay Area this year, including eight gray whales and a minke whale.

Rulli said that the center’s Cetacean Conservation Biology Team “reported earlier this spring an unusually high number of sightings in the bay – 30 individual gray whales overall.” That’s almost eight times higher than last year’s, when only four were sighted.

“The reason or potential reasons behind the spike in sightings this year are still being investigated by researchers,” Rulli said.

In 2019, the National Oceanic and Atmospheric Administration announced an “unusual mortality event” for North Pacific gray whales along the West Coast of North America. 

Rulli called the event “in layman terms, an emergency decree for a species in crisis.”

The event lasted until 2023. During that four-year span, Rulli said that around 45% of the gray whale population died off. The main causes of death were from malnutrition, killer whale predation, entanglement, and vessel strikes

“Gray whales travel 10 to 12 thousand miles from Baja to the Arctic,” Rulli said. “The San Francisco Bay is a small puzzle piece in a massive migratory range. By collecting data here we can start sharing research with other experts in Mexico and Canada to understand the broader picture.” 

Why gray whales are entering the bay in such high numbers this year remains unknown.

“At this point it's a bit of a mystery,” Rulli said. “Not unprecedented, but the volume this year is even higher than during the mortality years, which took our experts by surprise.”

Considering the extra numbers of whales present in the Bay Area, Kathi George, director of the Cetacean Conservation Biology Team, said that “it’s important for all boaters to be extra vigilant and whale aware”.  

The U.S. Coast Guard started broadcasting messages to watch out for whales over marine frequencies and Bay Area ferries have modified their routes to avoid high whale density zones.

“It’s expected that most if not all gray whales will be out of the bay in the next couple weeks,” Rulli said, as the whales will continue their yearly migration northwards to their arctic feeding ground.

Considering the advanced state of decomposition, Rulli said that officials will not attempt to remove it and “it will likely remain there and further decompose.”

To report a dead, injured, or stranded marine mammal in the San Francisco Bay Area contact California Academy of Sciences at (415) 379-5381 for dead marine mammals or the Marine Mammal Center at (415) 289-SEAL for live ones.