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The Sausalito-based Marine Mammal Center is probing the death of a female gray whale that washed up on Black Sands Beach in the Marin Headlands.
The decomposing 36-foot whale carcass was the first found in San Francisco Bay this year, according to the center. Researchers have been closely monitoring whale activity since the beginning of March after an influx of sightings.
“What we are seeing currently unfold in San Francisco Bay is mostly expected,” said Kathi George, director of cetacean conservation biology at the center.
“Gray whales migrate past the bay during this season to their traditional feeding grounds in the Arctic,” George said. “However, we are seeing more gray whales enter the bay compared to last year. How gray whales use the bay and when they may come into the bay is being actively studied.”
George said last week there were seven confirmed sightings in one day. She warned that while it may be exciting to see, it raises concerns about human and whale safety.
“Gray whales are difficult to see due to their low profile and coloration patterns that naturally blend into the bay,” George said. “It’s important for all boaters to be extra vigilant and whale aware.”
The uptick in sightings suggests that whales are exploring more habitat, opportunistically feeding when possible, and that more people are observing and reporting them, George said.
The Black Sands whale was first discovered floating underneath the Golden Gate Bridge on Saturday. George’s team and researchers at the California Academy of Sciences responded to collect a skin and blubber sample, tag the animal and take pictures to identify it. It washed ashore the next day.
Researchers performed a necropsy at the beach on Monday. Initial results were inconclusive.
Researchers said the body is in an emaciated state. There are no signs of blunt force trauma, which would indicate a suspected ship strike — a common fatal threat for the creatures — while the whale was still alive.
Tests could take several weeks to process before a cause of death could be determined, researchers said.
Gray whales make one of the longest migrations of any whales in the world. After using the summer to feed and fatten up in Alaska, the whales migrate to Mexico in the winter to breed and give birth.
Over the past decade, the population numbers have fluxuated. A mass die-off between 2019 to 2023, which the National Oceanic and Atmospheric Administration labeled an “unusual mortality event,” was likely due to a food shortage in the Arctic caused by changes in sea ice, wind patterns and other factors.
The resulting four-year period saw a loss of more than 45% of the eastern North Pacific population, according to the Marine Mammal Center. Malnutrition, killer whale predation, entanglement and vessel strikes were documented as the main causes of death, researchers said.
In 2023, gray whale numbers began to rebound to as many as 21,000. NOAA declared an end to the “unusual mortality event” in November that year.
“It is very important that we as people give these whales plenty of space while they are migrating, foraging and caring for calves,” George said. “While on the water, you can help by reducing vessel speed, staying alert, and report sightings.”
George is encouraging anyone who spots a whale swimming in the bay or the Golden Gate to report it to the Marine Mammal Center via the Whale Alert app at bit.ly/4cnTgGa or by calling 415-289-7325.
People who spot dead marine mammals should report it the California Academy of Sciences at 415-379-5381.
