A juvenile minke whale tragically beached off the coast of Emeryville on April 8, after being spotted swimming around San Francisco Bay for nearly a week.
Initially, scientists believed the whale seemed healthy, but following an examination, they determined she was acting abnormally and ultimately decided to euthanize her due to illness.
This incident marked the fourth whale death in the San Francisco Bay within a short span of just a week and a half.
The previous three fatalities involved gray whales.
The first of these was a 36-foot-long female gray whale that washed ashore at Black Sands Beach in the Marin Headlands on March 30, with the cause of death still under investigation.
Two days later, on April 2, an adult male gray whale was found floating east of Angel Island, and the reasons for its death remain unknown.
Then, on April 4, a subadult male gray whale washed ashore at Fort Point Rock Beach near the Golden Gate Bridge in San Francisco.
Scientists confirmed that this whale likely died due to a vessel strike, according to reports from the Marine Mammal Center.
The increasing number of whale deaths raises alarms similar to previous years when “unusual mortality events” resulted in a heightened number of whale fatalities.
Kathi George, director of Cetacean Conservation Biology at the Marine Mammal Center in Sausalito, remarked, “This is unusual.
It takes me back to several years ago when we did have a large number of strandings happen at the same time.”
Despite the spate of whale strandings occurring in such a condensed timeframe, scientists emphasized that the overall number of whale deaths in the bay for the year remains consistent with historical levels.
Moe Flannery, the leader of the marine mammal necropsy team at the California Academy of Sciences, noted, “This is the normal time of year when gray whales are doing their northward migration from Mexico up to Alaska, so it’s not uncommon for us to have gray whales in and around San Francisco Bay in April and May each year.”
Flannery continued, “Although they seem high because they’re concentrated into a short period of time, the numbers of dead and stranded are not any different than the recent previous years.”
The causes of death for whales can vary significantly, including illnesses, malnutrition, and vessel strikes, as George explained.
“It’s coincidental that everything happened in a week and a half, but there are a lot of whales out there right now, and some of their physical condition that they’re in when they arrive in the bay may make them more susceptible to human impacts if they’re not as healthy,” she added.
Since 2016, scientists have observed whales entering San Francisco Bay during their annual migration between Mexico and the sub-Arctic.
George elaborated that the whales do not feed while in their breeding grounds in Mexico, and the energy they expend on mating, nursing, and giving birth leaves them fatigued for their long journey back north.
Consequently, scientists have noted that gray whales are attempting to feed in new locations, including San Francisco Bay.
This increased occurrence might also suggest that the whales are seeking resting spots before continuing their migration or adapting to climate changes, warmer ocean temperatures, or varying prey availability.
The Marine Mammal Center has documented at least 18 individual whales swimming in the bay this year, with almost daily sightings of gray whales reported since mid-March.
Reports indicate that most of these sightings have occurred east of Angel Island, stated Giancarlo Rulli, associate director of public relations for the Marine Mammal Center.
Between 2019 and 2023, gray whale populations faced a significant decline due to an unusual mortality event declared by the National Oceanic and Atmospheric Administration Fisheries.
During this period, over 40% of the gray whale population vanished within four years.
Rulli pointed out that during the unusual mortality event, 347 gray whale strandings were recorded across the United States.
“These whales basically left the Arctic with a half tank,” Rulli indicated.
He further explained that climate change has caused the highly nutritious food sources to shift further away, leaving whales to forage on less nutritious food while undertaking their extensive migration.
In the first four months of 2019, the onset of the unusual mortality event saw 34 dead gray whales wash up on California’s coastline, according to Flannery.
In contrast, only seven have stranded on the state’s shores so far this year.
Whether the recent spate of whale deaths indicates the beginning of another unusual mortality event remains under review, according to George.
She added that the data collected from the strandings will be instrumental in understanding the broader implications of these occurrences.
“We’re not there yet,” she concluded, emphasizing the importance of examining migratory patterns as a whole.
Scientists anticipate that whales will continue to be present in the bay through mid-May as they proceed with their northward migration.
Flannery also highlighted the importance of maritime awareness, stating, “Anyone using the water needs to be more aware of the animals that are sharing that environment.”
image source from：https://www.santacruzsentinel.com/2025/04/19/whales-strandings-san-francisco-bay/
