Huge, decomposing whale carcasses are washing ashore throughout California’s Bay Area in unprecedented numbers. Ten dead gray whales have been reported at beaches from Rodeo in the East Bay to San Mateo just south of San Francisco since March.
Some were killed by ship strikes, and some from malnutrition, according to the Marine Mammal Center, a nonprofit organization and first-responder to these events. On Tuesday, the tenth dead whale was found near Linda Mar Beach in Pacifica, and is currently splayed across a rocky tidal area. Its age, sex, and cause of death are yet unknown.
To get a sense of how dire this is, take a look at the list of the nine previous deaths and their causes, circulated by the Marine Mammal Center in a statement:
March 10, 2019: San Francisco Bay; Cause of death: malnutrition
March 11, 2019: San Francisco Bay; Cause of death: malnutrition
April 02, 2019: Rodeo, CA; Cause of death: malnutrition
April 10, 2019: San Mateo, CA; Cause of death: ship strike
April 13, 2019: Richmond, CA; Cause of death: suspected ship strike
April 13, 2019: Hercules CA; Cause of death: malnutrition
April 16, 2019: Pacifica, CA; Cause of death: ship strike
April 30, 2019: Point Reyes National Seashore; Cause of death: pending investigation result
May 6, 2019: San Francisco, CA; Cause of death: ship strike
Due to the precariousness of the latest dead whale’s resting place, “it’s unsafe for the Center’s necropsy team to attempt to perform a necropsy, or animal autopsy,” said Marine Mammal Center spokesperson Giancarlo Rulli in an email. “The incoming storms and uncertain tidal conditions this week will play a role on when the expert team can investigate the carcass.”
Marine mammal experts say that an interconnected chain of events stemming from human activity is likely responsible for the whales’ deaths.
“These mother whales are worn out and running on empty, making them even more susceptible to negative human interactions, including ship strikes and entanglements,” Padraig Duignan, chief research pathologist at the Marine Mammal Center, said in a statement.
Blunt-force trauma from ship strikes is one of the most common causes of whale deaths in the Bay Area. A necropsy of one of the whales, a 41-foot-long adult female, revealed fractures to her skull and upper vertebrae, along with bruising and hemorrhaging consistent with a collision, the Marine Mammal Center said.
Biologists suspect that malnutrition is throwing a wrench in the whales’ journey to Arctic waters each spring.
Gray whales summer along the Alaska coast in the Chukchi Sea, skimming up tiny, mud-dwelling crustaceans called amphipods. When the summer ends, they head south toward Baja California Sur, Mexico and wait to repeat the migration process next spring.
“It is normal for gray whales to fast for about half the year,” said Regina Guazzo, a researcher at the Naval Information Warfare Center who studied gray whale migration at the Scripps Institution of Oceanography. “If gray whales are starving, it means that they didn't eat enough food the previous summer.”
Amphipods play a humble role in the greater food chain, feeding fish that in turn feed whales, seals, and other predators. But Arctic ecosystems are fragile, and the plankton are vulnerable to thinning sea ice as a result of climate change.
“If the ice melts too early, not enough phytoplankton food will sink to the sea floor and the amphipod populations could decrease,” Guazzo said. Over the past 30 years, scientists have seen amphipod populations—and, as a result, gray whale feeding grounds—move farther north, extending the distance of the whales’ migration route.
In a statement, the Marine Mammal Center also blamed overfishing for reducing prey availability.
Duignan said he hopes the whales’ deaths aren’t in vain. He would like to see this information used to better protect ocean areas, and adapt rules for shipping lanes that bisect whale migration routes.
“The good news is, even though we are seeing more strandings this year, the gray whale population along our coast is doing well,” Guazzo added. The National Oceanic and Atmospheric Association estimates that number is roughly 27,000 individuals.
“Fewer gray whale calves have been sighted this year, probably also related to low food in the Arctic,” said Guazzo, “but hopefully this summer the gray whales will have plenty of food to eat and the population will remain stable.”