Why do dead whales keep washing up in San Francisco?

The 45ft carcass lay belly-up in the surf at Fort Funston beach, just south of San Francisco, drawing a small crowd of hikers and hang gliders. The stench lingered on the evening breeze as seabirds circled the animal, a juvenile fin whale. The whale was the fifth to wash ashore in the area this month. The other four were gray whales – giant cetaceans who migrate an astounding 11,000 miles each year from Alaska to Baja and back – all found on beaches near the city over a span of just eight days.

Each was a startling scene that raised immediate concerns for many observers. Whales are an important part of the ecosystem, often looked to as markers of ocean health, and their deaths can serve as indicators that something is amiss.

But scientists say the picture is more complicated. Investigations into the whale deaths continue and so far, experts say, there isn’t a smoking gun. Some marine researchers believe the deaths may be more cyclical than a sign of catastrophe.

“At first glance, it sounds horrific,” says Joshua Stewart, a research associate with the National Oceanic and Atmospheric Administration (Noaa). “But this is not an isolated event and to some extent that puts me at ease, personally.”

After nearing extinction in the 1950s, gray whales have had a remarkable recovery, rebounding to levels that enabled their removal from the endangered species list in 1994. Now they are among the most frequently sighted along the California coast as they migrate south for the winter and north in early spring.

They are also one of the most studied marine mammals, with data that goes back to the 1960s. Each time a whale winds up ashore, it gives scientists a new opportunity to learn about the state of seas.

However, the gray whale population on the west coast has declined in recent years – dropping by roughly 24% since 2016. Today there are an estimated 20,580 whales left, according to data from Noaa. And this month’s high spate of deaths was not the first – in 2019, Noaa declared an ongoing “unusual mortality event” when 122 whales washed up across the western shore from California to Alaska, more than four times the previous 18-year average of 29.

Stewart, who tracks gray whale population numbers, notes that, even with the declines, the population is still close to an all-time high. “Despite these downturns that, at the time, are very distressing, they have bounced back multiple times,” he says, adding that they are a highly adaptable and resilient species. “We want to know if this decline is continuing or a temporary thing.”

On 8 April, there were two whales to examine in the Bay at the same time. One carcass had been floating for days before it wound up lodged at the Berkeley marina. The other washed ashore on Muir Beach, just north of San Francisco. Teams from the Marine Mammal Center and the California Academy of Sciences conducted necropsies, which includes taking tissue samples, assessing the internal organs and reproductive tract, and evaluating the ribs and vertebrae for signs of trauma or impact.https://85b596cf40fb7e13ef1407c9db68d31c.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Moe Flannery, senior collections manager of birds and mammals for the California Academy of Sciences, was on the scene for the necropsies and says teams haven’t concluded their investigations – though culprits could include a lack of food or disease.

“There are no real answers yet,” she says, adding that despite the deaths, scientists are hopeful the gray whale population will bounce back. “They are a resilient species and I think it is concerning, but we have hope that this is just a little blip in time and that the species itself will rebound as it has in the past.”

Ship strikes have already been identified as the cause of some deaths, including the fin whale found on Friday. Unlike the gray whales, fin whales are still listed as endangered. There are only an estimated 3,200 left along the west coast off California, Oregon and Washington, and ship strikes are the biggest threat to their survival.

“It goes to show how many threats these whales are facing,” says Callie Steffen, a project scientist at the Benioff Ocean Initiative. Steffen works on a team that developed the Whale Safe project, which uses data to help mariners map where whales are when they plan voyages off southern California. The system, which she says is “like a Smokey the Bear fire warning but for whales”, has had a positive impact.

But whales may be traveling closer to the coast, putting them at higher risk of harm from ship strikes, loud disruptive noises from ports, chemical pollution and entanglement, according to a 2019 study from Scripps Institution of Oceanography at the University of California, San Diego. Authors of the study believe the change has something to do with the whales’ biological clocks.

Ari Friedlaender, a marine ecologist who teaches and heads a lab at the University of California at Santa Cruz, says that whether whales are killed by malnutrition or ship strikes, their deaths should be seen as red flags. Even if we can’t point our finger at a singular cause behind the decline, human activity – from shipping to the climate crisis – is driving changes that negatively affect the whales.

“It means people are likely affecting and altering the ecosystems that these whales require food from,” Friedlaender says. “There are so many downstream effects and impacts from the things we do in our daily lives. The actions we take locally can have consequences and impacts very far away and over longer periods of time. We need to keep our eyes open.”