Why are so many gray whales dying in the Pacific?

PUERTO ADOLFO LÓPEZ MATEOS, MÉXICOAs early morning fog lifts off the Baja California coastline, Alushe Camacho steers a small fishing boat through a mangrove-lined estuary, his eyes fixed on the horizon. During most of the year, Camacho hunts grouper, sole, and hammerhead sharks. Today he’s in search of gray whales.

After several minutes Camacho spies his target: a heart-shaped cloud of ocean spray erupting from the water. Suddenly an adult whale thrusts its tapered head straight through the surface, pausing for five long seconds before disappearing under the waves.

Encounters like these have for decades drawn tourists to this marshy stretch of Mexico, where each winter thousands of Eastern Pacific gray whales arrive from Alaska’s Arctic. Here the adults mate, and females give birth and rear their young in a network of tranquil lagoons.

Over the dozen years he’s been guiding, Camacho, 33, has devised nicknames for whales that return each season. Lucrecio splashes boats with his tail; Olivia nudges her calves to be caressed by starry-eyed tourists.

But over the last three years, Camacho and others have noticed ominous changes. The whales are arriving in the estuary later in the year, and many appear malnourished, the jagged outline of vertebrae visible on their typically fatty backs. More whales than usual have been washing up dead along the shore.

Perhaps most concerning is the dramatic drop in births. On a normal early February morning like this one, Camacho would expect to see several pairs of mothers and calves. Today he spies only adults.

The changes observed in Mexico are evidence of a more widespread phenomenon, one brought to public attention in 2019 and 2020, when strandings of gray whales along the Pacific coast of North America surged dramatically. The National Oceanic and Atmospheric Administration (NOAA) declared an “unusual mortality event” and launched an investigation into the causes.

Between 2016 and 2020, the estimated population of eastern North Pacific gray whales plummeted by nearly a quarter, from almost 27,000 individuals to around 20,500. The origins of the decline are so far a mystery. Much of the early research points to climate change, which is rapidly warming the Arctic Ocean and may be reducing the quantity or quality of whales’ food supply. But scientists can’t rule out other factors, including the possibility that the whale population grew too large and is simply correcting itself.

Experts up and down the coast are urgently investigating because these mammals, with their 12,000-mile migrations, are critical barometers of ocean health. Gray whales are known for being a robust, adaptable species. Trouble for them could indicate much bigger problems—including along their feeding grounds on the sea floor, a crucial part of the marine food web and an area that scientists know relatively little about because it's so logistically difficult to study.

“They’re sentinels for what’s going on in the North Pacific ecosystem writ large,” says Sue Moore, a research scientist at the University of Washington who is helping lead NOAA’s probe.

The question has taken on a special urgency in Mexico, where a string of villages on the Baja peninsula have come to rely economically on the annual arrival of the whales.

“Something is happening, and we don’t know what it is,” says Camacho. “If the whales don’t return, what will we do?”

An intimate connection

Camacho has spent his entire life in Puerto Adolfo López Mateos, a dusty town of 2,000 five hours north of Cabo San Lucas. Living alongside a shallow lagoon that is home to dolphins, egrets, and pelicans, residents are closely connected to nature. Ospreys nest atop telephone poles, and coyotes slink down dirt streets, waiting for fishermen to dock with their daily catch.

But residents regard the whales with special reverence. A gray whale sculpture stands in front of the Catholic church, and whale murals adorn restaurants and the elementary school. Locals say that because they are born here, gray whales are Mexican. Each winter, the village celebrates their homecoming with a three-day festival, including concerts and a beauty pageant.

It wasn’t always this way.

In the 1800s and early 1900s, foreign whalers crowded these lagoons in search of blubber for producing lamp oil. Whalers had already, in the 1700s, hunted to extinction a separate stock of gray whales in the Atlantic Ocean. But with the rise of petroleum as lamp fuel, the establishment of the International Whaling Commission in the 1940s, and passage of the Marine Mammal Protection Act in 1972, the eastern North Pacific gray was able to bounce back.

By the 1970s, foreigners were again descending on the Baja coast not to hunt whales but to admire them. Eventually the Mexican government, setting a standard for sustainable eco-tourism worldwide, stipulated that tours must be conducted by local guides, which brought new job opportunities to a region formerly dependent on commercial fishing. The whales responded with unusual friendliness, often seeking out boats on their own and prodding tourists to stroke their heads or massage their baleen.

While working as a fisherman April through December, Camacho brings in on average $170 a week. When the whales arrive, he can earn six times as much guiding for Pirata Tours, the company founded by his grandfather four decades ago.

Over a dinner of red snapper that his brother, who is also a whale guide, had caught the day before, Camacho gestures around the property he recently purchased, which is lined with rustling palm trees and features a new building he hopes to turn into a fish-fileting business. “Everything is thanks to the whales,” he says.

Unraveling a coastal mystery

Omar García Castañeda is braced on the bow of a bumping motorboat, binoculars pressed to his face and a safety rope looped around his waist. It’s a blustery day to be out on the water, but time is precious: The gray whales inhabit their breeding grounds for about three months each year, and García and his colleagues must count and photograph as many of them as possible.

The marine biologists are part of the Laguna San Ignacio Ecosystem Science Program, a binational research group that has been monitoring whales along the Baja coast since 2007. Each year the group compiles photo catalogues of whales that allow them to track the movements of individuals, identified by their distinctive patterns of barnacles and scars. Crucially, in recent years the photographs have also been used to evaluate whale health.

The cetaceans are so huge—a healthy gray is 90,000 pounds and up to 50 feet long—that it can be difficult to determine from a boat deck whether they are malnourished. But photographs can reveal nuances: Do the whales have thick, rounded backs or a depression behind their heads? Are their scapulae protruding?

During the program’s first decade, the proportion of single adult whales deemed to be in poor body condition had remained steady, at around 6 percent. But that number began to rise in 2018. By 2020, it had hit 30 percent.

Drone photography confirmed the trend: between 2017 and 2020, a growing percentage of whales were much leaner than they should be.

All along their migration route, whales were stranding in record numbers. In 2019, 214 gray whales were found dead, including 122 in the United States—four times the nation’s annual average over the previous 18 years. Scientists believe that for each whale found on land, another five die at sea.

“We saw this coming, but there was nothing we could do about it,” says Steven Swartz, co-director of the Laguna San Ignacio program. 

Necropsies—post-mortem exams on animals—are particularly difficult to conduct on whales because they often wash up on remote beaches, and they decompose rapidly. In a typical year, researchers at the Marine Mammal Center, in Sausalito, might necropsy between one and three gray whales, which don’t typically enter San Francisco Bay while migrating. But in 2019, the center examined 13.

Pádraig Duignan, the center’s chief pathologist, speculates that whales veered off their usual route and entered the bay because they were hungry and looking for food. Necropsies revealed around half the whales were malnourished, with very low stores of fat around their hearts and other organs. Their entry into the bay made them particularly susceptible to boat traffic: Most of the other whales examined had succumbed to ship and ferry strikes.

In 2020, 174 gray whales washed up along the migration route. But Covid-19 restrictions limited researchers’ ability to perform necropsies. The Marine Mammal Center completed just one. 

Duignan didn’t know if whales were dying because of food shortages, disease, or possibly pollution, their bodies contaminated by the ingestion of microplastics. But it was clear, he said, that they were leaving the Arctic in a poor nutritional state. “They are not migrating with enough food ‘on board.’”

The starvation hypothesis has shifted investigators’ focus to Alaska’s Chukchi and Bering Seas, where whales binge during the summer and fall on bottom-dwelling shrimp-like amphipods, packing on stores of blubber for their eventual migration back south.

The Arctic seas, though, are changing. A warming climate means less sea ice, which disrupts the production of algae, which in turn feed amphipods. Could a shrinking ice cap be reducing the whales’ food supply?

That would be the simplest answer, but it is complicated by the fact that the gray whale population suffered another dramatic die-off in 1999 and 2000, a period when Arctic ice was far more abundant. Then, just like today, gray whales stranded up and down the coast, and scientists reported a 23 percent drop—from 21,000 whales in 1997 to 16,000 in 2000.

The whale population didn’t just recover after that event, it boomed, reaching 27,000 individuals in 2016.

Frances Gulland, who helped lead the NOAA team investigating the first die-off, doesn’t believe that climate change alone can explain two mass-casualty events two decades apart.

“Why was there 20 years between these die-off events when we know the changes in the Arctic have been continual?” the marine mammal veterinarian says. “It’s common sense that there must be problems with their feeding, and we also know that there are massive changes in the Arctic. But how those changes are connected is difficult to say.”

Others suggest that the gray whale population simply hit some sort of carrying capacity, then corrected itself—a process that may now be repeating.

Many believe it may be a combination of factors.

“I think we’re seeing an interaction of events,” says John Calambokidis, a biologist with the Cascadia Research Collective and with NOAA’s Unusual Mortality Event working group. An expanding population of whales would mean more competition for food. Paired with some other factor that may have triggered a decline in available prey—such as dramatic changes in the Arctic environment—starvation and death could follow.

In recent years, more gray whales have been veering a hundred miles off their migratory path and into Washington’s Puget Sound, where Calambokidis works, in search of food. It’s a sign that the whales are hungry, the researcher says, but it's also a sign of their resilience. Whales can pack on serious weight in just a few weeks—not by eating amphipods on the ocean floor but by feasting in ghost shrimp beds in shallow parts of the sound.

Calambokidis is hopeful that the gray whale population will recover, just as it did after commercial whaling and after the die-offs of 1999 and 2000. “Maybe gray whales are this adaptive because they’ve had to be,” he said.

A glimpse of the future?

The COVID-19 pandemic, which brought tourism in López Mateos to a near standstill, has given the community a sense of what life would be like without whales. Guides at the town’s impressive modern pier spend much of their time these days listening to cumbia music and cracking jokes as they wait for customers. This year’s Gray Whale Festival was canceled.

Fernando Rojas Rodriguez, 56, came here in 1990 in search of work. The whale business helped him put his four children through school. Now he worries—about the future of tourism during a global pandemic and about the health of the whales.

It is too early to say how strandings in 2021 will compare to the previous two years. Early reports from scientists working in Baja this season showed high rates of skinny whales and low numbers of mothers and calves. 

But on a recent morning, Rojas gets lucky. A woman and her daughter, tourists from Arizona, pull up in their rental car and ask to go out on the water.

As Rojas steers them slowly across the lagoon in his turquoise fishing boat, pods of dolphins arc in the distance, and pelicans cut through the moist air. And then he sees it: a cloud of mist erupting from a blowhole. Then another smaller spray shoots up next to the first.

Rojas cuts the engine. “It’s a mother and her calf,” he says excitedly. 

The baby, which he estimates is about a week old, is already the length of a large sedan. It darts toward the boat with a toddler-like curiosity, gliding along the bobbing vessel before diving down and emerging on the other side. Rojas tells the tourists to splash their hands in the water. The calf comes closer, and for a brief moment the daughter caresses its smooth, slate-gray skin.

A few minutes later, the mother and calf peel off. The baby has feeding to do, and the mother, crucial weeks of child-rearing. Within a month or so they’ll set out on their daunting journey north. Rojas hopes they will make it, and that later in the year they will find their way back.