Gray whales are dying in large numbers, again.

At least 70 whales have perished since the start of the year in the shallow, protected lagoons of Mexico’s Baja California peninsula where the animals have congregated for eons to calf, nurse and breed, said Steven Swartz, a marine scientist who has studied gray whales since 1977. And only five mother-calf pairs were identified in Laguna San Ignacio, where most of the wintering whales tend to congregate, Swartz said.

That’s the lowest number of mother-calf pairs ever observed in the lagoon, according to annual reports from Gray Whale Research in Mexico, an international team of researchers — co-founded by Swartz — that has been observing gray whales in Laguna San Ignacio since the late 1970s.

The whales are now headed north. In just the last two weeks, three gray whales have died in San Francisco Bay, one of which was described by veterinarians and pathologists at the Marine Mammal Center in Sausalito as skinny and malnutritioned. Evaluations on the two other deaths are still being conducted.

Alisa Schulman-Janiger, who has led the Los Angeles chapter of the American Cetacean Society’s gray whale census at Rancho Palos Verdes since 1979, said the number of whales she and her volunteers have observed migrating north this spring and swimming south this past winter is the lowest on record.

“We didn’t see a single southbound calf, which has never happened in 40 years,” she said.

Schulman-Janiger and other researchers aren’t sure why the whales are dying, although she and others believe it could be from lack of food based on the depleted conditions in which some of the whales have been found.

Eastern North Pacific gray whales cruise the Pacific coastline every year as they migrate 6,000 miles north from the Baja peninsula to their summer feeding grounds in Arctic and sub-Arctic regions. There, the leviathans gorge themselves on small crustaceans and amphipods that live in the muddy sediment of the Bering, Chukchi and Beaufort seas, before they head back south to loll, cavort and mingle in balmy Mexican waters.

The animals migrate through a gantlet of perils as they navigate some of the world’s most heavily shipped regions, maneuver through discarded fishing lines and gear, dodge pods of killer whales waiting to tear apart defenseless calves, and swim through waters polluted with microplastics, toxic chemicals and poisonous algae.

Most of the time, the bulk of them make the journey just fine.

But in 2019, large numbers of the whales began to die.

Starting that spring, biologists at the Laguna San Ignacio research station recorded roughly 80 dead whales in Mexican waters, and just 41 mother-calf pairs in the lagoon. They also noticed — using photographs and drone imagery — that roughly a quarter of the animals were “skinny.”

“You can see it in photographs,” said Schulman-Janiger, who described skinny whales as looking like they had necks because a thick fat pad that typically covers the area behind the skull is gone. “And you can see their scapulae,” she said, referring to the animals’ shoulder blades.

“You shouldn’t see a whale’s shoulder blades,” she said.

Then, as the hungry whales migrated north in 2019, large numbers began stranding on the beaches of California, Oregon, Washington and Alaska. By the end of that year, researchers had documented 216 dead whales on the beaches and near shore waters of the North American Pacific coastline.

A federal investigation by the National Oceanic and Atmospheric Administration into what is known as an unexplained mortality event was launched in 2019. The investigation allowed for scientists across multiple disciplines and institutions to gather and share knowledge to determine the cause of the die-off.

The cause of the deaths was never definitively established, and the investigation was closed in 2023 as the number of strandings fell into a range considered normal. Many researchers concluded a change in Arctic and sub-Arctic food availability (via massive changes in climate) was the driving factor. Their assessment was supported by the observations of malnutrition and skinniness in the whales and similar events and observations in other Arctic animals, including birds, seals, crabs and fish.

They also noticed that many of the whales had started feeding in areas — such as San Francisco Bay and the Los Angeles and Long Beach harbors — where such behaviors had never before been seen.

In the last two weeks, several gray whales have been observed in San Francisco Bay, including a near record high of nine on a single day. Reports of feeding behaviors had also been made, including off the city of Pacifica.

Asked whether the researchers at NOAA are noting these concerning observations and anticipating the possibility of another die-off, Michael Milstein, an agency spokesman, said the number of strandings along the Pacific coast is still low — just seven in California and one in Washington. The annual average is about 35.

He said it was too early in the whales’ northward journey to know for sure.

John Calambokidis, senior research biologist and co-founder of the Cascadia Research Collective, a marine mammal research center based in Olympia, Wash., agreed with Milstein: “We are just entering our main period of strandings (April to June) so a little early to draw any conclusions.”

And despite Schulman-Janiger’s concerns, she too said it is early — and that La Niña ocean conditions may be partly to blame for the low number of animals observed thus far.

She said reports from Mexico indicate many gray whales migrated farther south than they typically do, and have been seen swimming around the Gulf of California — off the coasts of Loreto, Cabo San Lucas and Puerto Vallarta.

She said that is good news if the low counts are due to the whales just being late. But worrisome if already food-stressed whales are having to tack on an additional 800 miles to their journey.

“It’s a very weird year for gray whales, and a concerning year given their body condition, the strandings and the very low calf estimates,” she said.