Gray whales face mass mortality event along Pacific Coast

By Pooja Mamnoor

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    4/15/25 (LAPost.com) — Gray whales are experiencing another mass mortality event along the North American Pacific coastline, with at least 70 whales perishing since the beginning of the year in Mexico’s Baja California peninsula.

Scientists are recording alarming statistics – including the lowest number of mother-calf pairs ever observed in key breeding lagoons – raising concerns about a potential repeat of the 2019 die-off, which claimed hundreds of whales.

The declining population was first noticed in Mexico’s shallow, protected lagoons where the mammals traditionally congregate to calve, nurse, and breed. Steven Swartz, a marine scientist who has studied gray whales since 1977, reported only five mother-calf pairs were identified in Laguna San Ignacio this season, the lowest number ever recorded according to data from Gray Whale Research in Mexico.

As the whales continue their northward migration, the death toll is mounting. Three gray whales have died in San Francisco Bay within the past two weeks. One of these whales was described by veterinarians and pathologists at the Marine Mammal Center in Sausalito as emaciated and malnourished, while evaluations on the other two deaths are ongoing.

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, reported unprecedented low numbers in her observations. “We did not see a single southbound calf, which has never happened in 40 years,” she said.

Researchers have not definitively determined why the whales are dying. However, based on the depleted physical condition of some specimens, malnutrition is suspected as a primary factor. Many of the observed whales appear visibly underweight, with Schulman-Janiger describing them as looking like they have necks because the thick fat pad typically covering the area behind the skull is absent.

“You can see their scapulae,” Schulman-Janiger explained, referring to the animals’ shoulder blades. “You should not see a whale’s shoulder blades.”

Eastern North Pacific gray whales undertake an annual 6,000-mile migration between their winter grounds in Baja, California, and their summer feeding areas in the Arctic and sub-Arctic regions. In these northern waters, they consume small crustaceans and amphipods found in the muddy sediment of the Bering, Chukchi, and Beaufort seas before returning south.

This migration route exposes the mammals to numerous threats, including busy shipping lanes, abandoned fishing gear, killer whale predation, and waters contaminated with microplastics, toxic chemicals, and harmful algae. Despite these challenges, most whales typically complete the journey without incident.

A similar die-off event occurred in 2019, when researchers documented approximately 80 dead whales in Mexican waters and noted roughly 25% of the observed animals appeared malnourished based on photographic and drone evidence. That year, as the whales migrated north, strandings increased dramatically along the coasts of California, Oregon, Washington, and Alaska.

By the end of 2019, scientists had documented 216 dead whales on the beaches and nearshore waters of the North American Pacific coastline. This prompted the National Oceanic and Atmospheric Administration (NOAA) to investigate an “unexplained mortality event.”

Although the investigation closed in 2023 as mortality rates temporarily returned to normal ranges, researchers never established a definitive cause for the 2019 die-off. Many scientists concluded that changes in Arctic and sub-Arctic food availability, likely resulting from climate change, were the primary factors. This assessment was supported by observations of malnutrition in the whales and similar adverse effects noted in other Arctic wildlife, including birds, seals, crabs, and fish.

Scientists also observed unusual feeding behaviors, with whales foraging in locations such as San Francisco Bay and the L.A. and Long Beach harbors, where such activity had not previously been documented. Similar behaviors are being reported this year, with several gray whales recently observed feeding near San Francisco and Pacifica.

When asked about the possibility of another significant die-off, Michael Milstein, a NOAA spokesman, indicated it may be too early to draw conclusions. He noted the number of strandings along the Pacific coast remains relatively low so far this year, with just seven in California and one in Washington, compared to an annual average of approximately 35.

“We are just entering our main period of strandings (April to June) so a little early to draw any conclusions,” John Calambokidis, senior research biologist and co-founder of the Cascadia Research Collective in Olympia, Washington, said.

Despite her concerns, Schulman-Janiger also acknowledged current La Niña ocean conditions might partially explain the low whale counts observed thus far. Reports from Mexico indicate many gray whales have migrated farther south than usual this year, with sightings around the Gulf of California near Loreto, Cabo San Lucas, and Puerto Vallarta.

While this extended southern distribution could explain the lower counts if the whales are simply delayed in their northern migration, it raises additional concerns about already food-stressed animals having to travel an extra 800 miles. “It is a very weird year for gray whales, and a concerning year given their body condition, the strandings and the very low calf estimates,” Schulman-Janiger said.

A 25-foot long dead gray whale washed ashore on April 11 near the Huntington Beach Pier. The Pacific Marine Mammal Center started a necropsy to investigate the cause of death.

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