Famine has decimated the Pacific Coast gray whale population

When large numbers of gray whales began washing up along North America's Pacific coast nearly six years ago, marine scientists could only speculate about the cause: Was it a disease? Ocean pollution? Increased ship collisions?

Many of the stricken cetaceans appeared thin or emaciated, while others appeared torn apart by the killer whales. Some of them apparently died after being hit by a ship, or caught in fishing gear. And still others have not provided any clear evidence.

Now — after more than 700 gray whales have washed ashore in Mexico, Canada, California and other U.S. states since late 2018 — new research published Tuesday in PLOS One suggests the culprit has been a sharp decline in the availability of Arctic and subarctic food for mammals. Arctic seafloor feeding zones.

But what remains unclear is whether this malnutrition is caused by a change in the ocean, or by the whales themselves.

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“Did something happen to their food supply in those years that put them under severe nutritional stress and led to a lot of the whales being in very poor condition and dying?” Study co-author Padraig Duignan, a pathologist at the Marine Mammal Center in Sausalito, said:

“Or did the whale population grow to such a level that they competed with each other for food, and then a percentage of the population died off again because they couldn't compete for the available resources?” He said.

The research is based on an investigation launched by the National Oceanic and Atmospheric Administration in early 2019, after the whale deaths were declared an unusual mortality event, or UME. Researchers, monitors, and stranding coordinators across North America began working together, alerting each other about strandings; sending crews to document and collect tissue samples; and performing a necropsy (animal form of autopsy).

The National Oceanic and Atmospheric Administration (NOAA) investigation recorded 690 dead whales since January 1, 2019. However, researchers suspect the real number is thousands more. Most whales die at sea and sink to the bottom of the sea, out of sight or reach of humans.

Joshua Stewart, a quantitative ecologist at the Marine Mammal Institute at Oregon State University, who was not an author on this paper, estimates that gray whale numbers fell by half during the recent mortality event.

“The population has dropped to 14,000 people from 27,000 or so,” he said. “That's a big drop.”

A gray whale calf swims next to its mother in San Ignacio Lagoon, Baja California, in February 2021.

(Carolyn Cole / Los Angeles Times)

The National Oceanic and Atmospheric Administration (NOAA) announced last week that the die-off was over.

Every year, California gray whales make a roughly 13,000-mile round-trip from the cold waters of the Arctic to the temperate lagoons of Mexico's Baja Peninsula and back again. During the summer months, they feed on a variety of bottom-dwelling invertebrates, such as shrimp-like copepods, which thrive in the mud and sand of the Bering, Chukchi, and Beaufort seas. Here they mate, fill their bellies, and prepare themselves for the long journey south to the warm, sheltered nurseries of the shallow Baja estuaries.

Along the way, they dodge ships and fishing gear, navigate polluted waters, and hide from hungry killer whales. They also have to deal with biotoxins and infectious diseases.

So when researchers started examining whale bodies, they tried to determine which of these different disasters was the main cause of whale death.

Although other gray whale deaths have occurred along the Pacific coast, they have not been thoroughly researched.

In 1999 and 2000, 651 whales beached themselves, but only three whales were dissected. Another death in the late 1980s has been less studied.

But this time, the large scientific investigation team – spread across three countries – was highly coordinated, and had access to new technologies, such as drones, enabling them to build a more comprehensive picture of the whales that died, and those that survived. Alive.

“I think funding was a big part of it as well,” said Stephen Rafferty, a veterinary pathologist at British Columbia's Marine Mammal Research Unit and lead author of the study. “It's really given an opportunity to respond to these animals. And then we always try to bring information back to the First Nations community or share it with the public. And I think that attracts more people to actually want to contribute and participate in these efforts.”

He also gave a nod to co-author Deborah Fauquier, a veterinary medical officer at the National Fisheries Service's Office of Protected Resources in Silver Spring, Maryland. He said that Fokir was instrumental in organizing the exchange of information across countries, departments and individuals.

But even with these resources, studying whale deaths is difficult.

Despite hundreds of whales that washed ashore, researchers were unable to properly examine 61 of them.

This is because the majority of reported carcasses were discovered either weeks or months after the animal's death – and were too decomposed to be properly analyzed – or were located on remote islands, inaccessible bays, or on the bows of ships at sea.

After flying by helicopter, officials documented the carcass of a gray whale that washed up on Kodiak Island, Alaska, in September 2021.

(Carolyn Cole / Los Angeles Times)

Of the 61 whales they examined, the researchers determined the cause of death in just over half. Sixteen of them were severely emaciated and had probably died of starvation; 11 whales died from blunt force trauma – although two of those whales were also severely underweight; At least three were fatally injured by killer whales and two were entangled in fishing gear.

Overall, 18 whales were considered emaciated, 27 were considered “thin,” nine were considered average and two were considered obese. In the other five cases, nutritional status could not be determined.

One thing was clear: the death was not due to illness.

Deaths of large animals are often due to biotoxins, viruses, or bacterial infections. An example of this is the bird flu currently spreading around the world. Other examples include the domoic acid outbreak during the summer of 2023, which killed hundreds of sea lions and dolphins.

“We found no evidence of anything resembling an infectious disease,” Duignan said. “There were no obvious signs of infection of any kind. We ran a lot of tests for viruses, bacteria and toxins, and there was nothing significant.”

The question now is whether gray whale numbers will recover, continue to decline, or reach a sustainable level, given the dramatic changes occurring in their summer feeding grounds.

During this latest investigation, reports of unusual whale feeding behavior were observed relatively frequently, Rafferty noted. While the biological mantra has always been that gray whales only feed on bottom-dwelling creatures in the northern seas during the summer months – and quickly for the rest of the year – there have been reports of gray whales filter feeding and skimming krill from the surface. In places like San Francisco Bay.

The ability of gray whales to adapt has been known for a long time, but the frequency with which these behaviors occur indicates an immediate adaptive reaction to food shortages, or perhaps behaviors that no one has ever noticed.

That's partly what's so exciting about this research, Rafferty said. It has enabled scientists to build a baseline against which they can now make comparisons.

“If we look another five or 15 years, if we get another iteration,” he said, “they will have this data to compare.”

As for the future and population recovery?

“The way I think about it is these whales are not going away. They are not going extinct,” Stewart said. “But if the environment becomes much more marginal, we may not see as many whales as we did in the past when we had a polar region.” A really strong and productive north.” [seafloor] environments.”