NOAA declared last week that the die-off was over.

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

Along the way, they dodge ships and fishing equipment, navigate polluted waters, and hide from hungry orcas. They also have to contend with biotoxins and infectious diseases.

So when researchers began looking at the whales bodies, they tried to determine which of these various calamities was the primary cause of the population die-off.

Although other gray whale die-offs have occurred along the Pacific Coast, they have been less closely researched.

In 1999 and 2000, 651 whales stranded onshore, but only three whales were necropsied. Another die-off in the late 1980s was studied even less.

This time, however, the scientific investigative team was large — spread across three nations — highly coordinated, and had access to new technologies, such as drones, which enabled them to create a more thorough picture of the whales who died, and those that remained alive.

“I think funding was a big part of it as well,” said Stephen Raverty, a veterinary pathologist with the Marine Mammal Research Unit in British Columbia, and lead author of the study. “It’s really afforded an opportunity to respond to these animals. And then we’re always trying to get the information back to the First Nations community or sharing it with the public. And I think that engages 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 with the national fisheries service’s Office of Protected Resources in Silver Spring, Md. He said Fauquier was instrumental in organizing the sharing of information across nations, departments and individuals.

But even with such resources, studying whale die-offs is difficult.

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