You are what you eat—and for orcas, that’s bad news

Published: 11 October 2023

Researchers have known for decades that orcas across the North Pacific have harmful pollutants in their system.

Now, a new study reveals orcas in the western North Atlantic, including those in the Arctic, are significantly more contaminated than animals in the east—a finding that “shocked” study leader Anaïs Remili, a postdoctoral researcher at McGill, working with Associate Professor Melissa McKinney in the university's Department of Natural Resource Sciences. The research strongly points to their diet playing a major role in the level of pollutants, rather than their location.

The study looked at the presence of persistent organic pollutants, or toxic chemicals that degrade slowly and accumulate in the body, in the blubber of orcas across the North Atlantic. These pollutants, relics of industrial and agricultural processes, “have a nasty tendency to bind to fat,” says Remili, whose study was published in October in the journal Environmental Science & Technology. These chemicals weaken orcas’ immune systems, disrupt their endocrine function, impede growth and brain development, and even interfere with reproduction.

Contaminants amplify as they move up through the food chain, and the orcas that consume top predators—for example, those that primarily eat other marine mammals rather than fish—are most polluted. Thanks to their high body fat and position as apex predators, orcas are some of “the most contaminated animals on the planet,” Remili says.

As climate change worsens, so might orca pollution. For instance, warmer Arctic waters may draw more orcas north, where they’ll feed on high-fat marine mammals, Remili speculates.

“It tells us that we need to start acting now,” Remili says. She calls on countries to destroy toxic waste sitting in warehouses around the world and prevent new contaminants from being released.

“Killer whales are majestic animals,” she says. “If we don't have killer whales anymore, our ecosystems are going to be completely out of balance.”

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