Why do ocean animals eat plastic?

Whales with stomachs full of plastic have turned up around the world. Here’s what we know.

Why would an apex ocean predator eat gloves? Or rope? Or plastic cups? How does a whale end up with more than 200 pounds of waste in its stomach?

Last week, a ten-year-old whale was found dead on a beach in Scotland. A necropsy revealed 100 kg of plastic and other rubbish congealed in clumps in his digestive system. The tragedy grabbed headlines—the sheer quantity of debris eclipsed that found in a growing number of similar cases: large whales discovered dead on beaches around the world with stomachs full of rubbish.

In November 2019, a young sperm whale was found dead on a beach on the Isle ...

In November 2019, a young sperm whale was found dead on a beach on the Isle of Harris, in Scotland. A necropsy found a 100kg tangle of litter in his stomach.

It’s unclear if these sightings are becoming more common, or if we’re simply more attuned to them now that the public is aware of the plastic crisis, but plastic production is increasing exponentially—In 1950, we produced 2.3 million tonnes of it. In 2015, we produced 448 million tonnes. Production is expected to double by 2050.

There is so much we still don’t know about what eating plastic and other refuse does to marine animals, or why they eat it, or how it makes them feel. While the necropsies reveal a shocking bounty of inedible material, ingesting plastic isn’t generally a fast killer. More often, the toll comes in a slow creep, harming some species more than others, in ways both stealthy and subtle. Here’s what we do know.

Why do marine animals eat plastic?

Scientists struggle with this answer, says Matthew Savoca, a postdoctoral researcher at Hopkins Marine Station at Stanford University and a National Geographic Explorer. We know that plastic is everywhere. Some 18 billion pounds of it flow into our oceans every year. We know that animals are eating it. But finding the why behind the what is really tough. “We know shockingly little about what’s actually happening in the ocean,” Savoca says.

Conventional wisdom suggests that animals eat plastic because it’s there and they don’t know any better (to some animals, like anchovies, plastic may smell like food). But that doesn’t explain why only certain types of whales—deep-diving toothed whales, such as sperm whales, pilot whales, and beaked whales—turn up dead on beaches with stomachs full of plastic.

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