Here's Why Ocean Animals Keep Eating Plastic

Why do top ocean predators eat gloves? Or rope? Or plastic containers? How does a fish find itself with kilograms of garbage in its stomach?

There is a lot we still don't realize about what eating plastic and other refuse do to marine animals, or why they eat it, or how it makes them feel. While the necropsies reveal a shocking bounty of harmful material, ingesting plastic isn't generally a quick killer. More often, the toll comes during a slow creep, harming some species more than others, in ways both stealthy and subtle.

Even so, there are observable incidents that we can look at and pick bits and pieces of information that we can list as the things that we do know.

WHY DO MARINE ANIMALS EAT PLASTIC?

Scientists struggle with this question, says Matthew Savoca, a postdoctoral researcher at Hopkins Marine Station at Stanford University and a National Geographic Explorer. We all know that plastic is everywhere. Some 18 billion pounds of it flow into our oceans per annum. We all know that animals are having it. But we are finding the why behind what's really tough. Savoca told National Geographic what almost everyone are limited to what is happening in the ocean.

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

These species hunt deep within the ocean, sometimes quite 500 meters below the surface, where it's coal-black. They use echolocation to trace for food-typically squid. It's possible, says Savoca, that plastic trash seems like food to toothed whales.

WHY AREN'T OTHER WHALES HAVE PLASTIC-FILLED STOMACHS?

Baleen whales, like humpbacks and blue whales, have natural filters for his or her food. The brush-like baleen they need in their teeth and their narrow throats keep them from ingesting anything much larger than the krill-small crustaceans that swarm in large, mobile packs-that forms the idea of their diet. That helps explain why they're not ending up beached with stomachs filled with debris, but Savoca and his team are currently studying how and whether baleen could also be letting through smaller plastic particles. "Numerous questions remained unanswered," he says.

ARE WHALES EATING MORE PLASTIC THAN OTHER SPECIES?

Not necessarily. Flesh-footed shearwaters-large, sooty brown seabirds that nest on islands off the coasts of Australia and New Zealand-eat more plastic as a proportion of their body mass than the other marine creature.

But whale deaths are always noteworthy because we see so few of them. The overwhelming majority of whales die stumped, sinking to the ocean bottom faraway from the land. tons of animals, including shearwaters, albatross, and fish, don't get noticed once they ruin on a beach, says Savoca.

HOW DOES EATING PLASTIC HURT ANIMALS?

Sometimes, death by plastic is apparent-if, as an example, albatross chicks are found dead with only plastic and no food in their stomachs, or if a whale's necropsy shows intestines perforated by sharp plastic.

The harm is more stealthy most of the time which is likely manifesting as a chronic, unrelenting hunger or lethargy.

Whales need to surface to breathe, which suggests deep-dive foraging trips are time-sensitive. This deficiency, Savoca says, would make it tough for an animal to possess the energy to try to do everything it must do, like breeding, migrating, and continuing to forage.

And plastic comes on top of other stressors affecting life within the ocean-climate change, overfishing, shipping traffic, sound pollution. "It's a true shame because their lives are challenging enough even without the extra pressure we put onto them," says Savoca. Especially at speed, we're altering their environment, he says.