Now, a group of scientists has calculated that humpback whales are eating millions of these microscopic pieces every day as they forage for food.
The study raises concerns about whales’ health, the study authors say, and is a sobering look at how widespread microplastic pollution has become in the world’s oceans.
“Large filter feeders like baleen whales evolved to process and filter vast amounts of the ocean,” Jeremy Goldbogen, one of the study authors and an ocean researcher at Stanford University, said in a press release.
“So they represent sentinels of environmental change including pollution like microplastics.”
The scientists put tracking devices on more than 200 humpback, fin and blue whales to track where the giant marine mammals were spending time catching fish and krill.
They combined that information with microplastic concentrations in the ocean to estimate just how much plastic the whales were eating. The results were published on Tuesday in the journal Nature Communications.
Blue whales — the largest animal on Earth — likely ingest up to 10 million individual pieces of microplastic every day, the study found.
The slightly smaller fin whales also eat between 3 and 10 million each day, and humpback whales can eat more than 1 million.
The microplastics were mostly in the whales’ food, not the water, the researchers noted. Blue, fin and humpback whales are all baleen whales, filtering water through the hair-like sieves in their mouths to catch tiny creatures called krill.
“The krill eat the plastic, and then the whale eats the krill,” study author Matthew Savoca, a post-doctoral biologist at Stanford, said in the press release.
Humpback whales who relied more on fish consumed fewer microplastics than those feeding more on krill, eating an estimated 200,000 pieces per day.
The study raises nutritional concerns for the whales, the authors add. The whales are spending time and energy to catch these krill, but all that non-nutritional microplastic could add up and deprive the animals of needed food.
“If patches are dense with prey but not nutritious, that is a waste of their time, because they’ve eaten something that is essentially garbage,” study author Shirel Kahane-Rapport, a post-doctoral ecologist at California State University, Fullerton, said in the press release.
“It’s like training for a marathon and eating only jelly beans.”
Earlier this year, nearly 200 countries agreed to create a treaty at the United Nations to address the global plastic pollution crisis.