Blue whales eat up to 10 million pieces of microplastic every single day, new Stanford University research has shown.
The largest animals ever known to have lived on Earth ingest up to 96 pounds (43.5 kg) of microplastic a day, the study suggested.
They found the whales predominantly feed 165 to 800 feet (50 to 244 metres) below the surface, a depth that coincides with the highest concentrations of microplastic in the open ocean.
Published in Nature Communications, the study focuses on blue, fin, and humpback whales.
The authors combined measures of microplastic concentrations up and down the water column off the coast of California with detailed logs of where hundreds of whales carrying tracking devices foraged for food between 2010 and 2019.
Study co-author Matthew Savoca, a postdoctoral scholar at Hopkins Marine Station, Stanford’s marine laboratory on the Monterey Peninsula said: “They’re lower on the food chain than you might expect by their massive size, which puts them closer to where the plastic is in the water.
“There’s only one link: The krill eat the plastic, and then the whale eats the krill.”
Humpback whales subsisting primarily on fish such as herring and anchovies ingest an estimated 200,000 pieces of microplastic per day, while those eating mostly krill ingest at least one million pieces.
Fin whales, which feed on both krill and fish, ingest an estimated three million to 10 million microplastic pieces per day.
Consumption rates are likely even higher for whales foraging in more polluted regions, such as the Mediterranean Sea, Savoca said.
The authors found nearly all the microplastics that whales consume come from their prey, not from the enormous volumes of seawater that these whales gulp when lunging to capture swarms of krill and small fish.
Lead study author Shirel Kahane-Rapport, said: “We need more research to understand whether krill that consume microplastics grow less oil rich, and whether fish may be less meaty, less fatty, all due to having eaten microplastics that gives them the idea that they’re full."
If true, this would mean each energetically expensive lunge by a whale may reap fewer calories – a price that an animal the size of an 18-wheeler can ill afford.
Kahane-Rapport said: “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. It’s like training for a marathon and eating only jelly beans.”
This is the first time the group’s rare trove of detailed information about whales’ lives and biology has been connected to plastic pollution, a rapidly proliferating problem that adds to threats from noise, chemical, and biological pollution.
Whales are hardly alone in their consumption of plastic, which was first reported in marine food webs 50 years ago and has now been found in at least 1,000 species.
“The unique concern for whales is that they can consume so much,” said Savoca.
Watch: Stanford study sounds the alarm over whales and microplastics