Blue whales off the California coast eat up to 10 million microplastics per day

"The unique concern for whales is that they can consume so much," study co-author Matthew Savoca, a postdoctoral scholar at Hopkins Marine Station, Stanford’s marine laboratory on the Monterey Peninsula, said in a statement.

Whales are lower on the food chain, surprisingly

The whales mostly feed 50 to 20 meters below the surface of the ocean, a depth known to contain the highest concentrations of microplastic in the open water. While humpback whales consuming fish such as herring and anchovies ingest an estimated 200,000 pieces of microplastic per day, 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.

"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," said Savoca.

According to lead study author Shirel Kahane-Rapport, who worked on the research as a PhD student in the Goldbogen Lab at Stanford, the study shows that whales are not getting the right nutrition they require to survive.

"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," said Kahane-Rapport. "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."

Uncertainty over what happens with the microplastic after ingestion

Scientists will continue to investigate what happens with the microplastic ingested by whales. "It could be scratching the linings of their stomach. It could be absorbed into the bloodstream, or it could all pass through the animal. We don’t know yet," said Kahane-Rapport.

A range of technologies was used for the study, including drones and sensor-laden devices known as biologging tags, to collect movement and physiological data.

The published study is an imperative step towards understanding the "potential chemical and physiological effects of microplastics" on whales and other large filter-feeding animals, said senior study author Jeremy Goldbogen, an associate professor of oceans at the Stanford Doerr School of Sustainability. "Large filter feeders like baleen whales evolved to process and filter vast amounts of the ocean, so they represent sentinels of environmental change including pollution like microplastics."

Next, scientists will examine how forces in the ocean create "dense patches" of both microplastics and prey. And how microplastics affect the nutritional value of key prey species.

Study Abstract:

Microparticles, such as microplastics and microfibers, are ubiquitous in marine food webs. Filter-feeding megafauna may be at extreme risk of exposure to microplastics, but neither the amount nor pathway of microplastic ingestion are well understood. Here, we combine depth-integrated microplastic data from the California Current Ecosystem with high-resolution foraging measurements from 191 tag deployments on blue, fin, and humpback whales to quantify plastic ingestion rates and routes of exposure. We find that baleen whales predominantly feed at depths of 50–250 m, coinciding with the highest measured microplastic concentrations in the pelagic ecosystem. Nearly all (99%) microplastic ingestion is predicted to occur via trophic transfer. We predict that fish-feeding whales are less exposed to microplastic ingestion than krill-feeding whales. Per day, a krill-obligate blue whale may ingest 10 million pieces of microplastic, while a fish-feeding humpback whale likely ingests 200,000 pieces of microplastic. For species struggling to recover from historical whaling alongside other anthropogenic pressures, our findings suggest that the cumulative impacts of multiple stressors require further attention.