Whale consumes about 10 million pieces of microplastic per day
Scientists at Stanford University have found that the largest animals ever known to have lived on Earth eat a lot of tiny pieces of plastic.
The study, which was published in Nature Communications, looks at how blue, fin, and humpback whales eat tiny pieces of plastic, called microplastics, that are no bigger than a few grains of sand. The authors measured the amount of microplastics in the water column off the coast of California and kept detailed records of where hundreds of whales with tracking devices went to find food from 2010 to 2019.
They found that most whales eat between 50 and 250 meters below the surface, which is where the most tiny pieces of plastic are found in the open ocean. The blue whale, which is the largest animal on Earth, eats about 10 million pieces of plastic every day because it almost only eats krill, which are shrimp-like creatures.
“They’re lower on the food chain than you might think, given how big they are, 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 study co-author Matthew Savoca, a postdoctoral scholar at Stanford’s marine lab on the Monterey Peninsula, Hopkins Marine Station.
Humpback whales that eat mostly fish like herring and anchovies, eat about 200,000 pieces of microplastic every day. Those that eat mostly krill, eat at least 1 million pieces of microplastic every day. Fin whales eat both krill and fish, so they eat between 3 and 10 million pieces of microplastic every day. Savoca said that whales that eat in places with more pollution, like the Mediterranean Sea, are likely to eat even more.
The authors found that almost all of the tiny pieces of plastic that whales eat come from their food, not from the huge amounts of seawater that whales swallow when they dive for krill and small fish.
The lead study author, Shirel Kahane-Rapport, who worked on the research as a Ph.D. student in the Goldbogen Lab at Stanford, said that this is a worrying finding because it suggests whales may not be getting the food they need to stay healthy.
“We need more research to find out if krill that eat microplastics get less oily and if fish that have eaten microplastics that trick them into thinking they’re full are less meaty and less fatty,” said Kahane-Rapport. If this is true, it means that each whale lunge, which takes a lot of energy, may not give the whale as many calories as it could. This is a price that an animal the size of an 18-wheeler can’t pay.
Kahane-Rapport, who is now an NSF postdoctoral scholar at California State University, Fullerton, said, “If patches are dense with prey but not nutritious, that is a waste of their time, because they’ve eaten something that is basically garbage. It’s like training for a marathon and only eating jelly beans.”
The research builds on more than a decade of collecting and analyzing data, which has helped Goldbogen and his colleagues answer simple but important questions, like how much whales eat, how they eat, why they don’t grow bigger, and how slowly their hearts beat.
They use a variety of technologies, such as drones and biologging tags, which Goldbogen’s team sticks to the backs of whales to get information about their movements and health. They also put out echosounders from small research boats. These devices use sound waves to map the depth and density of fish and krill patches near where whales feed.
This is the first time that the group’s rare collection of detailed information about whales’ lives and biology has been linked to plastic pollution, a fast-growing problem that adds to the threats from noise, chemical, and biological pollution. “Our findings suggest that the cumulative effects of multiple stressors need more attention for species that are struggling to recover from past whaling and other human-made pressures,” the authors write.
Plastic was found in marine food webs for the first time 50 years ago and has now been found in at least 1,000 species. Whales aren’t the only ones who eat it, though. “Whales are a unique worry because they can eat so much,” said Savoca.
“Large filter feeders like baleen whales have evolved to process and filter huge amounts of ocean, so they are sentinels of environmental change, including pollution like microplastics,” said Jeremy Goldbogen, the lead author of the study and an associate professor of oceans at Stanford’s Doerr School of Sustainability.
Scientists are still looking into what happens when whales eat small pieces of plastic. “It could be scratching the linings of their stomachs. It could be absorbed into their bloodstream, or it could all pass through the animal. We don’t know yet,” said Kahane-Rapport, whose research at CSU Fullerton focuses on taking ideas from whales’ sieve-like baleen plates to make better systems for filtering out plastic pieces and other unwanted materials in industrial settings like wastewater treatment plants.
Goldbogen said that the new results are an important first step toward figuring out what chemical and physiological effects microplastics might have on whales and other large animals that eat through filters. The next step is to study how oceanographic forces create dense patches of both microplastics and prey, as well as how microplastics affect the nutritional value of key prey species for baleen whales and other economically and ecologically important ocean species.
“By using new technologies like drones, biologging tags, and echosounders, we can learn more about the basic biology of baleen whales and whale ecosystems. This helps us do important translational research in sustainability and other fields,” said Goldbogen.
Source
Matthew Savoca (2022). Field measurements reveal exposure risk to microplastic ingestion by filter-feeding megafauna, Nature Communications. DOI: 10.1038/s41467-022-33334-5.
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