Researchers have confirmed that even mesopelagic fish, normally found at 200 to 1,000 metres' depth, have ingested microplastics.
Recent research has found microplastics in nearly three-quarters of the mesopelagic fish caught in the northwest Atlantic.
Typically found at depths of 200 to 1,000 metres, mesopelagic fish are a major food source for many marine animals, like tuna, swordfish, dolphins, seals and even seabirds. They remain in deeper waters during the day, and swim to the surface at night to feed.
"These fish inhabit a remote area, so theoretically they should be pretty isolated from human influences, such as microplastics. However, as they regularly migrate to the surface, we thought that they may ingest microplastics there," said lead author of the study, Alina Wieczorek from the National University of Ireland, Galway.
To find out more, Wieczorek and her colleagues conducted research in which they caught mesopelagic fish at different depths and examined their stomach contents. A specialised air filter was used to exclude airborne plastic fibres from the lab.
What they found was a wide array of microplastics in the fish stomachs - in 73 percent of the fish they caught. According to Wieczorek, they recorded one of the highest frequencies of microplastics among fish species globally, adding, "In particular, we found high levels of plastic fibers such as those used in textiles."
"The high ingestion rate of microplastics by mesopelagic fish that we observed has important consequences for the health of marine ecosystems and biogeochemical cycling in general," Wieczorek added.
The team will conduct further studies to find out whether the fish consume the microplastics directly, or whether they ingest them through the consumption of prey animals that have previously consumed the microplastics.