Reef manta rays could ingest as many as 63 pieces of plastic per hour while feeding in the waters off Indonesia’s Nusa Penida and Komodo National Park, marine biologists say.
For whale sharks, which seasonally aggregate in East Java, it could be up to 137 pieces per hour.
That’s the rather depressing finding of a collaborative effort to estimate the extent of the plastic problem by a team from the Marine Megafauna Foundation, Australia’s Murdoch University and Udayana University, Indonesia.
Their report is published in the journal Frontiers in Marine Science.
As manta rays and whale sharks spend a lot of time feeding in inshore surface waters where trash commonly aggregates, the researchers used a plankton net to trawl for plastics in the top 50 centimetres of the water column.
Thin and bendable films from single-use bags and wrappers, as well as hard fragments, accounted for more than half of total. Around 80% were microplastics of less than five millimetres.
Manta ray faeces and vomit also tested positive for plastics, the researchers say, which means that plastics are easily ingested when filter-feeding and likely expose the animals to toxic chemicals and pollutants found in plastics while in their digestive system.
The study also found that plastic abundance was up to 44 times higher during the rainy season, with the largest seasonal effect observed off Nusa Penida, in Bali.