Hawaii's predatory fish are eating plastic (and we are eating them...)

opah or moonfish photo
CC BY-NC-ND 2.0 Owen and Aki

University of Hawaii, Mãnoa, reports on a recent study that shows just what big fish are having for dinner. And it includes more plastic than we ever thought before.

The university reports, "Over a six-year period, researchers investigated the stomach contents of 595 fish representing 10 predatory open-ocean species, including commercially valuable tunas and billfishes. Seven of the 10 species were found have ingested some form of debris, with varying degrees of frequency."

Looking at two different species of opah (moonfish), which is commonly eaten around the world, researchers found that 58% of small-eye opah and 43% of big-eye opah had eaten some kind of plastic debris. Additionally, 30% of longnosed lancetfish, a fish commonly caught but not eaten by humans, had eaten debris, indicating that fish all along the food chain are ingesting some form of plastic pollution.

“What was most surprising was that the fish that most frequently ingested debris are all thought to be deeper water species, generally those that live beneath the sunlit upper 500 to 600 feet of the water column,” says Anela Choy, a UH Mānoa graduate student and lead author of the study, in the university press release.

This could mean that deeper water fish are coming up to the surface to eat debris, or it could be that plastics are sinking down to them, which can happen as pieces are colonized by algae and biofilm and get heavier.

From Hawaii News Now:

"A lot of the plastic we found in the opah especially was white or clear in color we thought that they are maybe, possibly confusing the pieces with prey," said Choy.

It might be comforting to know that various tunas, mackerel and swordfish had very little to no debris found in their stomachs. Seven of the 10 fish studied didn't eat much plastic at all. So why do some fish eat it and others don't?

"Lancetfish and opah they tend to gravitate toward gelatinous fish to prey upon. Perhaps tuna not so much they more kind of chase their prey," said Lesley Jantz, Fishery Biologist, NOAA fisheries observer program.

So does that mean we should eat more tuna and less opah? Not necessarily but the fact is we don't know.

The plastic debris in the study is of the more obvious kind, as the pieces in the stomachs of fish were large enough to be identified. But a concern of many scientists is the fact that much smaller pieces of plastic are ingested by smaller fish, which are eaten by medium fish, which are eaten by larger fish, which are eaten by us. So just exactly how we are consuming plastic might not be as obvious. For example, plastic microfibers are released into the waterways when we wash our clothes, and small microbes at the base of the food chain are now known to feast on plastic. Researchers have also known for awhile now that microbeads found in exfoliating soap that are washed down our drains find their way into fishes' stomachs, and those fish are eaten by other animals. A few major manufacturers are only just now phasing out plastic microbeads from products, which will take years. So we know that plastic has already entered the food chain to some degree. We just don't know the full impact, or what it means to us as eaters.

Indeed, the University of Hawaii study comes to a rather obvious conclusion: "These observations are the first of their kind in scope and in number, and they suggest that more attention should be given to marine debris in subsurface waters, as well as to the potential food web implications for human consumption."

More attention definitely needs to be given to both issues, since we still do not know how human health is affected by eating fish that have eaten plastic and the chemicals in the plastics. For now all that's known is that the plastic problem is still spreading.

Hawaii's predatory fish are eating plastic (and we are eating them...)
Big fish are eating plastic, and we're eating those big fish. It's yet more evidence that plastic has entered the food chain and is making its way up to us.

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