HONOLULU — Large, predatory fishes from offshore waters around Hawaii — including those from the deep, dark ocean — have been ingesting a surprisingly large amount of plastic and other marine debris, according to a new research by scientists at the University of Hawaii at Manoa.
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.
“One of the species we looked at is opah, or the moonfish, a delectable and popular fish consumed in Hawaii and around the world,” said Anela Choy, a UH Manoa graduate student and lead author of the study. “In the two species found in Hawaiian waters, 58 percent of the small-eye opah and 43 percent of the big-eye opah had ingested some kind of debris.”
These findings were based on peeking into the stomachs of nearly 140 opah. But those were not the only fish. 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, according to the study recently published in the scientific journal Marine Ecology Progress Series.
The study was based on observations collected during multi-year diet studies, the primary objective of which was to describe food habits and trophic ecology of large fish species in the region, according to Choy and co-author Jeff Drazen, an associate professor in the Oceanography Department of UH’s School of Ocean and Earth Sciences and Technology.
From sea birds to turtles to small fish, and even to bottom-dwelling echinoderms like sea cucumbers, many types of marine animals are known to ingest marine debris.
Or the debris could be coming to them. Buoyant plastics are known to sink into the deep ocean when waterlogged or perhaps weighted down by algae or encrusted by small sea animals. Wind-driven ocean mixing or water currents could also possibly transport debris to deeper waters, UH reports.
The effects of plastic ingestion on the health of these predatory fishes remain uncertain.
Researchers don’t know how long debris stays in the stomachs of large fishes, or whether they are able to pass such debris. Many plastics are known to absorb or take up PCBs, organochlorine pesticides, metals and petroleum hydrocarbons from sea water.
However, it is not known whether the toxins are transmitted to the fish that consumes the plastic, or ultimately to humans who consume the fish.