Garbage in the food chain? It’s a concern echoed over the years in several published studies, which have found plastic and other debris in the stomachs of marine mammals, seabirds and fish.
While the results of these studies are often exaggerated, all evidence points to a tangible crossing between plastic waste and the natural world, which is turning up in various parts of the ecosystem, including the deep sea, said Anela Choy, a University of Hawaii graduate student who is lead author of a study recently published in the scientific journal Marine Ecology Progress Series.
Her study found large, predatory fishes in offshore Hawaiian waters are consuming a large amount of plastic and other debris. It examined the stomachs of nearly 600 fish representing 10 predatory open-ocean species, including commercially valuable tunas and billfishes, over six years. Seven of the 10 species were found to have ingested some form of debris, with varying degrees of frequency.
Overall, 19 percent of the fish contained some form of marine debris in varying sizes and mostly some form of plastic or fishing-related line. The species that ate the greatest amount of plastic were the small-eye and big-eye opah, also known as the moonfish, which did not seem to favor a certain type of debris. This is “a delectable popular fish consumed in Hawaii and around the world,” Choy said.
Another big plastic eater was the longnosed lancetfish, which had a 30 percent debris ingestion incidence. It seemed to have a liking for white and clear plastic pieces, which could possibly be confused for the gelatinous prey they eat. While not consumed by humans, the longnosed lancetfish is commonly found in open waters and frequently caught by fishermen, Choy said.
“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,” Choy said. “Deeper water fishes may have been coming up close to the surface to ingest debris, which is an unusual and unexpected behavior.”
Another more likely reason for this find is the debris could be coming to them. Choy said 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.
Choy also mentioned a recent study by researchers at the Monterey Bay Aquarium Research Institute which revealed how trash is accumulating in the deep sea, particularly in the Monterey Canyon off California. These researchers reviewed 22 years of footage captured by deep-sea remotely operated vehicles and found more than 1,150 pieces of debris on the seafloor.
Choy admitted many questions remain following her study and more research is needed. She said the effects of plastic ingestion on fish health are still uncertain, but could include gut blockage, particularly when large pieces are consumed, and the transfer of chemical toxins. She doesn’t know how long debris stays in the stomachs of large fishes or if the fish have special enzymes that help them digest plastic. Nor does she know how many fish ate the plastic and regurgitated it or passed it out of their intestines. She can’t tell how many fish ate plastic and died or why fish ultimately consume plastic and other debris.
The study raises concerns as to whether the plastics and pollutants fish ingest can make it up the food chain, including into the seafood eaten by humans, and if there’s a threat to human health. Many plastics are known to absorb or take up PCBs, organochlorine pesticides, metals, and petroleum hydrocarbons, “some of which may desorb in acidic stomachs resulting in uptake to the animal,” the study stated.
Choy stressed the debris found in the collected fish was in their gut, which humans do not eat. She also guessed that if a risk exists, it would likely be chemical. But her study did not focus on toxins or their effects. However, her study stated, “Given the global commercial importance of (opah) and other large pelagic fishes, namely tunas and billfishes, future research might evaluate whether these fishes carry elevated chemical toxin burdens that may ultimately pose a risk to the seafood-consuming public.”
Choy’s study was based on observations collected during multiyear diet studies, the primary objective of which was to describe food habits and tropic ecology of large fish species in the region. Her co-author was Jeff Drazen, an associate professor in the Oceanography Department of UH Manoa’s School of Ocean and Earth Sciences and Technology. These observations are reportedly “the first of their kind in scope and in number,” as well as “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.” Simply put, Choy said the study illuminates the fact that plastic and other marine debris is not just a surface problem.
To read her study, “Plastic for dinner? Observations of frequent debris ingestion by pelagic predatory fishes from the central North Pacific,” go to int-res.com/articles/meps_oa/m485p155.pdf.