News about the marine plastic problem isn’t very uplighfting these days. The first scientific results from Scripps Institution of Oceanography at University of California San Diego (UCSD) offer a bleak view of an area of the ocean that has been dubbed as the “Great Pacific Garbage Patch.”
Peter Davison and Rebecca Asch with the Scripps Environmental Accumulation of Plastic Expedition (SEAPLEX) discovered plastic waste in more than 9% of the stomachs of fish collected in the North Pacific. They looked at 141 fishes from 27 different species. The scientists estimate that fish in the intermediate ocean depths in that region of the Pacific Ocean ingest plastic at a rate of roughly 12,000 to 24,000 tons per year.
The North Pacific Subtropical Gyre, where SEAPLEX researchers did their work, has not been thoroughly analyzed by scientists. There are many questions about marine debris in the area and its effects. Instead of a visible “patch” or “island” of trash, the North Pacific Subtropical Gyre has marine debris dispersed across thousands of miles. The debris area can’t be mapped from air or space, so SEAPLEX researchers tried to map the boundaries of the patch by sampling 132 net tows (of which 130 came with plastic) over a distance of more than 2,375 kilometers (1,700 miles).
The analyses of the fish were sobering. The plastic debris was mainly chips of plastic that were smaller than a human fingernail. Davison and Asch say the majority of the stomach plastic pieces were so small that they couldn’t figure out their origin.
According to a UCSD press release:
‘About nine percent of examined fishes contained plastic in their stomach. That is an underestimate of the true ingestion rate because a fish may regurgitate or pass a plastic item, or even die from eating it. We didn’t measure those rates, so our nine percent figure is too low by an unknown amount,’ said Davison.
The authors say previous studies on fish and plastic ingestion may have included so-called ‘net-feeding’ biases. Net feeding can lead to artificially high cases of plastic ingestion by fishes while they are confined in a net with a high concentration of plastic debris. The Scripps study’s results were designed to avoid such bias. The highest concentrations of plastic were retrieved by a surface collecting device called a ‘manta net,’ which sampled for only 15 minutes at a time. The short sampling time minimizes the risk of net feeding by preventing large concentrations of plastic from building up, and also by reducing the amount of time that a captured fish spends in the net. In addition to the manta net, the fishes were also collected with other nets that sample deeper in the water column where there is less plastic to be ingested through net feeding.
The study focused on the prevalence of plastic ingestion, so it didn’t look at the toxicological impacts on fish and the composition of the plastic debris.
Most of fish analyzed in the study were lanternfish. They are important in the food chain because they connect plankton, which are at the bottom of the food chain, with animals at the higher levels of the food chain. How the ingestion of plastic by lanternfish affects animals along the food chain needs to be investigated.
The SEAPLEX voyage set off in the summer of 2009. You can watch a YouTube video describing the expedition:
Source: “Scripps Study Finds Plastic in Nine Percent of ‘Garbage Patch’ Fishes,” Scripps News, 06/30/11
Source: “(Narrated) Footage from SEAPLEX Voyage to the Great Pacific Garbage Patch,” YouTube
Image by J. Leicther, with no usage restrictions; used under Fair Use: Reporting.
Rajendrani "Raj" Mukhopadhyay is a science writer and editor who contributes news stories and feature articles on scientific advances to a variety of magazines. Raj holds Ph.D. in biophysics from Johns Hopkins University.