Oceanographers call it the North Pacific Subtropical Gyre. But headline writers have dubbed the remote area the “garbage patch” due to debris carried in by converging currents. Now, information gathered by a research cruise is giving new meaning to the term “trash fish,” suggesting that fish in the patch are eating up to 24,000 tons of plastic a year.
Despite its name, the oceanic garbage patch isn’t obvious to the naked eye – or even satellite sensors. Instead, the marine debris is highly dispersed across thousands of miles of ocean, and mapping the patch requires systematic sampling cruises – such as the SEAPLEX cruise launched in August 2009 from the Scripps Institution of Oceanography at the University of California, San Diego. A team of Scripps graduate students traveled more than 1,000 miles west of California to the eastern sector of the Gyre. Then, over 20 days, they collected fish specimens, water samples and marine debris at depths ranging from the sea surface to thousands of feet down.
Not surprisingly, they found trash: 130 of 132 net tows made over a 1,700 mile route contained plastic debris. And some fish, it turned out, were ingesting that trash, Peter Davison and Rebecca G. Asch of Scripps report in Marine Ecology Progress Series. They dissected 141 fish from 27 mid-water species, and found that 9.2% had plastic debris in their stomach contents — primarily broken-down bits smaller than a human fingernail. Most of the pieces were so small their origin could not be determined.
It’s likely the fish are actually ingesting more plastic, Davison says. The 9.2% figure “is an underestimate… 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,” he says. Overall, the researchers estimate that fish in the intermediate ocean depths of the North Pacific are ingesting plastic at a rate of 12,000 tons to 24,000 tons per year.
The majority of fish examined in the study were myctophids, commonly called lanternfish because of their luminescent tissue. Researchers believe lanternfish use luminescence for several purposes, including counter-illumination (thwarts predators attempting to silhouette their prey against sunlight), mate attraction and illumination of prey. The fish typically stay 200- to 1,000-meters (650- to 3,280-feet) down during the day and swim to the surface at night.
“These fish have an important role in the food chain,” Asch notes. The ingested plastic has “potential impacts,” she adds. But understanding “what those impacts are will take more research.” – David Malakoff | June 30, 2011
Source: Davison, P., & Asch, R. (2011). Plastic ingestion by mesopelagic fishes in the North Pacific Subtropical Gyre. Marine Ecology Progress Series DOI: 10.3354/meps09142
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