The study, which was commissioned by the DLNR and the North Pacific Marine Science Organization, aimed to determine how much debris from the Tohoku earthquake and tsunami, which struck Japan in 2011 and is perhaps most famous for triggering the Fukushima nuclear disaster, was washing up on Hawaiian shores. Debris from the tsunami has turned up throughout the Pacific over the past few years, and the new survey was intended to serve as part of a wider effort to investigate the ecological effects of tsunamis.

Between August and November 2015, researchers conducted surveys by plane, using mapping software to identify debris along the shorelines. Although the researchers didn’t walk along the shore examining debris by hand, they achieved a high image resolution from their flights, at about 2 centimeters per pixel. They classified each bit of debris by size, with the largest bits having an area greater than two square meters — about 21 square feet — and the smallest ones being less than half a square meter, or about 5 square feet.

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The survey found that very little of the debris on the Hawaiian coastline was associated with the 2011 tsunami. In fact, most of it seemed to be ordinary garbage carelessly tossed away by humans.

Altogether, the island of Niihau suffered the most, with nearly 8,000 pieces of debris identified along its shores, 46 percent of which was plastic. Most of the shoreline had a trash density of anywhere from one to 175 bits of debris per square mile, and the majority of the debris spotted fell into the smallest size category.

The island of Molokai was the runner up, with nearly 3,000 bits of debris. Oahu, on the other hand, fared the best, with just 984 bits of debris identified by the survey — although a whopping 63 percent of it was made of plastic.

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Although the density of trash on the beach is almost certainly worse in other places, the biggest takeaway from the survey is that plastic accounted for so much of it. All in all, plastic accounted for 47 percent of the debris identified on the Hawaiian shorelines. Other objects found include buoys and fishing lines, tires, foam and other bits of wood, metal, and fabric.

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Plastic pollution in the oceans is a rising concern among environmentalists because of the serious harm it can cause to marine organisms. Plastic debris is frequently found tangled up in the stomachs of birds who mistook it for food or wrapped around the bodies of drowned sea turtles and other swimming animals.

One of the biggest concerns in recent years has been the issue of microplastics — these are tiny bits of plastic, less than 5 millimeters in diameter. The problem with plastic is that it doesn’t decompose in the way that organic material does. Instead, when it’s dumped into the ocean or other bodies of water, it tends to break down over time into smaller and smaller pieces. These tiny bits of plastic can easily be mistaken for food by birds, small fish or filter feeders, such as clams and sea cucumbers.

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This is bad enough, as plastic obviously carries no nutritional value for the animals who eat it — but certain types of plastics are also known to pick up other types of chemical contaminants in the water, making them especially toxic. Scientists suspect that they might then leach these toxins into the bodies of animals who consume them. So far, there’s been a major lack of research on the ecological effects of microplastics, but recent studies have suggested that they might bring about reproductive problems in oysters, reduce survival in baby fish and cause a variety of similar complications in other shellfish, marine worms and even algae.

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Altogether, research has suggested that millions of metric tons of plastic make their way into the oceans each year. And a report earlier this year from the World Economic Forum predicted that plastic in the oceans might outweigh fish, pound for pound, by the year 2050.

The findings on the Hawaiian islands are just the latest symptom of the world’s plastic problem. In a statement on the survey’s findings, Hawaii’s DLNR Chair Suzanne Case said: “Hawaii is recognized around the world for our beautiful beaches. Unfortunately we cannot say they are pristine, because they’ve been so seriously impacted by our trash.”

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And it’s not necessarily just trash that’s been generated by people on the Hawaiian islands, either. The report points out that Hawaii is in a part of the Pacific strongly affected by a system of rotating ocean currents known as the Central Pacific Gyre, which is fed by currents stretching from Japan to California.

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“Because a circulating body of water collects debris in its center, the coastlines of Hawaii receive significant quantities of debris each year,” the report notes. The survey found that much of the resulting debris tends to wash up on the islands’ northern- and eastern-facing shores.

The report adds that the debris problem could threaten human health by creating obstacles for boating and other forms of recreation. And, ultimately, it could have major detrimental effects on Hawaii’s economically important tourism industry. But perhaps most important, the findings highlight what many scientists and conservationists are citing as an increasingly alarming environmental problem — one that could have far-reaching consequences on marine ecosystems for years to come.

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