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An estimated five million tonnes of debris was swept out to sea during Japan’s 2011 Tōhoku earthquake and tsunami—five million tonnes of houses, cars, boats, fishing gear, shipping containers, and other materials. It was a catastrophic loss of property to add to the 18,500 dead. But where did all of this debris go? Beachcombers along the west coast of Canada and the United States reported finding fishing equipment, crates, and even whole boats in the years after the tragedy, but no one knew exactly how much had washed ashore. Now, a new study has found that the tsunami increased marine debris along North American coastlines by ten times.
“We’d had anecdotal reports from people living along shorelines saying, ‘This is outside what we’ve ever experienced.’ Just huge amounts [of debris] that have not been seen before,” says Cathryn Murray, a marine ecologist and lead author of the study. “It was good to put a number to that.”
Researchers used data from the US National Oceanic and Atmospheric Administration’s existing marine debris monitoring program, which compiles results from more than 1,100 surveys at 120 sites along the west coast of North America and Hawai‘i. Those surveys showed that approximately 100,000 items washed up on the monitored beaches from 2012 to the end of 2015, and that the rate of this influx spiked 16 months after the disaster. Hawai‘i received the most debris, while British Columbia—particularly the northern islands of Haida Gwaii—got the second most.
The team also drew on long-term data collected by volunteers in the Olympic Coast National Marine Sanctuary, in northern Washington, to compare debris arrivals before and after the tsunami, finding that the rate increased tenfold after 2013.
Ultimately, the distribution of debris matched patterns predicted by oceanographic models, says Murray, who worked for the North Pacific Marine Science Organization during the study.
More than just putting a tally on the devastation, the data could help governments respond to and plan for future disasters, says Kirsten Moy, a marine biologist with the Hawaii Coral Reef Initiative who served as the marine debris coordinator for the state from 2015 to 2016.
Like other communities, Hawai‘i was largely unprepared for the tsunami debris, which included more than 60 Japanese fishing vessels. The state had to remove and dispose of the items, but also be on the lookout for potential invasive species. Moy recalls investigating a jet ski picked up on a Hawai‘ian beach that was full of mussels, clams, and even a crab. “It was like a little Noah’s ark traveling across the Pacific,” she says.
Murray says invasive species ecologists around the world took notice when the first large tsunami items began arriving with kelp, crustaceans, sea stars, and other stowaways. They were surprised those nearshore species survived a two-year journey across the open ocean.
“We don’t know a lot about what that will mean for the future—will species be able to use plastic to move around the ocean?” Murray says. “This major event gave us a snapshot.”