(CNN) - The dead kept coming in 2017.
For years, the north coast of Japan had been the scene of a macabre phenomenon: fishing boats that were on the coast carrying the bodies of dead North Koreans, more than 1,000 kilometers from their homeland.
But the numbers in 2017 were unprecedented: More than 100 ships landed on the Japanese coast with 35 bodies on board. Only 66 ships had appeared the previous year.
No one could explain why so many of these so-called "ghost ships" ended up in Japan that year. A Japanese Coast Guard said it could be as simple as the weather. Others speculated that North Korea's old fishing fleet was at fault.
Since then, more of these rickety ships have massively appeared on the shore, albeit with fewer bodies. The mystery has puzzled authorities for years, but a study published Wednesday by the international non-profit organization Global Fishing Watch offers a compelling new theory. Blame the Chinese "dark fishing fleets".
The report's authors used various satellite technologies to analyze marine traffic in Northeast Asia in 2017 and 2018, and found that hundreds of Chinese fishing vessels were sailing in waters off North Korea. Chinese ships appeared to be fishing there illegally, pushing North Korea's own fleet, which is ill-equipped to travel long distances, further off the coast of North Korea and in Russian and Japanese waters.
This Global Fishing Watch chart shows the location transmitted by all vessels identified as probable fishing vessels sailing within the North Korea Exclusive Economic Zone during 2017 and 2018.
This Global Fishing Watch chart shows the location transmitted by all vessels identified as probable fishing vessels sailing within the North Korea Exclusive Economic Zone during 2017 and 2018.
Fishing in North Korean waters, or buying and selling North Korean fish internationally, is a violation of international law. Pyongyang's fish trade, worth approximately $ 300 million a year, was sanctioned in 2017 by the United Nations Security Council as part of its effort to punish the Kim Jong Un regime for its repeated ballistic missile tests this year.
But that doesn't seem to have deterred some 900 Chinese boats in 2017 and 700 the following year, according to the Global Fishing Watch report.
The non-profit organization noted that these Chinese vessels likely caught more than 160,000 metric tons of Pacific flying squid, one of the region's most valuable fishery products, in 2017 and 2018, more than South Korea and Japan combined during the same period. The estimated catch was worth more than $ 440 million.
While it is unclear whether North Korea could have made so much money fishing in its own waters, it now appears that Pyongyang was able to recoup some of its lost catch by selling fishing rights to foreign operators, likely Chinese. A United Nations report released in March claimed that North Korea earned an estimated $ 120 million in 2018 by selling or transferring fishing rights in violation of UN sanctions.
Jaeyoon Park, a senior data scientist at Global Fishing Watch and co-author of the study, said the discovered vessels comprised "about a third of the size of the entire distant water fishing fleet in China."
"It is the largest known case of illegal fishing perpetrated by vessels originating in one country that operate in the waters of another nation," he said.
With so many boats off the coast of North Korea, the country's own fishing fleet was ousted, forced to sail further offshore to find its catch, and the consequences were deadly, according to Jungsam Lee, another study collaborator. .
"It is too dangerous for them to work in the same waters as the Chinese trawlers," said Lee. "That is why they are pushed to work in Russian and Japanese waters and that explains why some of North Korea's damaged ships appeared on the beaches of Japan."
Park and the other experts explained that they were able to track these ships using new satellite and radar technologies that were not available in previous years. Open source intelligence NGOs and nonprofits increasingly use these resources to analyze shipping traffic in hopes of finding or better understanding the tactics used to evade sanctions.
Global Fishing Watch reported in a statement that boats that illegally fish in North Korean waters are believed to be owned and operated by "Chinese interests" because that is where they were located. However, ships involved in illicit activities in these waters, whether to move goods at sea to avoid prying eyes of customs officials or to dredge sand, often lack proper documentation, making it more difficult for them. to track.
CNN has contacted the Chinese Foreign Ministry for comment.
Chinese ships are sheltered from bad weather in the port of Sadong on the island of Ulleung in South Korea on November 11, 2017.
A sustainability problem
The waters of Northeast Asia are some of the most opaque and disputed seas by fisheries in the world. China, Russia, Japan and the two Koreas are involved in some kind of territorial dispute between them.
Fish stocks have declined dramatically in recent years, another major problem that the parties have been unable to solve. Pacific flying squid stocks have fallen 80% in South Korean waters and 82% in Japanese waters since 2003, according to Global Fishing Watch.
"While fishermen and their families have seen their incomes drop, academics are baffled by the most likely cause of this decrease in catch. Many point out that overfishing is the biggest culprit, while some suggest that climate change may be playing a role, with changes in water temperature affecting spawning and migration patterns. It seems depressing but too familiar, ”Park wrote in a blog post accompanying the study.
Fishing sustainability is a major problem across the planet. Money and jobs in trade-dependent coastal communities are depleted and fueled an increase in piracy in places where the fishing industry cannot depend on a functioning coast guard, such as Somalia.
Experts like Park believe that although Japan and South Korea have worked independently to make squid fishing more sustainable, “the absence of multilateral cooperation and the exchange of information between all the countries involved in this cross-border fishing means that it is impossible to obtain a solid science and a regional management plan for the stock ”.
South Korea's Ministry of Oceans and Fisheries says it reviews the findings, while Masanori Miyahara, president of the Japan Fisheries Research and Education Agency, said in a statement accompanying the Global Fishing Watch study that the lack of data Sharing is "a great challenge considering the critical importance of squid in the region."
"Illegal fishing in these waters is a very serious matter in Japan," said Miyahara.
Park said his team's investigation has highlighted a "fundamental failure in the proper and transparent management of a shared resource" and that there is "an urgent need for cooperation between the countries involved in this fishery."
CNN's Junko Ogura and Yoonjung Seo contributed reporting
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