FOR millennia the Tsushima current running north-eastward up the west coast of Japan has brought abundance to fishermen. More recently it has brought less welcome rubbish, as well as giant jellyfish grown monstrous on the effluence from the industrial revolutions taking place in China and South Korea. Now the current is giving up perhaps its grimmest cargo yet: rickety boats filled with corpses. Since October over a dozen vessels have been found drifting in Japanese waters. The latest, recovered on December 6th off the coast of Aomori prefecture in Japan’s north-east, contained four badly decomposed bodies. It brings the death toll from the ghost boats to 25.

Japan’s coastguard will not speculate on the boats’ origin, but everything—including their wooden build and primitive, flat-bottomed design, as well as cigarette packets found on board—points to reclusive North Korea. The bodies have been cremated, unclaimed and unnamed.

They were probably fishermen for squid, who were caught out in storms and who died of exposure or thirst. Fishermen in Fukui prefecture in north-central Japan say that a capsized vessel found about 100 kilometres (62.5 miles) off the coast last month had only primitive gear for catching squid and lacked even a VHF radio. “It’s incredible that it got this far,” says Mitsumasa Sakashita, one of the fishermen.

Little happens in North Korea without the say-so of the young dictator, Kim Jong Un, and the ghost vessels may attest to that. He has pushed the state-owned seafood industry to increase its haul. Seafood is North Korea’s sixth-biggest export. Running the business has long been in the gift of the army. It ensures that troops are fed first, and that the army earns hard cash—seafood exports to China, especially of crab and clams, were $67m in 2012, according to the South Korean government. That is not much by the standards of any normal country, but a fortune in North Korea. A power struggle for control of the North’s fisheries is thought by some to have led to the downfall and execution in late 2013 of Kim Jong Un’s uncle, Jang Sung Taek.