One of a dozen wooden fishing vessels washing up on the coast of Japan with corpses on-board. Picture: Kyodo News via AP

The origins of the boats themselves — mostly fishing vessels — are a mystery, but it’s their cargo that has Japanese officials scratching their heads and searching for answers.

Over three months, 12 boats have drifted towards the Japanese coastline and been intercepted and towed to shore. On-board, officials have discovered the lifeless, decomposing bodies of 25 men.

Bad weather can’t be blamed: Japan’s meteorological agency said there hadn’t been any since October when the boats first started washing up.

The bodies, though decomposed, do not appear to show signs of a struggle, either. Clues are few and far between, but authorities say one clue could break the mystery wide open.

On one of the boats they found a tattered cloth that appeared to have originally been part of the North Korean flag. On another boat there was a handwritten sign identifying the vessel as belonging to unit 325 of the North Korean army, though Pyongyang has made no comment on the matter.

The best and most plausible answer so far came courtesy of academics from within the region. They say the deaths can be blamed on one thing: Fisherman taking greater risks to meet the increasingly unrealistic demands for produce from Kim Jong-un.

A tiny North Korean fishing vessel is dwarfed by a North Korean coast defence ship off North Korea’s Hwanghae province.Source:News Corp Australia

The theory was, fishermen went further out to sea to catch more fish, got lost and either starved to death or died from exposure to the cold.

Kim Do-hoon, a professor of fisheries science at Bukyong National University in Busan, told the Guardian more boats were operating because the supreme leader had asked for it.

“Kim Jong-un has been promoting the fisheries, which could explain why there are more fishing boats going out,” he said.

“But North Korean boats perform really poorly, with bad engines, risking lives to go far to catch more. Sometimes they drift and fishermen starve to death.”

An Chan-il, who served in the North’s army as a junior officer before defecting to South Korea in 1979, agreed.

“Kim Jong-un is pushing hard to produce more fish. So these boats must have been stranded after overworking,” he said.

October marks the start of prime fishing season for squid, sandfish and king crab off the North Korean peninsula. In a country where millions struggle to find enough food to feed themselves, fishing is one of the country’s most important trades.

Kim’s focus on fisheries was ramped up in May when he toured fish farms and announced publicly his country’s renewed focus on food production. The visit coincided with an unusually dry winter, one which made food production increasingly difficult.

North Korean leader Kim Jong-un stopped by a fishery station in August. Picture: KCNA via AFP.Source:AFP

The most recent discovery of a mystery boat took place in late November. The vessel, according to Japanese television station NHK, was discovered floating in rough waters in the Sea of Japan, a body of water that divides Korea and the Japanese mainland.

Seven bodies were found aboard. The Friday before in a neighbouring prefecture, 10 bodies were found on three wooden ships.

Not everybody is convinced the vessels belong to fishermen. Another theory is that defectors fleeing Kim’s dictatorship found themselves in trouble and ill-equipped to handle the journey to Japan.

“(The ships) are made of wood and are old and heavy,” maritime expert Yoshihiko Yamada told NHK, adding that they resembled those used by defectors.

“They can’t travel very fast and the engines are not powerful enough to turn the ships against the currents.”

North Korea is remaining silent about the whole affair, despite the vessels carrying North Korean paraphernalia.

Japanese media reported the country’s leader was pictured on North Korean TV inspecting a fishery office on Wednesday. In the footage, Kim Jong-un reportedly flashes a wide smile for the camera. In front of him is a pile of fresh fish.