BANGKOK — The six men lay in red body bags, lined up on a concrete dock. The first died almost three weeks before his ship reached Thailand; the last almost made it alive but died the day before the ship docked.

They were Thai and Cambodian fishermen who had succumbed to beriberi, a disease better known for striking sailors more than a century ago. But their deaths, says a Greenpeace report released Thursday, are part of an all-too modern scourge — Thai fishing fleets operating thousands of kilometers (miles) from home in unregulated waters to dodge government oversight over illegal fishing and onboard human rights abuses.

Thailand has responded to problems in the industry by grounding its overseas fleet and ordering tracking equipment installed on the vessels.

The two ships carrying the dead had left Thailand in the first few months of 2015, according to an earlier Thai government report. They parked themselves off the coast of Madagascar, where they stayed for months. They transferred their catch to “reefers,” refrigerated cargo ships, to avoid government regulators while still getting their fish to market.

Supply ships brought the fishermen fresh food once every couple of months. But they didn’t come often enough.

An inspection found “there was no fresh food,” Thai government investigators concluded after searching one ship, the Somboon 19. “The rest of the kitchen had eggs, vegetable oil, and white rice. No fresh vegetables or meat.”

The ships ran out of fresh food weeks after each delivery, forcing the crew to subsist on fish and rice — a diet deficient in Vitamin B, the root cause of beriberi. Many began to fall ill. Subject to hours of backbreaking labor, some of the fishermen began finding it hard to breathe. Their legs swelled and their bodies went limp.

Though one ship returned to Thailand as soon as a fisherman died, the second one dumped the body in the freezer of the cargo hold and kept fishing, only returning when the navy called them home, said Cmdr. Piyanan Kaewmanee, head of a Thai navy department combating illegal fishing.

“It was gross,” he told The Associated Press in a recent interview.

The arrival of the bodies on Thai shores in January 2016 kicked up a media frenzy. Newspapers reported the fishermen had died from vitamin deficiencies.

The story of how these vessels ended up so far from home in the first place starts with Indonesia and Papua New Guinea. For decades, Thai vessels fished in their waters, splitting profits in exchange for fishing licenses.

But following an AP report last year revealing that Thai fishing boats enslaved migrants from Myanmar, Cambodia and other neighboring countries, Indonesia shut off their waters to fishing vessels from foreign countries. Papua New Guinea followed suit soon after.

Deprived of their usual hunting ground, the boats set sail for seas far from the prying eyes of governments.

“Some of these problems we’ve seen in Indonesia … are just being exported and happening somewhere else,” says Mark Dia, an oceans activist and manager at Greenpeace. “Nobody really knows what happens on these vessels.”

The Greenpeace report names some of the worst fishing boat operators, who they say send fish into the supply chain of major retailers of imitation crab and cat food. The AP has not independently verified those claims.

Greenpeace said satellite data it obtained tracked the ships as they moved toward the Saya de Malha Bank, an ecologically rich breeding ground for whales that Mauritius claims is part of its exclusive economic zone. However, it’s effectively unregulated, officials and experts say.

“To send a patrol boat to inspect them at sea is hugely expensive,” Cmdr. Piyanan said. “If it’s not urgent, it’s a rarity that we’d send a patrol boat.”

After Thailand received a “yellow card” from the European Union in April 2015, Prime Minister Prayuth Chan-ocha created the Command Center for Combating Illegal Fishing.

In December 2015, the Thai navy sent a task force to inspect 74 Thai overseas fishing vessels to enforce new permit regulations. A navy report recorded dozens of vessels that had violated labor permits and overstayed their licenses, prompting them to recall their entire overseas fishing fleet back to Thailand.

After these abuses were uncovered, the Thai navy grounded the overseas fleet and prosecuted some of the operators. Seventy of the vessels are now docked in a port an hour away from Bangkok and are being outfitted with new GPS tracking equipment; they will be allowed to sail again next year.

Navy officials say they are exploring cheaper alternatives to regular in-person inspections, including hiring observers, installing on-board cameras and seeking assistance from countries such as Somalia, Djibouti, and Madagascar. New regulations stipulate that the vessels must return to Thailand every year, instead of roaming the high seas indefinitely.

Greenpeace says more needed to be done, particularly a industry ban on transshipments, the practice of using reefers as intermediaries.

Cmdr. Piyanan said regulation will always be challenging: “Anyone that is greedy enough, they can come up with things to avoid detection to avoid control from the government.”

Story: Dake Kang