SAMUT SAKHON, Thailand - Poor migrant workers and children are being sold to factories in Thailand and forced to peel shrimp that ends up in global supply chains, including those of Walmart and Red Lobster, the world’s largest retailer and the world’s largest seafood restaurant chain, an Associated Press investigation found.

At the Gig Peeling Factory, nearly 100 Burmese laborers were trapped, most working for almost nothing. They spent 16 hours a day with their aching hands in ice water, ripping the guts, heads, tails and shells off shrimp. One girl was so tiny she had to stand on a stool to reach the peeling table. Some workers had been there for months, even years. Always, someone was watching.

“They didn’t let us rest,” said Eae Hpaw, 16, her arms a patchwork of scars from shrimp-related infections and allergies. “We stopped working around 7 in the evening. We would take a shower and sleep. Then we would start again around 3 in the morning.”

More than 2,000 trapped fishermen have been freed this year as a result of an ongoing Associated Press investigative series into slavery in the Thai seafood industry. The reports also have led to a dozen arrests, millions of dollars’ worth of seizures and proposals for new federal laws.

Pervasive human trafficking has helped turn Thailand into one of the world’s biggest shrimp providers. Despite repeated promises by businesses and government to clean up the country’s $7 billion seafood export industry, abuses persist, fueled by corruption and complicity among police and authorities. Arrests and prosecutions are rare. Raids can end up sending migrants without proper paperwork to jail, while owners go unpunished.

“I was shocked after working there a while, and I realized there was no way out,” said Tin Nyo Win, 22, another former Gig factory worker, who routinely peeled 175 pounds of shrimp with his wife for just $4 a day.

Hundreds of shrimp-peeling sheds are hidden in plain sight in Samut Sakhon, an hour outside Bangkok, some with slaves locked inside. Last month, AP journalists followed and filmed trucks loaded with freshly peeled shrimp from the abusive Gig shed to major Thai exporting companies. They also traced similar connections from another factory raided six months earlier, and interviewed more than two dozen workers from both sites. In all, several companies received tainted shrimp, including Thai Union, one of the world’s biggest seafood companies, and a subsidiary.

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The farmed shrimp can mix with different batches of seafood as it is packaged, branded and shipped, making it impossible to determine where any individual piece was peeled. But because at least some of the Thai exporters’ shrimp was processed by forced labor, all of it is considered associated with slavery, according to United Nations and U.S. standards.

U.S. customs records show the shrimp made its way into the supply chains of major U.S. food stores and retailers such as Walmart, Kroger, Whole Foods, Dollar General and Petco, along with restaurants such as Red Lobster and Olive Garden. It also entered supply chains for some of America’s best-known seafood brands and pet foods, including Chicken of the Sea and Fancy Feast. AP reporters went to supermarkets in all 50 states and found shrimp products from supply chains tainted with forced labor.

Import and export records from Europe and Asia are confidential, but the Thai companies receiving shrimp tracked by the AP all say they ship to those continents. AP reporters in England, Germany, Italy and Ireland found several brands sourced from Thailand in supermarkets in those countries.

The businesses that responded to AP’s findings condemned the practices that lead to these conditions. Many asked for details and said they were launching investigations.

“I want to eliminate this,” said Dirk Leuenberger, CEO of Aqua Star, a leading seafood suppler. “I think it’s disgusting that it’s even remotely part of my business.”

Walmart, Red Lobster and other companies said they strive to ensure the shrimp they receive is not tainted by slavery.

“As the world’s largest seafood restaurant, we know the important role we play in setting and ensuring compliance with seafood industry standards, and we’re committed to doing our part to make sure the seafood we buy and serve is sourced in a way that is ethical, responsible and sustainable,” Red Lobster said in a statement.

Red Lobster, Whole Foods and H-E-B Supermarkets were among the companies that said they were confident — based on assurances from their Thai supplier — that their particular shrimp was not associated with abusive factories. That Thai supplier admits it hadn’t known where it was getting all its shrimp and sent a note outlining corrective measures to U.S. businesses demanding answers last week.

Responding to U.S. business demands for answers to AP’s findings, Thai Union CEO Thiraphong Chansiri acknowledged “that illicitly sourced product may have fraudulently entered its supply chain.”

Susan Coppedge, the U.S. State Department’s new anti-trafficking ambassador, said problems persist because offenders aren’t held accountable — though the United States itself hasn’t punished Thailand, an important Southeast Asian ally. She said American consumers “can speak through their wallets” by avoiding slave-produced products.

Thailand passed laws this year to crack down on fishing-industry abuses and is working to register undocumented migrant workers, who often are lured from home by brokers with promises of good-paying jobs. They are then sold to shrimp sheds such as the Gig factory, where Tin Nyo Win and his wife learned they would have to work off what was considered their combined worth: $830, an insurmountable debt.

“There have been some flaws in the laws, and we have been closing those gaps,” said M.L. Puntarik Smiti, the Thai Labor Ministry’s permanent secretary.

Critics argue, however, that changes have been largely cosmetic. Former slaves repeatedly described how police took them into custody and then sold them to agents who trafficked them again. They say police are paid to look the other way and that officers frequently do not understand labor laws.

Tin Nyo Win escaped the Gig factory and was helped by a labor rights group, which pressured authorities to act. On Nov. 9, dozens of officers and military troops burst into the shed. Frightened Burmese workers huddled on the dirty concrete floor. One young mother breast-fed a 5-month-old baby, while children were taken to a corner.

But no one at the shed was arrested for human trafficking. Instead, migrants with papers, including seven children, were sent back there to work. Ten undocumented children were taken from their parents and put into a shelter. Twenty-one other illegal workers were detained, including Tin Nyo Win and his wife, but all have since been moved to government shelters for human-trafficking victims.

Local authorities have been ordered to reinvestigate the factory, which is now closed. Police said workers were moved to another shed linked to the same owners. A Gig owner reached by phone declined to comment.

Meanwhile, the AP informed labor rights investigators who work closely with police about another shed where workers said they were being held against their will. It is being examined.