Shrimp and other seafood fishing is a big business in Thailand. The industry employs more than 650,000 people and annually produces more than $7 billion in exports that show up on dinner tables all over the world, including in the United States. It also has a horrific dark side. Its reliance on slave labor is so pervasive and ugly that the State Department now lists Thailand as one of the worst violators among 188 countries judged every year on how they deal with human trafficking.

The ratings were begun 14 years ago, after the United States enacted an anti-trafficking law and the United Nations adopted the Palermo Protocol. Both call for countries to criminalize trafficking, punish offenders and provide shelter and support to victims. The State Department’s annual human trafficking report, released on Friday, is an important part of this effort, systematically chronicling abuses and government efforts to stop them.

Thailand has long been a magnet for migrants from neighboring countries. These migrants now number two to three million people. Tens of thousands of them are victims of trafficking — vulnerable men, women and children, some forced into the Thai sex trade, others pushed into garment manufacturing and domestic work. Now comes growing evidence that many are also being exploited in fishing and fishing-related industries.

According to the 432-page report, men from Myanmar, Cambodia and Thailand are forced to work on Thai fishing boats that travel throughout Southeast Asia and beyond. Many pay brokers to help them find work in Thailand, and are then sold to shipowners. Under threat of jail or deportation and desperate for income, they are forced to work 18 to 20 hours a day, seven days a week, for very low wages, and are often threatened and beaten. The exact scope of this abuse is unknown but the report cited two surveys that suggested between 17 percent and 57 percent of the fishermen were treated this way.