SAMUT SAKHON/BANGKOK, Thailand (REUTERS) - Enslaved on a Thai fishing vessel for 11 years, Tun Lin saw his fellow workers lose their minds one after another, with one fisherman jumping into the sea to end his life.
Some would start murmuring or laughing to themselves as they worked day and night in Indonesian waters on the cramped boat, often surviving on fish they caught and drinking water leaking from an onboard freezer.
"It was like a floating prison - actually, worse than prison," the Burmese fisherman, who was sold into slavery, told the Thomson Reuters Foundation in Samut Sakhon, a Thai fishing hub some 40km south-west of the capital Bangkok.
The 36-year-old, who was rescued in 2015 after losing four fingers and being stranded on a remote island for years without pay, is now lobbying for fishermen's rights with the Thai and Migrant Fishers Union Group (TMFG).
Under growing consumer pressure, Thailand has introduced a raft of modern technologies since 2015 - from satellites to optical scanning and electronic payment services - to crack down on abuses in its multi-billion-dollar fishing industry.
It is one of a growing number of countries using innovation to deal with modern slavery, from mobile apps in India to blockchain in Moldova, but experts warn against over-reliance on tech as a silver bullet without stronger workers' rights.
"Technology can be a double-edged sword," said Patima Tungpuchayakul, co-founder of the Labour Rights Promotion Network Foundation, a Thai advocacy group.
"It has become an excuse the government is using to justify they have done something, but in practice they don't use it to solve the problem." More than half the estimated 600,000 industry workers are migrants, often from poor neighbouring countries such as Cambodia and Myanmar, United Nations data shows.
After the European Union threatened to ban fish exports from Thailand, and the US State Department said it was failing to tackle human trafficking, the South-east Asian country toughened up its laws and increased fines for violations.
It banned the use of workers aged below 18 and ordered fishermen to be given contracts and be paid through electronic bank transfers.
Authorities ordered Thai vessels operating outside national waters to have satellite communications for workers to contact their families or report problems at sea, plus tracking devices to spot illegal fishing.
"We are serious in law enforcement regarding human trafficking and illegal labour cases," said Weerachon Sukhontapatipak, a Thai government spokesman. "There might not be abrupt change ... it will take time."
Thailand is also rolling out an ambitious plan, using iris, facial and fingerprint scans to record fishermen's identities to make sure they are on the boats they are registered with and help inspectors spot trafficking victims.
Rights groups meanwhile have tried to use satellites to pinpoint the location of ships that remain at sea for long periods, potentially indicating enslavement.
But human trafficking expert Benjamin Smith said using satellites to tackle slavery at sea was not easy unless there is a lead on where to track in the vast ocean.
"I think people underestimate the size of the ocean and the ability to pinpoint where something as small as a boat is,"Smith from the UNOffice on Drugs and Crime (UNODC) said.
"If you have good information, intelligence, then satellite images can be good ... It has to be a small part of a much bigger effort."
Smith also highlighted difficulties prosecuting cross-border trafficking cases and maritime police funding shortages, adding that continued consumer pressure on firms to clean up their supply chains could be a potent force to help end slavery.
"That's probably the best way you can start," he said.
Fishermen remain at risk of forced labour and the wages of some continue to be withheld, the International Labour Organization (ILO) said in March.
To combat slavery, firms must improve workers' lives, rather than cutting labour costs and recruiting informally to meet demand for cheaper goods, experts say.
"Smaller owners are getting squeezed, and still rely on brokers and agents, who dupe workers and keep them ignorant of their rights and conditions on the boat," said Sunai Phasuk, a researcher with lobby group Human Rights Watch in Bangkok.
Workers are set to become more vocal with the May launch of the Fishers' Rights Network, which aims to combat abuses, backed by the world's largest canned tuna producer, Thai Union, and the International Transport Workers' Federation (ITF).
"Without enforceable rights at the workplace and the strength that comes from being represented by a union, labour rights violations and the mistreatment will continue," said Johnny Hansen, chairman of ITF's fisheries section.
Thailand's ratification this month of the ILO protocol on forced labour also offers hope. It is the first Asian country to promise to combat all forms of the crime, including trafficking, and to protect and compensate victims.
"We have ... committed to changing the law to allow workers to form unions, so we can work together to solve the problems,"said Thanaporn Sriyakul, an advisor to the deputy prime minister. "But the process is long, and it will take time."
Thailand has also pledged to ratify two other conventions on collective bargaining and the right to organise, which campaigners say would better protect seafood workers.
This would be good news for Lin's fishermen's group, which has helped rescue more than 60 people since 2015, but has no legal status as Thai law does not permit fisher unions, leading rights advocates to use other terms, like workers' groups.
"There are still lots of victims, and I want to help them,"Lin said. "As fishermen who have suffered in a similar manner, we understand each other's needs and are able to help better."