In an interview with CNN's Andrew Stevens, Chan-ocha said his government was updating legislation to tackle the issue, which was this month highlighted by CNN's Freedom Project.
"This has been happening for a long time," said Chan-ocha. "Previous governments have tried to solve the problem, but not effectively.
"So I've had to overhaul the laws, so we can deal with the issues. The laws relating to fisheries are very outdated and must be amended so the agencies can operate effectively."
CNN's Freedom Project spoke to Thai men who had been promised decent wages on fishing boats only to find themselves among thousands of migrant workers, working as virtual slaves.
One man told CNN he spent six years on board one boat, and was made to work 20-hour days in life-threatening conditions.
His horrific journey only came to an end last month, thousands of miles from Thailand, when the boat he was on was impounded by Indonesian authorities for suspected illegal fishing.
Chan-ocha told CNN: "The situation is now severe -- we need to move more quickly."
The Thai leader said trafficking victims needed to be rehabilitated.
"The most important thing is to identify who the victims are -- and where they come from. If they come from another country we will repatriate them. But we first have to rehabilitate them until they are strong," he said.
"If they are Thais, we will provide them with training to help them get jobs. We have a ministry which has set up a program to help these victims."
Trafficking in Persons report
The issue of slavery and rights abuses in the Thai fishing industry has become acute in recent years. As the global demand for seafood has increased, the Thai economy improved, making it more difficult to attract workers to dangerous jobs on fishing boats.
Last year, the U.S. State Department downgraded Thailand to the worst possible ranking -- Tier 3 -- in its
Trafficking in Persons report. It said Thailand was a source, a transit point and a destination for trafficking.
The report also said that ethnic minorities and citizens of neighboring countries were especially at risk of exploitation in Thailand through forced labor or the sex trade.
Asked about a labor rights group's claims that some Thai officials could be deliberately avoiding registering some trafficking victims, so as not to affect the country's rating on the U.S. report, Chan-ocha said that identifying victims was "very complicated."
"We have to set up a committee to specifically look into this problem. The deputy prime minister is driving this -- it is complicated because it involves several agencies. But, no, it's not happening -- we're not disregarding the victims just because we want lower numbers."
The European Union last month called Thailand a "non-cooperating" country because of poor monitoring and control of its fishing vessels and the trade of fish and seafood from other countries into Thailand.
Unless it cracks down on the situation, Thailand faces a financially damaging embargo on its fish exports to the EU from October.
Exports by Thai seafood companies to the United States and Europe are worth around $2.5 billion annually, with Thai Union Frozen Products one of the largest -- and owner of the John West and Chicken of the Sea brands.