The Oyang 75: a Korean fishing boat whose crew walked off in Lyttelton in 2011 amid claims of assault, sexual assault and unpaid wages.

Indonesian fishermen working on boats in New Zealand waters face slave-like conditions, violence and sexual abuse, a report says.

The Auckland University research, based on interviews with 300 fishermen, found they were forced to work days on end, with shifts ranging from 16 to 53 hours for as little as 49 cents an hour. They faced physical violence and debt entrapment.

Some crew were forced to eat rotting fish bait to survive, the report says.

The work conditions on some boats – mostly owned by Korean companies chartered by New Zealand firms – meet international criteria for slavery, forced labour and trafficking.

One worker told the researchers:

"After working long shift, I was very sleepy and slipped down stairs, so I reached out to steady myself but touched a Korean officer. He punched me in the back of my head, then punched me another six times in the face. My nose was bleeding, eyes very painful, head really hurt. Swollen face, one eye bleeding and could only see blurry."

Ship's officers held absolute power over their floating empires – using physical threats, withholding payment and exhausting work practices to maintain control, the report says.

On the all-male boats, rape and sexual assault of crew members was commonplace.

One crewman spoke of a workmate being raped by officers on the bunk below him.

Another man gave an account of being raped by an officer below deck.

"Suddenly, [the officer] came and tried to kiss me. I tried to stop his body pushing up against mine to the point that I fell I couldn't stand it and I felt repulsed and disgusted . . . he kept pushing it on to me."

Escaping ships is difficult. Many men had gone into debt with recruiters, offering their homes as collateral for unfulfilled contracts.

One worker walked off his ship in New Zealand after being beaten and sexually abused by officers. Deserting had disastrous consequences for his family.

To get the job, he paid an agent in Indonesia more than $4000 in recruitment fees and forfeited three months' wages as collateral, signing off liability to his brother.

His desertion placed his family in debt bondage for six years. His brother was fined $15,000 and the court seized his house until the fine was paid.

Ships sailing in New Zealand waters are covered by local employment law but none of the workers in the study received the New Zealand minimum wage, the report says. The researchers found that, on average, crew members earned between $6700 and $11,600 each a year.

More than 500 workers have escaped the ships in New Zealand and tried to take legal action in the past five years but none have been granted compensation or wage settlements.

Back in Indonesia, they go back to scraping a living off the sea and hope to forget about what happened to them here.

"We don't talk to each other about it. We try to forget," one worker said.

Auckland University researcher Glenn Simmons said hearing the fishermen's stories was "absolutely gut wrenching".

"There's no question that our system has failed these men," Simmons said.

The long timeframes for employment disputes meant non-residents could not afford the process, he said.

The Government announced a ministerial inquiry into foreign charter vessels (FCVs) in 2012 and followed up with a law-change insisting all FCVs had to be flagged to New Zealand and covered by New Zealand labour law.

Labour's primary industries spokesman Damien O'Connor said there were loopholes. The Department of Labour was too stretched to effectively enforce their own legislation, he said.

"We need fast-track provisions to enable these workers to get fair treatment and return home. Now, they are left in limbo for months and months, which is completely unjust and inhumane."

A spokeswoman for the Ministry of Business, Innovation and Employment said it took "the exploitation of workers very seriously" and was working hard to stop the practice.

Simmons said the New Zealand response to problems on fishing boats was poorly co-ordinated, with police, Department of Labour, Ministry for Primary Industries and Maritime NZ working to different briefs.

New Zealand firms that chartered Korean fishing boats should know of the conditions on board, he said.

"They may not have known the seriousness of what they were looking at but they knew there were problems on these vessels."

Simmons said many of the men were deeply traumatised and carried the guilt of being unable to stop abuse of their crewmates.

"They have to go through life now, living with the horrors that befell them in New Zealand," he said.