The Government's move to ban foreign-flagged fishing boats is being criticised for being so slow that further abuse of international crew members could occur before they are in place.

Foreign-chartered vessels working for New Zealand-owned companies and operating in New Zealand waters will have four years to reflag as New Zealand ships, requiring them to meet local requirements and standards, under a government decision announced yesterday.

Concerns about the treatment of foreign workers intensified after 32 Indonesian crew on the Korean Oyang 75 last year walked off the fishing boat alleging sexual and physical abuse.

The changes will affect the 12 out of 27 New Zealand fishing companies which use foreign-chartered ships and are expected to impact on them financially, although the Government has not conducted a cost analysis.

Primary Industries Minister David Carter said other countries, with the exception of Brazil and Namibia, had already banned foreign-flagged ships.

The Government also hoped the changes would encourage more use of New Zealand crews.

Maritime lawyer Peter Dawson said the changes were commendable but four years was too long and the boats should be required to be reflagged within two years.

''There are no interim measures to prevent abuses that are currently happening.''

Boats could easily be reflagged within a year and fisheries companies should have been prepared for the changes after having the benefit of low-cost operations for more than 20 years, he said.

''If they haven't built up the capital and resources and anticipated that this would happen, it reflects poor forward planning on the part of those companies.''

The Government aims to put ministry observers on all foreign-owned fishing vessels within the next 12 months, but Dawson said there would need to be two observers to provide 24-hour coverage.

''We've had reports that as soon as observers go to sleep, dumping and high-grading of fish occurs.''

Labour industrial relations spokeswoman Darien Fenton agreed four years was too long.

''That gives room for an awful lot of abuse.''

Maritime Union general secretary Joe Fleetwood said the four-year period was ''overly generous''.

''Given the string of fishery breaches, labour abuses and harm to crew members experienced in recent years, we must ensure that the industry is policed over the transition period.''

Sanford, which uses foreign-chartered vessels, said it had to assess its options.

Managing director Eric Barratt said the boat's owners would have to decide whether they were willing to be reflagged.

Sealord chief executive Graham Stuart said the changes would go a long way towards tidying up unacceptable practices which brought into question the reputation of New Zealand's fishing industry.

The company said it would cost it around $1m a year for the new observer regime.

The Seafood Industry Council said the four-year transition recognised there were significant legal and contractual adjustments required.

As well as the alleged abuse of its crew, the Oyang 75, along with its sister ship the Oyang 77, has been charged with illegally dumping fish overboard.

Owned by one of Korea's biggest fishing companies Sajo Oyang, the Oyang 75 was brought into New Zealand to replace the 38-year-old Oyang 70 which sank east of Otago in 2010, with the loss of six men.

The sinking revealed appalling conditions on the boats. Foreign-chartered boats catch fish worth $650 million a year, most of it for Maori iwi quota, as part of the $1.5 billion fisheries export industry.

Later in 2010, the Korean No. 1 Insung sank in the Ross Sea with the loss of 22 men.

A New Zealand joint ministerial inquiry earlier this year found Korean fishing charters were damaging New Zealand's international reputation.

The Korean Embassy has said an inter-departmental delegation would arrive in New Zealand over the next few weeks to investigate concerns with Korean-owned fishing boats.

Carter said the Ministry of Foreign Affairs and Trade yesterday briefed the Korean government on the changes.

- © Fairfax NZ News