New Zealand fishing giant Sealord expects to collect a hefty premium from its organically certified mussels, a delicacy believed to be a world first.

The first batch of certified mussels are being shipped to Britain within weeks and will also be available at the Marlborough Food and Wine festival next month.

The mussels are certified by Bio-Gro - a move Sealord, the country's largest producer of mussels, says is unprecedented.

The company has spent tens of thousands preparing for certification over the last three years.

Sealord has also monitored the quality of its marine waterspace for eight years, information used when applying for the certification.

Research manager Lance Searle said certification would attract a premium and the mussels were expected to sell well in markets such as Europe and the United States.

Demand for organics in Britain is enjoying double digit growth and the premium for certification will be "significant," said Searle.

The certification comes after a disastrous year for the industry, with the value of sales to November dropping to $114 million compared to $169 million for the same period the previous year.

The drop in value was not reflected by a drop in quantity, which fell from just under 26,000 tonnes to around 23,000 tonnes in a year disrupted by global issues such as Sars.

The drop in value was largely due to the high value of the kiwi against the US dollar, where the majority of New Zealand mussels are exported.

"We need to find new ways to value add to mussels and this is a way to do it," said Searle. "We want to sell more mussels at a higher price."

Sealord can produce 6000 tonnes of organic mussels from its annual production of 18,000 tonnes.

While the initial sales for the certified mussels are likely to be small, Searle said he expected the organics to eventually be half of total output.

The certification process involves monitoring the marine farm water and a adhering to a code of practice for mussel health and welfare.

Sealord needed to prove its farms, all of which are in the Marlborough Sounds, were free from land contaminants and heavy metals, among other things.

It also has to prove the mussels are treated humanely.

The certification process had cost Sealord around $50,000 to $80,000 in staff time and would continue to cost up to $100,000 a year in for monitoring. Bio-Gro would do annual audits.

Searle said the money "could take a couple of years to recoup ... but it's a long term plan".

Bio-Gro will use Sealord's precedent as a benchmark for other mussel farmers wanting certification, although some information will remain confidential.

"This is ground-breaking stuff," said Searle.