A herpes virus is identified as the agent responsible for killing about half the young oysters at farms in the Eastern Bay of Plenty.

The Ohiwa Oyster Farm was struck on November 19/20 says owner Rick York.

'The virus went through on my farm Monday a week ago,” says Rick. It hit my place; she's nailed a fair amount of the stock for next year – it's dead serious.

While it's killing the spat, the virus is not affecting public health, says Rick. The oysters are still quite edible.

'However, there's going to be a huge shortage throughout the country next year.

'We may not be able to catch this season for next year.

'Think of this as a vegetable garden. We plant it this year, harvest it next year. So our next year's crop has been affected, and now the following year's crop gets affected.

'We are looking at two years down, so the devastation could be like the kiwifruit, it could be ongoing.”

Mortality rates this year are 30-80 per cent, in a normal year they are 5-10 per cent.

The virus identified as ostreid herpesvirus-1 (OsHV-1) has been found by MAF Biosecurity in oyster samples from affected farming areas.

'OsHV-1 cannot be transmitted to humans. Despite the name, there is no connection between OsHV-1 and herpes viruses in reptiles, birds and mammals including people,” says Ministry of Agriculture and Forestry response manager Dr Richard Norman.

OsHV-1 is not a World Organisation for Animal Health listed disease, meaning there are no trade issues.

It has been found in oysters in many countries including within Asia, North America, Europe and Australia where it has been associated with die-offs.

The virus is thought to have been in New Zealand for some time, with reports of its presence as early as 1992.

'At that time the molecular technology required to confidently confirm the virus, was not available,” says Richard.

MAF believes that the mortality is likely to be caused by a range of factors, triggered by unusually warm water temperatures. There has been no detection of any problem with oysters outside of the affected areas in the Eastern Bay of Plenty and Northland.

'The oyster industry is clearly facing significant production issues with a predicted shortfall for next year of approximately half of next year's harvest.

MAF will continue to work closely with the industry to identify other causes of the event and ways future production can be managed.”

The Pacific oyster industry is worth about $30 million each year.