An investigation into the mysterious deaths of thousands of oysters in the North Island has found a herpes virus may be to blame.
The oyster industry has been experiencing significant losses of spat (juvenile oysters) in November and early December, with a mortality rate of up to 80% on some farms.
Ministry of Agriculture and Forestry response manager Richard Norman says it is believed the high spat death rate is probably due to a number of factors, triggered by unusually warm water temperatures.
However, Dr Norman says tests have identified the presence of ostreid herepvirus in oyster samples from affected farming areas.
He says the oyster herpes virus is throught to have been in New Zealand since the early 1990s. The technology needed to confirm the virus has not been available until now.
Dr Norman says the virus cannot be transmitted to humans and there is no food safety or human health risk associated with it.
However, he says the oyster industry is facing production issues with a predicted shortfall for next year of about half the normal harvest.
Big financial loss predicted
The Oyster Industry Association estimates the shellfish deaths could cost farmers at least $15 million.
Spokesperson Tom Hollings says it is likely farmers will look to breed the virus out of the population, but the deaths have already taken a financial toll.
The industry normally sells about $30 million worth of the shellfish every year and looks set to lose about half of that in 2011, on top of this year's losses, he says.