An incurable herpes-like virus is behind the widespread deaths of juvenile Pacific oysters in upper North Island marine farms, Ministry of Agriculture and Forestry (MAF) has confirmed.
That is going to have a huge financial impact, with farmers bracing for a huge drop in crop numbers and an impact on their sales next year.
The $30 million oyster farming industry disclosed last week that it had been experiencing big losses of juvenile oysters over November and early December.
Half the aquaculture industry's farmed oysters due for harvest in 2011 had died on at least 11 oyster farms from Parengarenga Harbour in Northland to Ohiwa in the eastern Bay of Plenty.
On some farms, up to 80% of juvenile oysters had died, compared with 5% to 10% in a normal year.
MAF believes the virus had been present in New Zealand since the early 90s, triggered off by environmental factors.
Marine pathologists at MAF used molecular tests and DNA sequencing to show the presence of ostreid herpesvirus-1 (OsHV-1) in samples from affected oyster farms, and MAF response manager Richard Norman said it was possible the die-off had been due to a range of factors, triggered by unusually warm water temperatures.
"Elevated water temperatures may be potentiating or kicking off the effect in the small oysters that are affected," he said.
Ostreid herpes viruses are known to affect not only oysters but also clams, scallops, and other molluscs, according to French Research Institute for Exploitation of the Sea pathology lab director Tristan Renault.
He has suggested in Europe that global warming could be an explanation of the appearance of this particular type of the virus.
Oyster herpes virus is specific to shellfish and is not unrelated to the herpes viruses that affect humans and other animals, though the oyster virus cannot be transmitted to humans.
The Food Safety Authority has also confirmed there is no food safety risk to consumers.
A strain of the virus killed between 20 to 100% of breeding Pacific oysters in some French beds in 2008, 2009, and 2010. That virus has since has spread into British waters.
There is no way of treating the herpes virus and farmers can only hope oysters will eventually breed resistance to it.
"The ones that live through it must have some sort of gene that's missing in the others, so we're looking at a reasonably short to medium term that the oysters will breed their way through this," oyster farmer Callum McCallum told ONE News today.
And the virus is not likely to stop oyster exports either.
"It's all around the world, so all of our trading partners, Australia, America, Europe and Asia, have had it at some stage," McCallum said.
But it is expected that the virus will have a "significant" financial impact on New Zealand's oyster industry, which will trickle down to consumers.
"As of next year there'll be definite price movements, just relating to the amount of oysters we've got to sell, compared to what we've done [in the past], so that's sad, but that's just life and these things happen," McCallum said.