Puzzled scientists are battling to identify why millions of Pacific oysters are dying in New Zealand waters.
Up to half of the juvenile Pacific oyster stocks in the North Island are thought to have died, and up to 10 percent of the adults, according Oyster Industry Association chairman, Callum McCallum.
Aquaculture New Zealand said up to 80 percent of juvenile oysters on some farms have died.
The European Food Safety Authority (EFSA) has called on animal health experts for a scientific opinion on widespread die-offs of Pacific oysters (Crassostrea gigas).
Acting on a request from the European Commission, the EFSA has specifically asked whether the juvenile stocks may have been killed off by a combination of a herpes-like virus - Ostreid Herpesvirus-1 (OsHV-1) - and environmental factors.
In Britain, the movement of oysters from parts of the Kent coast has been banned after the herpes decimated juvenile Pacific oyster stocks.
The OsHV-1 virus has wiped out stocks in France in recent years, and Britain has declared a containment area on the Thames and north Kent coasts.
A spokeswoman for the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) said: "OsHV-1 is an emerging disease that has been associated with high levels of mortality in Pacific oysters in France, Jersey and some bays in the Republic of Ireland.
In 2008, France's main marine research institute, French Research Institute for Exploitation of the Sea (Ifremer), set up a crisis team which found 40 percent to 100 percent of oysters aged 12 to 18 months were dying from the oyster herpes.
Scientists found that an increase or a sudden change in the water temperature was an important risk factor, but the introduction of non-certified possibly-infected spat, movements and mixing of populations and age groups, among other husbandry practices, were key risk factors.
European authorities want increased biosecurity measures in their oyster aquaculture sector and tests on the health status of oyster spat before it is collected for farming.
Mr McCallum said restrictions had been placed on the movement of oysters into the few North Island bays where farms were not affected or to the South Island.
Until this year, around 3.5 million dozen Pacific oysters - around 2800 tonnes - were harvested annually in New Zealand's $30 million industry, with the majority exported, mainly to Australia and Asia, but about half of the oysters due to be exported next year are now dead.
"Stocks [for next year] are going to be reduced considerably,'' Mr McCallum said.
Aquatic disease specialists had taken approximately 250 samples for analysis, and Ministry of Agriculture and Forestry response manager Richard
Norman said speculating on the cause of the deaths would be premature.
