MAF scientists have identified a strain of the herpes virus as the cause of a swathe of unexplained deaths on North Island’s oyster farms.

Farmers began reporting the deaths in late November, and tests have found the herpes virus – which can’t be passed on to humans – as the likely cause.

The virus is thought to have been here as early as 1992, but conditions this season have finally let it flourish.

Tom Hollings of the Oyster Industry Association says the sector will incur significant losses as a result.

There’s an oyster virus, it seems to be a necessary part of the excessive mortality environmental conditions come into play as well.

"The mortality is about the same as it was last week, it hasn’t been much more. We’ve lost about half of next year’s crop through this juvenile mortality."

Tom Hollings says extra losses – including jobs – are also likely in the short term.

"We usually have sales income of $30m a year. We may be looking half of that this year. There’s issues for individual farmers in terms of their financial position, there’s issues for employment."

The virus isn’t expected to affect our oyster exports.

The disease has been found in many other oyster-producing countries in Asia, North America and Europe.