Aotearoa Fisheries has given up on breeding Pacific oysters in Northland and Coromandel because of a virus.
Oyster herpes has been devastating the Pacific oyster industry since 2010 when it killed 95% of young oysters raised from wild spat.
Aotearoa Fisheries says its new strategy is to raise the oysters from cultured spat at Nelson's Cawthron Institute then truck them back up north to fatten them in winter when the virus is less active.
General manager Don Collier said it is an expensive option, but there's little choice.
An aquaculture scientist says increased ocean acidity may be a factor in the disease.
Nick King, of the Cawthron Institute, said the virus has probably been around as long as the oysters have, but a recent variation is killing the shellfish in New Zealand and overseas.
He said that could be related to environmental factors such as warmer summers, more sediment, and a change in the PH value of the sea as it absorbs more carbon dioxide.
The institute is working on a programme to breed a Pacific oyster that is immune to the virus.