Three wild oysters were found to be infected with Bonamia ostreae in a small area in the Foveaux Strait, near Stewart Island.
As such, Biosecurity New Zealand will begin further testing of the oysters, although no infection was found in the other five sample sites.
Bluff oyster quota holders, who are in the middle of this year’s oyster season, will be able to continue to fish, and Biosecurity New Zealand will work with them on the best course of action.
This was likely to be a small temporary and voluntary ‘no take’ zone around the area where the oysters were found until longer term options were explored.
The parasite was first found in New Zealand in 2015 in oysters from the Marlborough Sounds and then in 2017 in oysters in Big Glory Bay in Stewart Island.
Consequently, an extensive programme was funded to protect wild populations which included removing a number of flat oyster farms in Big Glory Bay, and running a surveillance programme to look for early signs of the parasite in the wild.
Biosecurity Manager Dr Cath Duthie said it was, however, always considered possible that a find in wild oysters could occur.
"Foveaux Strait is a dynamic waterway with strong currents and the parasite can remain dormant.
“For this reason, we commissioned Niwa to do six-monthly surveillance sampling and testing of wild oysters from six different locations in the Strait to find any infections at the earliest possible time. We received a confirmed positive laboratory result for Bonamia ostreae from the three oysters today. "
She said commercial Bluff oyster fishers had not reported any sign of the disease and it was not detected in five years of six-monthly surveillance sampling in the area.
No commercial oyster fishing vessels have been working the affected area so far this season.
“The fishery has been affected for many years by a different type of Bonamia – Bonamia exitiosa.
"The oyster fishing industry has worked through that situation to maintain a sustainable fishery. We’ll work to support them to explore ways through this new challenge.”
In the coming weeks, Biosecurity New Zealand will work closely with the Bluff oyster fishers, iwi, other marine users and the wider public on the most appropriate and effective response to the situation.
“We’ve talked to fishing industry partners today and will be in Southland tomorrow to start talking to the local community. We want to involve local people, including the iwi of the area, in our response.
“Our immediate focus is to carry out more testing in Foveaux Strait to understand if and where else the parasite is, to enable the best future decisions."
Bonamia ostreae is not a food safety issue and fresh good quality Bluff oysters remain safe to eat.
It can be hard to spot the disease caused by the parasite but common symptoms in oysters include poor condition, gills that look corroded, yellow discolouration of the gills and mantle.
Seven oysters from a routine surveillance sample of 50 collected from Big Glory Bay on Stewart Island tested positive for infection with Bonamia ostreae in late October last year.
However, the MPI website states it was not believed that discovery would increase the risk of the parasite spreading to the Bluff oyster fishery.
"Big Glory Bay is a relatively enclosed body of water and wild oyster populations there are sparse, so the risk of any spread remains low."
It said it demonstrated beyond doubt that the parasite was present in the bay and shows that the 2017 removal of flat oyster farms in Big Glory Bay to protect the nearby Foveaux Strait wild oyster fishery was appropriate.
