MPI detects oyster parasite on Stewart Island

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The Ministry for Primary Industries (MPI) has today confirmed the detection of Bonamia ostreae in 2 oyster farms on Stewart Island.

Bonamia ostreae is a parasite that can be fatal for flat oysters. It has been in New Zealand since at least 2015 in the Marlborough Sounds and Nelson, but this is the first time it has been found in another area of New Zealand.

There is no food safety issue from eating oysters with Bonamia ostreae. Fresh, good quality New Zealand oysters continue to be safe to eat.

"Bonamia Ostreae is a naturally occurring parasite and is difficult to contain and eradicate as it spreads easily through ocean currents and on vessels," says MPI Biosecurity Surveillance and Incursion Manager Brendan Gould.

"This particular strain of Bonamia has been in New Zealand since at least 2015, however strains have been here since the 1960's and are present in the marine environment."

MPI's priority is determining the extent of the issue and limiting further spread.

Extensive sampling to date has not found Bonamia ostreae in Bluff oysters in Foveaux Strait.

MPI has reissued a Controlled Area Notice legally restricting movements of some shellfish species, including their spat, into and out of Nelson, Marlborough Sounds and Stewart Island. It also legally restricts movements of farm equipment and vessels out of Stewart Island to limit further spread.

"We are concerned that Bonamia ostreae has been found in Stewart Island, and our priority is on determining the extent of the problem and limiting further spread," says Mr Gould.

"The new detection on Stewart Island was made as part of an MPI surveillance programme for Bonamia ostreae. Extensive sampling to date has not found Bonamia ostreae in Bluff oysters in Foveaux Strait, however, we are continuing our sampling and have increased our surveillance."

Internationally, Bonamia ostreae has had an impact on flat oyster stocks, and it has also impacted farmed flat oyster stocks in Marlborough and Nelson since it was detected in 2015.

Seafood species such as Greenshell mussels and Pacific (rock) oysters are not affected by Bonamia ostreae, however, they may carry and transmit it to flat oysters.

Mr Gould says that Bonamia ostreae is an infectious organism and because it is in the marine environment, there are number of complexities and variables that must be considered in managing spread.

"Because Bonamia ostreae is in the marine environment, it makes it particularly tricky to control, as water currents and other factors can affect spread. It is also difficult to detect in the environment and it is unclear how Bonamia ostreae made it to Stewart Island."

"We're committed to doing everything we can to limit the spread of Bonamia ostreae to other areas," says Mr Gould.

"While it's still early days, I would like to acknowledge and thank the flat oyster farming operators on Stewart Island and others in the industry for their cooperation and help in responding to this latest Bonamia ostreae find."

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