Oyster parasite found on Stewart Island

Two oyster farms on Stewart Island have Bonamia ostreae, a naturally occurring parasite. The Ministry for Primary Industries (MPI) confirmed the detection, saying the parasite can be fatal for flat oysters; however, there is no food safety issue from eating oysters with the organism.

Fresh, good-quality New Zealand oysters continue to be safe to eat. Bonamia ostreae has been in the Marlborough Sounds and Nelson, New Zealand since 2015, but this is the first occurence in another area of New Zealand.

MPI’s priority is determining the extent of the issue and limiting further spread. It 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, along with movements of farm equipment and vessels.

“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,” said MPI Biosecurity Surveillance and Incursion Manager Brendan Gould.

“The new detection on Stewart Island was made as part of an MPI surveillance program 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. 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.

Gould added 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,” he concluded.