Single wild oyster infected with Bonamia ostraeae found in Big Glory Bay

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One wild oyster from Big Glory Bay in Stewart Island has tested positive for Bonamia ostreae through Biosecurity New Zealand’s surveillance programme.

Biosecurity New Zealand’s director of response, John Walsh, says the find is not unexpected and does not increase the risk of the parasite spreading to infect iconic Bluff oysters fished from Foveaux Strait.

“Even with the removal of oyster farms in 2017, we have been working under the assumption that Big Glory Bay would continue to contain low levels of Bonamia ostreae. It is a relatively enclosed body of water and wild oyster populations there are very sparse, so there is a very low risk of any infection spread,” Mr Walsh says.

The Bonamia ostraeae parasite infects flat oysters, such as New Zealand’s Bluff oyster, causing illness and death, and Biosecurity New Zealand has been working to keep the disease out of the Foveaux Strait fishery since it was first found in New Zealand in 2015.

Big Glory Bay is where a number of Bonamia-infected oyster farms were removed by Biosecurity New Zealand in 2017 in a bid to contain any spread of the parasite to the wild oyster fishery.

Since that time, Biosecurity New Zealand has carried out 7 rounds of testing on wild oysters from the bay and this is the first time the parasite has been found – a single oyster out of a sample of 150 in Big Glory Bay in this surveillance round.

“This shows our surveillance is effective, even at finding the disease when it is present at low levels,” says Mr Walsh.

“In total, with surveillance occurring in Stewart Island, Foveaux Strait, the Chatham Islands and Marlborough Sounds, we have tested over 8,000 oysters with only this single find since the 2017 detections in Big Glory Bay.

“We remain committed to the programme to protect Bluff oysters through carrying on this surveillance, both in Stewart Island and Foveaux Strait waters, as well as in other key areas including Marlborough Sounds, Tasman and the Chatham Islands.

“In addition, a Controlled Area Notice legally restricting the movement of shellfish between these areas remains in place.”

Biosecurity New Zealand’s next surveillance round will take place in February.”

A Technical Advisory Group is currently assessing the future of farming flat oysters in New Zealand, and the risk farmed oysters pose to uninfected wild oyster populations. Their report is due in November. This latest find will be considered as part of this review.

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