Oyster disease detected near Stewart Island

By Karen Pasco

A Big Glory Bay wild oyster has tested positive for Bonamia osteae - the first time the fatal parasite has been found in a wild oyster bed in the Stewart Island area.

Biosecurity New Zealand director of response John Walsh said the find was not unexpected and did not increase the risk of the parasite spreading to infect other areas of 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 osteae."

However, with the sparse population of oysters in this area and it being a relatively enclosed body of water, there was a very low risk of any infection spread, he said.

The parasite infects flat oysters, such as New Zealand's Bluff oyster, causing the oysters to become ill and die. The parasite does not affect humans who consume the infected oysters.

A number of Bonamia infected oyster farms were removed from Big Glory Bay in 2017 after testing showed many were infected with the parasite.

Testing has continued in the wild oyster beds in the bay since that time.

A controlled area notice legally restricting the movement of shellfish between the areas of Stewart Island, Foveaux Strait and other wild oyster areas in New Zealand would remain in place.

"We remain committed to the programme to protect Bluff oysters through carrying on with this surveillance, both in Stewart Island and Foveaux Strait waters, as well as in other key ares including Marlborough Sounds, Tasman and the Chatam Islands," Mr Walsh said.