Return to oyster farming an 'unacceptable risk'

A scientific review has cautioned against future flat oyster farming in Stewart Island’s Big Glory Bay as an introduced parasite poses an "unnacceptable risk" to the wild oyster fishery.

Consultation will take place later this year on the future of flat oyster farming in New Zealand following the release of the review.

The review cautioned against future flat oyster farming in Big Glory Bay due to the threat Bonamia ostreae poses to the iconic wild Bluff oyster fishery in the adjacent Foveaux Strait.

The report, from a Technical Advisory Group (TAG) to those managing the Bonamia ostreae outbreak, says a return to farming in the bay would pose an unacceptable risk to wild (Bluff) oysters in Foveaux Strait.

Bonamia ostreae was first found in the upper South Island in 2015, then in Big Glory Bay oyster farms in 2017. Later that year, flat oyster farms in Big Glory Bay and in Marlborough were removed to protect wild fisheries from the parasite.

It is a parasite that can fatally infect flat oysters - overseas, outbreaks of Bonamia ostreae have severely affected wild oyster fisheries, and they could have similar effects here.

Biosecurity New Zealand’s director of response John Walsh said the TAG report was commissioned to provide a good scientific understanding of the risks presented by flat oyster farming and advice on the feasibility of farming in future.

"No decisions on the future of the flat oyster farming industry, particularly in Stewart Island waters, could be made without this assessment.”

A Governance Group comprising Biosecurity New Zealand, the fishing and aquaculture industries, Ngāi Tahu and local government agencies will ultimately provide recommendations to MPI on flat oyster farming, but Mr Walsh said no decision will be made without feedback from all affected parties.

"We’re planning a consultation process later in the year which will include meetings in both Stewart Island and Marlborough for iwi, wild catch fishers and aquaculture operators and anyone else with an interest. These meetings will be well publicised when dates and locations are set. There’ll also be ample opportunity for people to provide their views.”

The Technical Advisory Group report is available on MPI’s website, along with preliminary recommendations made by the Governance Group.

The report's conclusions included the level of disease risk posed by the development of flat oyster farming in New Zealand differs by location, but without protective measures, was high and unacceptable in some areas - given a positive detection of Bonamia ostreae during routine surveillance checks in October 2019 in Big Glory Bay, the TAG concluded that a return to flat oyster farming there posed an unacceptable risk to the wild oyster fishery in Foveaux Strait.

It also found a return to flat oyster farming should not occur without protective measures including further research, ongoing surveillance for the parasite and use of best biosecurity practice. This would include maintaining shellfish stock health and welfare, using pest and disease-free stock, following good cleaning and hygiene, checking farms for anything unusual, reporting abnormalities, and having a biosecurity management plan in place.

The report provided a process that can be followed to mitigate the risk posed by farming.

As part of the response to its discovery here, Biosecurity New Zealand put in place a Controlled Area Notice to protect wild oysters. This notice legally restricts movements of some shellfish species, including their spat, out of a Contained Zone (Nelson and Marlborough) and into a Protected Zone covering Southland, Otago and the Chatham Islands.

The notice also restricts the movement of some shellfish species, and marine farm equipment and craft, into and out of Stewart Island. These legal controls are still in place.

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