Bonamia ostreae

In May 2017, MPI detected the flat oyster parasite Bonamia ostreae on flat oyster farms in Stewart Island. Find out about the parasite, what we're doing to try to control its spread, and the rules that apply to the movement of shellfish and marine farm equipment.

What is Bonamia ostreae?

Bonamia ostreae is a parasite that can be fatal for flat oysters. Outbreaks of Bonamia ostreae overseas have severely impacted oyster fisheries, and it could have similar impacts here.

The parasite was first detected in New Zealand in the Marlborough Sounds in 2015, and subsequently discovered on flat oyster farms in Big Glory Bay, Stewart Island in May 2017.

Controlled Area Notice restricts shellfish movements

A Controlled Area Notice is in place to help prevent the further spread of Bonamia ostreae. This legally restricts movements of some shellfish species, including their spat, out of the Contained Zone (Nelson and Marlborough) and into the 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.

Controlled Area Notice [PDF, 4.5 MB]

You may need a permit

If you're moving restricted shellfish stock, or marine farm equipment and craft, into or out of zones covered by the Controlled Area Notice, you may need a permit.

Apply for a permit

What you can do to prevent the spread

If you’re out on the water, collecting shellfish or fishing in areas listed under the Controlled Area Notice, there are steps you can take to help prevent the spread of Bonamia ostreae.  

The risk of Bonamia ostreae spreading to flat oysters increases if any shellfish, or their discarded shells and waste, are moved from one area to another in the water. This risk is particularly high in Big Glory Bay and Paterson Inlet (Stewart Island).

To protect our wild oysters from Bonamia ostreae:

  • Don’t throw shells or shellfish waste overboard.
  • Return undersized or excess shellfish back to where you collected them.
  • Dispose of shells and shellfish waste at home or in a landfill.
  • Clean your fishing gear after you’ve finished collecting.
  • Keep your boat hull clean. 

How to spot infection

Generally, signs of the disease caused by Bonamia ostreae, which can often go undetected, are:

  • poor condition
  • gills that appear corroded
  • yellow discolouration of the gills and mantle.

Flat oyster farmers and harvesters who see these signs in oysters, or mass mortality, should call our Exotic Pest and Disease Hotline – 0800 80 99 66.

Fact sheet about Bonamia ostreae [PDF, 800 KB]

No food safety risk

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

What MPI is doing

Planning for long term management

MPI is planning for the long-term management of Bonamia ostreae and has identified key activities that aim to protect uninfected wild oyster populations. A Governance Group has been set up to support the delivery of a programme of work that:

  • maintains the Controlled Area Notice
  • provides for continued monitoring of wild oyster populations and marine farms

The programme also promotes biosecurity best practice and will identify when and where it may be appropriate for the farming of flat oysters to occur.

MPI’s response

MPI’s response to the incursion of Bonamia ostreae commenced in 2015, and was formally closed in December 2018. On 12 June 2017, following the detection of Bonamia ostreae in Stewart Island, MPI delivered a Notice of Direction to flat oyster farmers in Big Glory Bay in Stewart Island and Marlborough requiring the removal of all flat oyster stocks (examples provided below).  The removal of farms was completed in late 2017

Key documents produced during the response are provided below.

Compensation for losses

There are provisions for compensation under the Biosecurity Act 1993. If you can prove financial losses arising from MPI's exercise of powers under the Biosecurity Act, and your loss resulted from damage or destruction of property, or from restrictions placed on the movement or disposal of your goods – you can claim compensation for those losses.

Compensation is funded from a special appropriation from Parliament requiring, in some cases, Crown Law endorsement and Cabinet approval.

The Act gives clear grounds for compensation but the losses must have actually occurred and can be verified, and you have been unable to mitigate the losses by taking every step that is reasonable in the circumstances.

Affected parties have to apply for compensation. 

The amount paid depends on what verifiable losses have incurred as the result of any direction by MPI. Each situation will be different and every claim has to be assessed on a case-by-case basis. MPI's compensation team will assess claims under section 162A of the Biosecurity Act.

If you have questions about compensation email:

Welfare and support

The welfare of people affected by the response is important to us. We understand that many people may be worried about the activities and impacts associated with the Bonamia ostreae response. Stress and anxiety affect people differently – ask for help early.

Some groups that may be able to help include:

Help and information for fishers, oyster farmers and people affected by biosecurity responses' [PDF, 1.3 MB]


Who to contact

If you have questions about Bonamia ostreae:

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