Bonamia ostreae parasite control

Bonamia ostreae is a parasite that infects flat oysters. It is a serious concern for New Zealand flat (Bluff or dredge) oysters, including the Bluff fishery. Find out about Bonamia ostreae, what we're doing to try to control its spread, and associated rules on moving shellfish and marine farm equipment.

What is Bonamia ostreae?

Bonamia ostreae is a parasite that can kill flat oysters. Outbreaks have severely damaged overseas oyster fisheries, and it could have similar effects here.

Bonamia ostreae was detected for the first time in the Marlborough Sounds in 2015. In 2017, it was found in Big Glory Bay, Stewart Island. All flat oyster farms in these areas were removed to prevent the spread of the parasite.

Bonamia ostreae is a different species to Bonamia exitiosa, which has previously affected the Bluff oyster fishery.

How to spot infection

It can be hard to spot the disease caused by Bonamia ostreae. Common symptoms in oysters are:

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

Bonamia ostreae can also cause widespread oyster deaths.

Flat oyster farmers, harvesters, and fishers should keep an eye out for these signs. If you see anything suspicious, 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

Controlled area notice restricting shellfish movements

A controlled area notice was put in in place by MPI to stop the spread of Bonamia ostreae and protect oyster fisheries. This notice legally stops people from moving some shellfish species out of a designated contained zone (Nelson and Marlborough) and into a protected zone (Southland, Otago, and the Chatham Islands). It covers all life stages of these species, including their spat.

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 including map of zones [PDF, 4.5 MB]

You may need a permit

You may need a permit to move restricted shellfish stock, or marine farm equipment and craft, into or out of zones covered by the controlled area notice.

Apply for a permit

What you can do to prevent the spread

There are steps you can take to help prevent the spread of Bonamia ostreae. These are important if you're out on the water, collecting shellfish, or fishing in areas covered by the controlled area notice.

The risk of spread increases if any shellfish, or their shells and waste, are moved from one area to another.

To protect our wild oysters from Bonamia ostreae:

  • keep your boat's hull clean
  • dispose of shells and shellfish waste at home or in a landfill – don't throw them overboard
  • return undersized or excess shellfish back to where you collected them
  • clean your fishing gear after you've finished collecting.

Long term management of Bonamia ostreae

MPI is leading the long-term management of Bonamia ostreae in New Zealand.

The biosecurity response was closed in December 2018. An MPI-led governance group has now been set up. It includes:

  • Biosecurity New Zealand
  • Aquaculture New Zealand
  • Fisheries New Zealand
  • Environment Southland
  • Awarua Runaka
  • Southland District Council
  • the Bluff wild oyster fishery.

The governance group will support a programme to:

  • maintain the controlled area notice
  • monitor wild oyster populations and marine farms
  • find out if oyster farming can start again.

The programme includes twice yearly surveillance to check for the spread of Bonamia ostreae. The programme also promotes biosecurity best practice.

Detection in 2020 of bonamia infection in wild oysters from Big Glory Bay

Seven oysters from a routine surveillance sample of 50 collected from Big Glory Bay on Stewart Island tested positive for infection with Bonamia ostreae in late October 2020.

This detection demonstrates beyond doubt that the parasite is present in the bay and shows that the 2017 removal of flat oyster farms in Big Glory Bay to protect the nearby Foveaux Strait wild oyster fishery was appropriate.

It is not believed this October 2020 discovery will increase the risk of the parasite spreading to the Bluff oyster fishery. Big Glory Bay is a relatively enclosed body of water and wild oyster populations there are sparse, so the risk of any spread remains low.

No bonamia was found in other surveillance samples taken from Horseshoe Bay in Stewart Island, Paterson Inlet, Foveaux Strait, Bluff Harbour, Cloudy Bay, Tasman Bay, and the Chatham Islands.

Future of farming – Technical Advisory Group report

A Technical Advisory Group (TAG) was formed in September 2019. The TAG looked at whether flat oyster farming poses a risk to wild oyster populations and the Bluff oyster fishery. A report was written to give the Bonamia governance group the information they need to recommend if, where, and when flat oyster farming might start again.

Future of farming – Technical Advisory Group report [PDF, 1.3 MB]

When the governance group received the TAG report they made some preliminary recommendations.

Preliminary recommendations [PDF, 444 KB]

No decisions will be made on the future of flat oyster farming without feedback from those it affects.

Consultation is being planned for 2021. This will include public meetings in Stewart Island and Marlborough. These meetings will be well publicised once dates and locations are decided.

MPI will publish a discussion document, and written feedback will also be encouraged. All feedback will go to the governance group whose members will consider stakeholder feedback and the Technical Advisory Group's report, and make recommendations to MPI.

Iwi and affected stakeholders will be notified once any decision has been made.

Media release 23 July 2020:  Consultation planned on future of flat oyster farming

MPI's initial biosecurity response to Bonamia ostreae

MPI's response to Bonamia ostreae started in 2015 when the parasite was found in oysters from the Marlborough Sounds. In early 2017, Bonamia ostreae was also found in Stewart Island.

On 12 June 2017, MPI delivered a notice of direction to flat oyster farmers in Big Glory Bay in Stewart Island and Marlborough. This notice required the removal of all flat oyster stocks. All farms had been removed by late 2017.

Notice of Direction Big Glory Bay [PDF, 484 KB]

Notice of Direction Marlborough [PDF, 464 KB]

Fact sheet about Bonamia ostreae response [PDF, 297 KB]

Twice yearly surveys are carried out to test for Bonamia ostreae in oysters from around the South Island and Chatham Islands.

Bonamia ostreae investigation report [PDF, 4.2 MB]

Report of the Technical Advisory Group on resilience breeding in flat oysters [PDF, 616 KB]

Who to contact

If you have questions about Bonamia ostreae:

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