Bonamia ostreae parasite control in oysters
Bonamia ostreae is a parasite that infects flat oysters, including New Zealand's flat (Bluff or dredge) oysters (tio). Find out about Bonamia ostreae and what we're doing.
What is Bonamia ostreae?
Bonamia ostreae is a parasite that can kill flat oysters. Overseas it has significantly affected farmed flat oysters. However, we do not yet understand the effect it will have here, particularly on our species of wild oyster in our unique marine environment.
Bonamia ostreae was found for the first time in the Marlborough Sounds in 2015. In 2017, it was found in Big Glory Bay, Stewart Island. On 25 March 2021, Biosecurity New Zealand reported that it had been found in wild oysters from Foveaux Strait.
Bonamia testing process strengthened
In August 2021, a review found that an error had been made interpreting the March 2021 test results of oysters from Foveaux Strait. This led to results being reported as positive that should have been reported as inconclusive.
When the error was discovered, additional testing of the samples was carried out by the Australian Centre for Disease Preparedness and this was negative for the parasite. Biosecurity New Zealand is now confident there is no reliable evidence of Bonamia ostreae in Foveaux Strait oysters.
Corrective actions have been taken to ensure this cannot happen again. Improvements are also being made in the surveillance and testing programme for Bonamia ostreae which is contracted to NIWA.
Exclusion Zone Lifted
The legal controls and a rāhui that were put in place on fishing and vessel movements in the area in March 2021 are now lifted. This is following consultation with:
- mana tangata that hold mana moana over this area, and
- those involved in the oyster industry and community.
Controlled Area Notice
A Controlled Area Notice remains in place with controls on the movements of shellfish species, marine farm equipment and craft in other parts of the country.
Controlled Area Notice BRC 2021 [PDF, 523 KB]
The Controlled Area Notice restricts the movement of some shellfish species, and marine farm equipment and craft, into, through and out of Stewart Island. It also stops people 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.
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.
Who to contact for more information
If you have questions, or want to subscribe to updates on the Bonamia ostreae situation, email Bonamia2021.Liaison@mpi.govt.nz
No food safety risk from bonamia
Bluff oysters are safe to eat. Bonamia ostreae presents no food safety risk and has no human health impacts. Fresh, good quality New Zealand oysters continue to be safe to eat.
Bonamia ostreae is a different species to Bonamia exitiosa, which has previously affected the Bluff oyster fishery. The oyster fishing industry has worked through that particular situation to maintain a sustainable fishery.
How to spot Bonamia ostreae 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.
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. An MPI-led governance group is in place and includes representatives from:
- 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, and where necessary, review 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 demonstrated beyond doubt that the parasite is present in the bay and showed that the 2017 removal of flat oyster farms in Big Glory Bay to protect the nearby Foveaux Strait wild oyster fishery was appropriate.
At this time (October 2020), 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 late 2021.
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]
Surveys are carried out twice a year to test for Bonamia ostreae in oysters from around the South Island and Chatham Islands.
Bonamia ostreae investigation report [PDF, 4.2 MB]