Bonamia ostreae: New controls to prevent spread of oyster disease

Bonamia ostreae is not a food safety risk and fresh, good-quality Bluff oysters are safe to eat. Photo / Jason Oxenham

New rules to protect flat oysters from the disease-causing parasite Bonamia ostreae now apply to recreational fishers and boaties in some New Zealand waters.

Bonamia ostreae is in the Marlborough Sounds and Big Glory Bay at Rakiura, Stewart Island.

It infects and eventually kills flat oysters (commonly known as Bluff oysters or tio). It is, however, not a food safety risk and fresh, good-quality Bluff oysters are safe to eat.

Biosecurity New Zealand deputy director-general Stuart Anderson said a new Controlled Area Notice (CAN) came into force on September 1.

The notice placed conditions on the movements of vessels and shellfish in the upper South Island, Big Glory Bay, the Chatham Islands and the lower South Island, Anderson said.

“This new CAN replaces existing legal controls on commercial operators in these areas.”

The rules now applied to recreational fishers and boaties as well. “In addition, the boundaries of some controlled areas have changed, and we encourage all boaties, fishers and vessel operators to be aware of these rules.”

Anderson said the controls were there to protect New Zealand’s “iconic” Bluff oyster, which was highly valued, both commercially and culturally.

Under the CAN, areas where Bonamia ostreae is known to be present are designated as contained zones. Areas that are free of the disease and which are known to have significant populations of flat oysters are protected zones.

The rules cover the movement of shellfish into and out of these zones, and the fouling of boats and gear (visible sea life including shellfish, algae or weed) in these zones.

The contained zones are in the upper South Island and Big Glory Bay in Rakiura / Stewart Island. The protected zones are the lower South Island and Chatham Islands.

The rules:

• Flat oysters must not be moved into or out of the Big Glory Bay contained zone.
• All shellfish or shellfish waste (including shells) collected in a contained zone cannot be put in the sea outside the zone.
• Vessels and gear must not be moved into or out of a contained zone unless they are visibly clear of fouling unless a permit is obtained.
• Shellfish or shellfish waste from outside a protected zone must not be put in the sea inside the protected zone.
• Gear must not be moved into protected zones unless it is visibly free of fouling.

Anderson said clubs, marinas, charter operators and businesses in affected areas had been spoken to as part of raising awareness of the revised rules and what they needed to do to prevent the spread of Bonamia ostreae.

Biosecurity NZ had put up signs at boat ramps, ferry terminals, wharves and huts to tell people about the new rules and this was being reinforced with an advertising and social media campaign, he said.

“If you boat or fish anywhere in New Zealand, it’s really important to keep your hull and gear clean. Remove any plant material or shellfish as it can spread the Bonamia ostreae parasite and other marine pests.”

A slight layer of slime and barnacles was OK, but nothing else, Anderson said.

“Pull weeds off any fishing, diving or other gear that you take out of the water and put it back in the sea where it came from before you move on.

“If you find something on your gear later, in a new location, do not put it in the sea.

“Place it in a plastic bag and put it in the rubbish back on land. You should also do the same with shells and other waste after eating shellfish.”

Diseased shellfish might look healthy but even their empty shells could spread the parasite, Anderson said.

Details of the rules, including conditions that apply to marine farm operators and information on applying for special permits, can be found on MPI’s website.