health & science

Scientist muzzled over oyster parasite

A government ministry puts a scientist off-limits after the re-discovery of an oyster parasite. David Williams reports.

It was portrayed as the possible end to Bluff oysters. After the 2017 bombshell find of an oyster-killing parasite, the threat to the Foveaux Strait fishery led to the removal of all oyster farms in Stewart Island and Marlborough.

That decision was based on science. But confirmation this month that the parasite, Bonamia ostreae, still exists in Stewart Island’s Big Glory Bay won’t be explained by a scientist.

Newsroom asked to speak to Keith Michael, a fisheries scientist who leads the B. ostreae sampling and testing project for National Institute of Water and Atmospheric Research, NIWA, under contract to the Ministry for Primary Industries. MPI refused the request. We were referred to its Biosecurity New Zealand unit, which issued an emailed statement from response director John Walsh.

In it, Walsh says: “As it’s the ministry’s programme and we own the data, it’s appropriate that all enquiries about the programme are directed to us.”

But there’s research suggesting that statements made by institutions – particularly university press offices – can lead to misleading or hyped claims about science in news stories.

University of Auckland Professor of Physics Shaun Hendy, the author of Silencing Science, says testing the strengths and weaknesses of science requires direct access to experts. With filtered conversations, particularly those passed back and forth via email, the message can be “potentially massaged”.

“Publicly-funded science should be available to the public,” Hendy says. “Journalists ought to be able to talk to the experts rather than having messages filtered through institutions and other organisations.”

The 2017 operation to remove oyster farms has resulted in compensation of more than $5.4 million being paid to eight different marine farmers. It has also sowed the seeds of distrust, especially among those whose livelihoods have been destroyed.

Bubble bursts on world first

B. ostreae is a tiny parasite that can be deadly for flat oysters but harmless to humans. It enters the gills, mantle, and gut of the oyster, and then multiplies rapidly in blood cells. While mildly infected oysters appear healthy, others can experience yellowing of their soft tissues, and surface lesions of the gills and mantle. Intense infections kill the oyster.

The parasite devastated flat oyster production in parts of Europe, particularly France.

(Infection rates of farmed oysters in Marlborough’s Queen Charlotte Sound were up to 100 percent, according to 2016 research led by NIWA’s Michael.)

After two years of clear tests, the Ministry of Fisheries stuck its neck out in July, suggesting that if testing remained clear, Big Glory Bay would be the first example of bonamia eradication in the world.

Why wouldn’t it? Soon after the outbreak, NIWA’s Michael said that it’s a waterborne disease, spread by infected cells being released by dying oysters. Also, B. ostreae cells persist in seawater for only a few days, while most of the bay’s water stays for seven to 13 days.

Removing the farms removed its highest chance of persisting and progressing.

The latest find, then – a single wild oyster from Big Glory Bay testing positive for B. ostreae ,announced two Fridays ago – might be seen as a huge blow.

But it was brushed aside by Biosecurity NZ as “not unexpected” and a sign its surveillance is effective. It wasn’t sufficiently exercised to increase surveillance. The risk of infection spreading to Foveaux Strait didn’t increase, Walsh said in a statement, mainly because of the bay being “relatively enclosed” and having “sparse” wild oyster populations.

Comfortable, not happy

Graeme Wright is the operations manager for Bluff Oyster Management Company, which runs the fishery on behalf of the 16 Foveaux quota owners. He’s also the manager of Barnes Oysters, which processes about 60 percent of the quota through its factory.

The positive B. ostreae test is “a little bit troubling”, Wright says, but he parrots Walsh’s line about it not being totally unexpected. “I guess it means the system works.

“It is the sea – you can’t eradicate all oysters. Science tells us conclusively the risk is around the densities of oysters and we know the ministry’s done a fantastic job of de-stocking the area.”

Fiona MacMillan, Sanford’s corporate communications general manager, says the recent discovery has no impact on its operations in Big Glory Bay. “Like everyone else, we have no oyster farming left in the area. We farm mussels and salmon, neither of which is impacted.

“We put all the required extra biosecurity measures in place when the first positive Bonamia ostreae findings were reported back in 2017 and we have never stopped using those additional measures.”

Since news broke on October 11, Wright has been speaking with Biosecurity NZ about what the parasite’s persistence means for commercial operators. Is the industry happy that more testing isn’t scheduled until February? “We’re comfortable with it, I wouldn’t say happy with it.”

Wright says MPI has had good science advice, including from panels with international experts. And science is expensive, he says, which means his industry has to be realistic.

“We’d like to test for it every week if we could, but you’ve got to be practical.”

He’s also reassured by advice from the industry’s own science advisers – NIWA, the same institution employed to do sampling and testing for B. ostreae. At least the advice is likely to be consistent.

Spat over size, age

Bluff’s Rodney Clark is a former oyster farmer, whose company has been ruined by the removal of its farm in Big Glory Bay. The former paua diver spent 14 years examining Bluff oysters, developing a variety that was tolerant of Bonamia exitiosa – the endemic close relation of B. ostreae.

In June 2017, as the removal of farms was being considered, Clark says he warned officials that if they were serious about stopping the spread of B. ostreae into Foveaux Strait they’d need to remove all shellfish from the bay. That’s because the most likely place for baby oysters (spat) to settle is on shells – of any type.

Mussel lines with oysters on them were pulled but MPI decided to leave the lucrative mussel-only farms alone. Clark: “I also told them they had one chance to do this task properly, because if they didn’t it was to be a far bigger job and way more expensive than doing it properly the first time.”

Academics are listened to, Clark laments, while unqualified people like himself – those who get their hands dirty and understand the practicalities – are disregarded.

Biosecurity NZ’s Walsh says the recently-discovered infected oyster was number 41 from a batch of 50 taken from an area near the former oyster spat farm run by Tio, the joint venture partner of Seafood giant Sanford. The infected individual was 29mm long and 38mm high, so it was relatively small.

Oysters can’t be aged, Walsh says, so it’s hard to infer anything. “It is the intensity of infection found that is more important than the size of the oyster.”

Clark insists the size is concerning. It’s too small to have come from the spat from an infected farm in 2017, he says, which suggests it’s a “third generation” infected oyster. “If I’m correct, there is a generation of infected oysters MPI and NIWA have not found.”

Biosecurity NZ’s Walsh says oysters die when the infection intensifies. “It is not generational.” He says it’s inconclusive that B. ostreae passes from a parent oyster to larvae, but that it’s more likely transmitted between oysters through water. (A French study in 2011 concluded transmission of the parasite from adult to larvae is possible.)

A map (with water counterintuitively in white) of Bonamia ostreae sampling sites. BGB_3, in the yellow box, is where the 2019 infected oyster was found. Image: MPI

However it was transmitted, the facts are that the parasite is present more than two years after it was first detected.

But there’s no rush from officials to find other infected oysters.

Wild oysters are in such low densities in Big Glory Bay, Walsh says, that it may not be possible to find enough oysters in some places to get accurate tests.

Another protective measure is that movements of marine farming craft and equipment in and out of Stewart Island are subject to controls and permitting. (Although, similar controls in Marlborough didn’t prevent B. ostreae from moving 900 kilometres south to Stewart Island – and no one was held accountable.)

When the next survey’s done in February, they will sample the same seven sites – three in Big Glory Bay, three in Patterson Inlet, and one in Bluff Harbour. (Biosecurity NZ’s sampling programme follows protocols recommended by the World Organisation for Animal Health, including the frequency of six-monthly intervals, which allows time for infection to develop.)

Those sites were determined by a 2017 survey mapping the distribution of oysters. Almost all wild oysters in Big Glory Bay are found between the low water tide mark and a depth of two metres, Walsh says. “That is why there is not sampling in the middle of Big Glory Bay and Paterson Inlet – there are virtually no oysters there.”

But wouldn’t the dynamics of wild oysters have changed since 2017, perhaps because of spat from the now-removed farms?

Larvae are typically released and settle between November and February, Walsh says. The farms were removed in July and August, and the area was surveyed in September. “There are not likely to have been brood stocks present to produce large numbers of larvae.”

However, Clark has been told that mussels harvested last season in Big Glory Bay were covered in oysters, some large enough to be breeding age. He worries these oysters might have been breeding and spreading B. ostreae.

Confirmation of an infected oyster means Big Glory is likely to be a ticking time bomb for the wild fishery in Foveaux Strait, Clark believes. “If I’m correct, they’ll get more of this and it’ll only get worse from now on,” he says. “This will move, and they’ll continue to find it.”

Nerves over supposed silver bullet

Aquaculture is still being held up as some sort of economic silver bullet for Southland.

In 2017, after the oyster farms were removed, a Southland development strategy called aquaculture the region’s “single biggest opportunity”.

Last year, the Government pledged $425,000 from its provincial growth fund to pay for a business case for a commercial salmon and mussel hatchery in Southland. Earlier this month, Finance Minister Grant Robertson said Southland could play a key role in the country’s push to be a world leader in sustainable and innovative aquaculture.

Prime Minister Jacinda Ardern touched on this theme during a speech at the United Nations in New York last month, when she declared New Zealand was “determined to show that we can be the most sustainable food producers in the world”.

Wright, of Barnes Oysters, reckons aquaculture will be a big part of that plan. “It makes sense at all sorts of levels.” But he’s still nervous.

Next month, a technical advisory group to Biosecurity NZ will report on the future of farming flat oysters. Considering what the industry has been through over the last couple of years, Wright says authorities have to be careful to ensure aquaculture and wild fisheries co-exist safely.

Of the advisory group report, he says: “We’ll certainly be watching that with bated breath.”

One wonders what the scientists on the advisory group will say – and if they’ll be available for an interview.

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