Bluff oyster parasite probe kept secret

A senior Ministry for Primary Industries investigator has spent the last six months trying to establish how a lethal parasite infected farmed Bluff oysters. David Williams reports.

An investigation into the outbreak of a deadly parasite in oysters farmed in a Stewart Island bay is complete. But the Ministry for Primary Industries (MPI) doesn’t intend to release the results publicly.

On May 31 last year, MPI said the parasite bonamia ostreae had been found in two oyster farms in Stewart Island’s Big Glory Bay. Less than a fortnight later, marine farmers were ordered to remove millions of oysters, in a bid to save wild oysters in Foveaux Strait, which were not infected.

MPI compliance investigation manager Gary Orr confirms in an emailed statement to Newsroom that its investigation is finished. Asked when the results would be made public, he says: “MPI does not publicly release information about investigations.

A senior MPI investigator worked full-time on the investigation for six months. Orr says compliance investigations vary in the time they take, depending on factors such as the number and availability of witnesses, the examination of document sand consultation with technical experts.

“This investigation is one of many that MPI undertakes.”

According to news reports at the time, Bonamia ostreae was first discovered in Big Glory Bay on May 24. In response, MPI restricted movements of shellfish, farm equipment and vessels in certain areas. The extraction of farmed oysters in the bay, so they could be loaded onto trucks and buried in a landfill, was completed on September 6.

‘Particularly destructive’

Bonamia ostreae poses no danger to humans. But Crown research institute NIWA describes it as “particularly destructive” within oyster fisheries, with a mortality rate of more than 90 percent in some cases. It’s already widespread in the northern hemisphere and has had a catastrophic effect in Europe. NIWA says it’s a waterborne disease and can spread through currents, other shellfish, as well as the movement of farm equipment and vessels.

The parasite was first found in New Zealand in early 2015, in the Marlborough Sounds and Nelson. Marlborough farmers were also required to remove their flat oysters last year.

That’s been a sore point for the Southland oyster industry. Bluff Oyster Management Company operations manager Graeme Wright blasted MPI’s response to bonamia as “incompetent” and “dysfunctional”. The day before MPI announced farmed oysters in Big Glory Bay would be removed, he told the Otago Daily Times had failed to act when international scientific advice was to remove infected oysters from the water in Marlborough.

“They’ve had two years to contemplate it ... but for whatever reason, MPI haven’t taken that action of removing those farms, and ‘bingo’ — it’s down here. They’re a group of specialists and they just seem to be dithering ... They’ve dropped the ball.”

Hundreds of thousands of dollars in compensation has already been paid in Southland. But most of that relates to the removal of farmed oysters and to help affected farmers switch to mussels. The latest round of tests for bonamia ostreae showed the Foveaux Strait fishery was clear of the parasite.

Bluff oysters were in hot demand when the season opened earlier this month, meaning supplies sent north of Invercargill were relatively scarce.

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