Bluff oyster beds growing back despite killer disease

By Rebecca Fox

Initial results from a pre-season survey of bonamia in Bluff oyster fishery beds suggests the disease is still causing problems in some areas.

But despite this the fishery is continuing to rebuild, National Institute of Water and Atmospheric Research fisheries scientist Keith Michael says.

The commercial and recreational oyster fishing season starts today with the catch limit continuing at the industry's self-imposed level of 7.5 million, half of its 15 million annual catch entitlement.

Bonamia kills oysters by sapping their energy so they cannot keep their shells together, which exposes them to predators.

It is estimated to have killed about one billion Bluff oysters between 2000 and 2003. Since 2006, oyster mortality from bonamia has been relatively low.

Last month, Niwa and the Bluff Oyster Management Company surveyed the Foveaux Strait oyster beds for the disease.

Mr Michael said initial results and observations suggested the fishery was continuing to rebuild, especially in the core commercial fishery areas in central Foveaux Strait.

"Oyster densities have increased at most sites, with some sites more than doubling from last year."

But bonamia was still causing problems in other areas.

Oyster samples were being examined at Niwa's Greta Point laboratory, and the investigation was due to be completed this month, he said.

Barnes Oysters manager Graeme Wright said last year's survey had shown low levels of bonamia.

"We're eager to see what this survey will show and what we'll see when we're at sea."

Once the industry had data from the survey and from time out fishing, it would assess whether the quota needed to be adjusted.

"It's steady as we go. In three or four weeks we'll have a fairly good idea of what's happening."

Ministry of Fisheries inshore fisheries officer Allen Frazer said bonamia was most active during summer and autumn and appeared to be influenced by environmental conditions such as sea temperature.

There had been concerns higher water temperatures in summer might have had an effect on bonamia levels.

The results would help to predict how many oysters bonamia was likely to kill over the coming season.

The long-range forecast for today suggested a change to northwest winds of 46km/h with a moderate southwest swell.

Mr Wright said pre-season demand for oysters was normal with the delicacy expected to be available from tomorrow morning if the fleet of 11 boats went out.

The price was still to be set, but Mr Wright hoped to keep it consistent with last year at $20 a dozen.

The season ends on August 31.

- OTAGO DAILY TIMES

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