Bonamia still about, but oysters bounce back

Initial results from a pre-season survey of bonamia in Bluff oyster beds suggest the disease is still causing problems in some areas, but despite this the fishery is continuing to rebuild, a scientist says.

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

Bonamia, a disease that kills oysters by sapping their energy so they cannot keep their shells together, which exposes them to predators, 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, the National Institute of Water and Atmospheric Research (Niwa) and the Bluff Oyster Management Company surveyed the Foveaux Strait oyster beds.

Niwa scientist Keith Michael said initial observations suggested the fishery was continuing to rebuild, especially in the core commercial areas in central Foveaux Strait.

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

However, bonamia was still causing problems in other areas, with oyster densities decreasing, he said.

Oyster samples were being examined at Niwa's Greta Point, Wellington, laboratory.

The investigation was due to be completed in early March, he said.

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

"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 or not 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 earlier in summer might have had an impact on bonamia levels but that would not be known until the results were through, he said.

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

The marine forecast for today is for 20 knot easterlies tending northerly, before a change tonight to 30 knot westerlies and rough seas.

Mr Wright said oysters should be available from tomorrow morning if the fleet of 11 boats was able to go to sea today.

"Everyone wants the first of them."

It was hoped that demand would help raise funds for Invercargill's Relay for Life.

A sack of oysters would be helicoptered off a boat on Monday and flown to Invercargill to be auctioned and sold on the streets.

While the price was still to be set, Mr Wright hoped to be able to keep it consistent with last year's, which was $20 a dozen.

He said pre-season interest in oysters was on a par with previous years.

The season ends on August 31.

rebecca.fox@odt.co.nz