As much as 50 per cent of the oysters that were to be harvested in 2011 have died. (Photo: Aquaculture New Zealand/FIS)

Unusual amount of Pacific oyster deaths investigated

The mysterious juvenile Pacific oyster deaths on aquaculture farms in the upper North Island are being jointly investigated by the New Zealand Oyster Industry Association for Aquaculture New Zealand (AQNZ) and the Ministry of Agriculture and Forestry’s (MAF) Biosecurity New Zealand.

Since the middle of last month, farmers have observed rising mortality rates of young oysters or spat on their farms from the Bay of Plenty in the east and from north of Kawhia in the west, commented AQNZ CEO Mike Burrell.

“Typically mortality rates for cultivated Pacific Oysters are between 5 and 10 per cent.  This year, however, the rates on some farms have varied between 30 to 80 per cent which is very concerning for the industry,” Burrell stated.

Callum McCallum, chairman of the NZ Oyster Industry Association, noted that about 80 per cent of the harbours in the North Island where oysters are farmed have suffered from excessive and unexplained deaths of the shellfish, which were to be harvested in late 2011, BusinessDay reports.

MAF’s aquatic disease specialists have gathered some 250 samples for analysis in an effort to learn the cause of the mortalities. 

The investigation is in its incipient stages, MAF Response Manager Dr Richard Norman told, such that to speculate on the cause of the deaths and any probably impacts would be a hasty move.

“What is clear is that both MAF and the industry understand the urgency around the issue and the need to identify the problem and find ways to address it,” Norman said.

Meanwhile, the New Zealand Food Safety Authority assured that no evidence suggests any food safety concerns in the country’s oysters either domestically or abroad.

Thus far, the primary effect the recently escalating mortalities is the possible dearth of juvenile oysters available for supplying oyster farms for next year’s harvests.

As much as 50 per cent of the oysters that were to be harvested in 2011 have died, as well as up to 10 per cent of mature oysters, McCallum informed.

"Stocks [for next year] are going to be reduced considerably. It's very bad. It seems that the smaller oysters are most affected,'' he said. 

Some 2,800 tonnes of Pacific farmed oysters are harvested each year in New Zealand, yielding revenue of around NZD 30 million a year. Most are exported to Australia and Asia.

No problems have been found with other varieties of oysters, including Bluff oysters.

Related article:

- Panel asked for advice on oyster deaths 

By Natalia Real
[email protected]
www.seafood.media

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