Authorities have not ruled out the possibility a devastating virus could slip through quarantine measures in New South Wales and obliterate the nation’s multi-million dollar oyster industry.
Tests this week confirmed Pacific Oyster Mortality Syndrome (POMS) had reached a major tributary of the Hawkesbury River, between Sydney and Newcastle.
It was also detected in the Georges River and Port Jackson in 2010 and 2011.
The latest outbreak has inflicted a devastating blow on fourth-generation oyster farmer Rob Moxham, destroying about 90 per cent of oysters across 50 hectares.
With no resistance to the virus, oysters that had been healthy on Monday were felled - in their millions - virtually overnight.
This morning, the NSW Department of Primary Industries confirmed the virus had spread to another part of the river.
The development has sent shock waves through the nation’s seafood industry, particularly other Pacific oyster growing areas in NSW, Tasmania and South Australia.
Tasmania’s oyster industry – which directly employs more than 300 people – is largely based around Pacific oyster production. The oyster industry is the second largest aquaculture sector in South Australia.
Oysters Tasmania executive officer Dr Tom Lewis said the chances the virus would spread to that state were remote given bio-security measures and the island’s isolation from the mainland. But the organisation was preparing an ‘action plan’ should it happen, he said.
“The move of the virus from Botany Bay up to the Hawkesbury was something that almost couldn’t be stopped,” Dr Lewis said. “It was merely a matter of when, not if unfortunately.”
When asked if it was inevitable that the disease would spread to other parts of NSW and interstate, aquaculture manager Ian Lyall from NSW Department of Primary Industries described it as the “million-dollar question”.
“All of the estuaries are on heightened alert to watch for any unexplained mortalities and clearly, the other states have a watching brief and are considering this issue,” he said.
He said the task of containing the virus was complicated by a lack of understanding about how it spread.
“There’s just so much unknown about the movement of the virus,” Mr Lyall said.
The Hawkesbury produces more than 300,000 dozen oysters a year, about half the state's Pacific oysters, worth an estimated $2.4 million.
About 20 per cent of the local industry's 245 hectares has been affected by the virus. A quarantine is in place to try to prevent its spread.
Richard Whittington from the University of Sydney's faculty of veterinary science has been working with the industry to reduce the risk.
He said it was unknown what triggered an outbreak but there was a ''very strong possibility'' that unusual seasonal conditions - such as last week's heatwave - had reduced the oysters' immunity.
It might also have spread naturally in ocean currents, he said, or have been transported on the hulls of pleasure boats or in the ballast of commercial ships.
The outbreak, which poses no health risk to humans, comes less than a decade after the Hawkesbury's Sydney rock oyster crop was obliterated by the QX disease in 2005.
Dr Lewis said the NSW outbreak had not hit consumer confidence.
“We haven’t noticed any negative effects on sales,” he said.
“If anything, demand has been getting stronger.”
Demand for South Australian oysters currently exceeds supply.