MARINE scientists are working overtime to identify a mystery illness that has decimated Port Stephens Pacific oyster crops.
Millions of Pacific oysters have died suddenly over the past two months. Almost all of a batch of a million juvenile Pacific oysters imported from Tasmania by fourth generation grower Geoff Diemar died recently.
“It doesn’t seem to matter if they are imported from interstate, produced at a local hatchery or are wild catch,” he said. “The ones that seem to be surviving best are the wild catch but it depends on where they are in the port.”
Pacific oysters are not sold from the port during summer. The disease does not appear to have affected other marine species, including the native Sydney rock oyster.
A NSW Food Authority spokeswoman said testing had shown there were no human health implications regarding water quality or the consumption of seafood from the area.
“Oysters, fish and other seafood remain safe to eat,” she said.
“The authority recommends people to always thoroughly cook any recreationally caught seafood.”
The Department of Primary Industries is also working with the Environment Protection Authority on the investigation.
Pacific oysters first appeared in Port Stephens in 1985 and have been grown legally in the port since 1989. The Pacific oyster industry employs dozens of growers and is worth about $5 million per annum.
A meeting between government agencies and growers is expected to be held when analytical test results come back in the next fortnight.
BIOSECURITY experts are scrambling to identify a mystery disease that has decimated Port Stephens’ multimillion-dollar Pacific oyster crops and sent several growers to the wall.
There are fears the port may have to be quarantined to prevent the disease spreading.
Hundreds of thousands of Pacific oysters have died since late last year.
‘‘We lost 600,000 oysters over a couple of weeks. We were struggling to find any live ones to be honest,’’ veteran Salamander Bay oyster grower Robert Diemar said.
‘‘We haven’t seen anything like it before.’’
Pacific oysters, which are worth about $3million to the Port Stephens oyster industry, had been recovering from a disease that swept through the region last year.
To date, it appears the latest disease has affected only hatchery-sourced Pacific oysters.
However, it is feared it may also attack prime Sydney rock oyster crops in the port.
‘‘It’s very frightening not only for the guys who are growing Pacific oysters, but also for the rest of us,’’ Port Stephens shellfish program chairman Don Burgoyne said.
‘‘If it was Pacific Oyster Mortality Syndrome we would have been quarantined by now.’’
Several farmers who had invested heavily in Pacific Oysters have been ruined by the disease. ‘‘It’s literally taken my business away; I don’t know what I’m going to do,’’ Andrew Richardson said.
‘‘There’s not much we can do but to diversify.
‘‘It’s going to take three years for Sydney rock oysters to grow.’’
A Department of Primary Industries spokeswoman said biosecurity and fisheries experts were working with growers to identify the cause of the mortalities.
Twenty batches of affected oysters had been tested at the Elizabeth Macarthur Agricultural Institute at Menangle since early last November, with all testing negative for the virus that causes Pacific Oyster Mortality Syndrome.
‘‘It is not clear yet what is causing the mortality event, it could be an environmental factor. In all submissions tested to date, there is no evidence of a disease consistent with a known infectious agent,’’ the spokeswoman said.
‘‘Therefore, without any evidence of an infectious disease, the department’s biosecurity and fisheries experts are unable to put in place quarantine measures.’’
The NSW Environment Protection Authority and the NSW Farmers Association have also been consulted.
The oyster population in parts of Beaufort County has been nearly wiped out by a massive die-off, and the area’s oyster farmers are feeling the pain, according to environmental officials and fishermen.
It’s difficult to say exactly how many oysters have died, but fishermen in Beaufort County are reporting as much as 75 to 90 percent of the oysters they find in the areas they harvest are dead, said Lee Taylor, S.C. Department of Natural Resources commercial shellfish coordinator.
“We don’t have official numbers right now because it varies even from one side of the river to another,” Taylor said.
It’s likely that heavy rain over the summer caused the deaths by inundating the estuaries where oysters grow with fresh water and lowering salinity levels, he said.
Along the banks of the Broad River, 80 to 90 percent of the oysters are dead, according to Craig Reaves, owner of Sea Eagle Market in Beaufort.
“Everywhere you look it’s just dead oysters,” he said. “Everything in that area is wiped out.”
Reaves has tested salinity levels in the river and gotten results near zero, he said. Where his fishermen once picked 1,000 single oysters in a day, they’re finding only about 100 living oysters now, Reaves said.
“It was during the summer that we had so much rain that our salinities got very out of whack,” he said. “But I’ve never seen so much rain that it would affect the oysters.”
Technically the state is at normal rain levels, but the rain fell hard enough and in a short enough span to have a lasting effect on salinity levels, Taylor said.
“We haven’t done an extensive survey yet, but there’s really not a whole lot we can do about it,” Taylor said. “We can’t increase salinity.”
Fisherman Jon Dusenberry picks clusters of oysters near Whale Branch and has seen between 75 and 90 percent of the oysters in the area near the Coosaw River dead. In the past, he’s sold his oysters to eight restaurants in Myrtle Beach, but he’s had to cut back to supplying just three this year, he said.
“That’s the first that’s happened to me in this area,” he said. “It’s kind of wiped us all out right here.”
It appears the worst of the deaths are in Reaves and Dusenberry’s areas along the Broad and Coosaw rivers, Taylor said. He has also heard from fisherman in one area near Charleston, but that die-off is not as large as in Beaufort County.
Although there is little DNR can do to stop the deaths, Taylor is documenting the event for study.
Of the oysters he has observed so far, Taylor said he’s found many with juvenile oysters attached to the inside of the shells, which means the oysters were able to reproduce at least once before they died.
However, it will still take some time for the population to recover, he said.
“It could have a long-term impact up to two or three years, but it’s hard to project,” Taylor said.