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A mystery illness is wiping out millions of Pacific oysters south-east of Hobart and commercial growers don’t know what's causing it.
For the last few years oyster production in Pipeclay Lagoon, between Cremorne and Clifton, has plummeted.
The leases in the prime growing areas span a patch of sea water nearly entirely surrounded by land.
Josh Poke from the Tasmanian Oyster Co. is one of five businesses based in the area.
In 2021 he noticed a big jump in oyster mortality rates.
“It's gotten worse year on year, " he said.
"There was a fairly steep decline of our mature oysters."
Mr Poke said the company has virtually emptied out its stock from Pipeclay Lagoon to focus on breeding in other parts of the state.
“Going from producing 700,000 to 800,000 dozen a year to pretty much nothing at the moment is a pretty big shock."
“Not just to us, but to other growers in the bay,” he said.
During the 1990s Pipeclay Lagoon was one of the state's most productive oyster farming areas.
Oyster grower Steve Calvert was part of that boom time.
He's been farming in the lagoon for 38 years and his production has dropped by nearly 80 per cent.
"We had a great run up until about three years ago when we noticed a lot of mortalities in the stock," he said.
"It happened since the influx of sea grass in the bay."
Stuart Hansson from Albatross Fishing said it's heartbreaking to see what's happened to the stock.
"I've been here for 18 years, on-growing 50 to 60mm oysters to fatten within six months.
"I can't put stock on now, because it's too volatile, it could die, " he said.
"It's costing me about $800 a day to get out of bed and go to work."
Mr Hansson expects he'll have to exit in the industry in the next six months if it can't find out what's causing the oyster mortalities.
Pacific Oyster Mortality Syndrome ruled out
This isn't the first time Pipeclay Lagoon has been a victim of mass oyster deaths.
The Pacific Oyster Mortality Syndrome (POMS) was detected in the area back in 2016.
The impact of the virus was catastrophic for the industry.
A program to selectively breed oysters for POMS resistance has been successful.
Mr Poke is fairly sure the virus isn't to blame for the recent production losses in Pipeclay Lagoon.
“We’ve had the bay tested twice in the last six months, " he said.
“Both times, there’s been a negative."
Frances Huddlestone is the industry development officer with Oysters Tasmania and she said further research and more investment is needed to investigate issues in the lagoon.
"From the references to environmental data we have, nothing stands out as being that much of a cause or a difference that's brought it on.
"We have good connections within universities and researchers," Ms Huddlestone said.
"So it's really about securing funding and taking that to the next step."
Virus outbreak in St Helens
For the first time POMS has been detected in St Helens on the state's East Coast.
Craig Lockwood from Lease 65 in Moulting Bay, farms across a number of sites in the area.
He noticed some unusual oyster deaths at one lease and sent samples away for testing.
"When we noted the deaths, we had peaks in temperatures through the day and low tides, " he said.
"Which we believe is linked to triggering the virus in its severity."
The breeding stock known as diploid oysters, haven't been affected, but the oysters that are infertile, have tested positive to POMS.
"Effectively 25 per cent of stock that goes into the market place has been eradicated with the click of your fingers."
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