An Australian oyster farmer has been left stunned after shellfish thieves stole $350,000 worth of his stock.

About 320 aquaculture bags packed with 400,000 juvenile oysters were taken from leases run by Latitude 31 Oyster Co.

Business owner Ryan Freeman said the alarm was raised when his team went to check their bags on Scotts Creek at Oxley Island, near Taree on the NSW Mid North Coast.

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“The first thing we noticed was that there was a heap of our oyster bags missing from a few of the lines,” Freeman told 7NEWS.com.au.

“We sort of just thought someone’s stolen some of our bags ... which is bad enough, but then as we started to go through and inspect a lot further, we noticed that they’d actually emptied all our other oyster bags as well.

“So it wasn’t just a small theft, it was quite substantial.”

The stock was taken from leases on the NSW Mid North Coast. Credit: Latitude 31 Oyster Co

Police were called in on Tuesday morning and estimated the value of stolen oysters to be about $350,000.

The oysters are not ready for immediate sale and will need to be grown for another four to six months.

“Unfortunately (the theft has) probably happened within the last month or so,” Freeman said.

“Because they’re juvenile oysters, we sort of set and forget.

“We’ll go put them out and we won’t see them for another two or three months until we go back to re-grade and thin them out as they grow.”

Ryan Freeman is searching for answers are oysters worth $350,000 were stolen. Credit: Latitude 31 Oyster Co

Freeman, who has run his business for six years, said it was another “kick in the guts” after a tough period for the industry which has battled through floods and QX disease, a seasonal sickness impacting Sydney rock oysters.

“It sort of didn’t dawn on me at first because I was in shock. I just couldn’t believe the volume that had been taken,” he said.

“It’s obviously a big operation to try and move three to four tonne of oyster.

“So this isn’t a small operation — like this is obviously targeted.

“Everyone’s doing it tough, but I just don’t think going and stealing from your fellow oyster farmer is the answer.”

NSW has about 230 oyster farming businesses and the industry produced about 70 million oysters worth $78 million at the farm gate in 2023-24.

An investigation is underway and anyone with information or vision that may help should contact Crime Stoppers.