Two men were subsequently charged with theft. One pleaded guilty in the Kaikohe District Court but the other has yet to enter a plea.
"We appreciate it when locals let us know they see something going on," Mrs Fleming said. She and her husband, and local residents, had seen people wade out at low tide or use a boat to take oysters from the farm.
"They know exactly where to go, where the oysters are and what to do," she added, although some claimed the oysters were 'feral', and taken off the farm's outer frames, not from the commercially cultivated stock.
Alan Brain, who has a farm in the Waikere Inlet and another at Te Puna, said the theft problem was decades old, widespread and costing farmers "tens of thousands of dollars." At times he slept in his boat to deter thieves.
"Because of where these farms are we can't have the same security and surveillance as other businesses. We can't lock our shop," he said.
He had caught and "dropped into the court system" at least 50 people over the years, while he believed larger-scale thefts were often commercial, effectively organised crime.