A French shellfish farmer kept thieves at bay after they stole three tonnes of oysters.

       Christophe Guinot, 60, came up with a solution to stop the culprits: planting secret notes inside oyster shells to help the police track them down.

       Since Mr Guinot began planting the notes in 2016, he has not had any new incidents of oyster theft on his farm.

       “It has had a dissuasive effect,” the 60-year-old, from Leucate in southern France, told Reuters.

       Demand for oysters is high over the festive period, which is also a busy time for thieves.

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       Oysters are a lucrative dish. At one restaurant in central Paris, Chez Francoise, a dish of six high-grade oysters costs €24.

       Mr Guinot’s oyster farms are in a coastal lagoon near where France borders Spain. The oysters are reared in cages, and thieves are known to take boats out to the cages to pluck them from the water.

       However, Mr Guinot created a solution to tackle the problem: insert a tiny rolled-up note into an empty oyster and drop it back into the cage after glueing the shell back together.

       The note tells whoever opens the shell that they have won their own weight in oysters, and invites them to call to claim a prize.

       Cleverly, anyone who claims the prize is asked where they bought the oysters, and if it wasn’t from a place Mr Guinot usually supplies to, he notifies the police.

       Other shellfish farmers have begun to employ the same methods, and whilst no one has claimed a prize from Mr Guinot, some have been claimed from neighbouring farms, he said.

       This seems to have had a positive impact on levels of theft in the area. According to the French interior ministry, there were none last year, despite 19 oyster thefts taking place in 2017.