Oysters are a must on French dinner tables during the festive season, but shellfish farmers say climate change has caused production to plummet by up to 30 per cent.

Many French producers fear warming temperatures may force oyster farms to move north in search of cooler weather, possibly outside France.

Oyster production depends on cold winters when the shellfish “can rest and mature,” according to Yoann Thomas of the French Research Institute for Development.

Philippe Le Gal, head of the French shellfish producers’ association, said: “The warmer climate is beginning to have an impact. Oyster farmers are seeing volumes down by 20 to 30 per cent for 2018.”

Mr Le Gal told the AFP news agency that just a 10-gram decrease in the weight of each oyster brings down the price. France’s 4,500 oyster farmers sold about 100,000…