France’s once-extinct wolf population has surpassed the 500 mark, making it “demographically viable” in a milestone hailed by conservationists but which farmers warn could see an exponential rise in attacks on their livestock.

European grey wolves were wiped out in France in the 1930s but in 1992, an alpha mating pair crossed the border from Italy. Since then, Canis lupus has spread throughout the Alps, across the Rhône valley into the Massif Central and up the eastern border of France to the Jura and Vosges mountains.

By 2016, it had reached the sparsely populated plains of eastern France, and there were even unconfirmed sightings in the Paris area.

But in the past six months, its reach has rocketed further from 74 to 85 “zones of permanent presence” with 72 packs of at least three individuals with the capacity to reproduce, according to France’s national office of hunting and wildlife, ONCFS.

The number of individuals has gone from 430 last winter to above 500, which “corresponds to the first level of demographic viability,” said ONCFS, adding that the figure was a target the government hoped to reach by 2023 in a five-year “wolf plan” launched early this year.