The White-clawed Crayfish, the only indigenous species of crayfish, was once sought after by the whole population because it was a refined and very accessible delicacy. Fishing pressure was not the only threat to this species. Water pollution, whether from discharges from sewage treatment plants or from run-off water laden with liquid manure and fertilisers, put additional pressure on populations. The species has even managed to adapt to habitat destruction and climate change. The final blow came with the arrival of the "crayfish plague" (aphanomycosis).
When infected, the muscular tissues are attacked by a fungus causing the death of the animal. A first epidemic, between 1878 and 1881, devastated a large part of the White-clawed Crayfish population. As the population was not recovering quickly enough in the eyes of some, exotic crayfish species were introduced. Whether these introductions were accidental or intentional, escaped from a laboratory or introduced by a restaurant owner remains a mystery. The fact remains that these introduced crayfish, the Signal Crayfish and the American Crayfish, sounded the death knell for the indigenous lake populations. Both are carriers of the plague without being affected by it. Voracious, more resistant and with a high reproductive capacity, they have managed to establish themselves in Lake Geneva. In 2016, nearly 13 tonnes of crayfish were caught, compared with 7 tonnes in 2012.
Today, every crayfish caught in Lake Geneva must be killed in order to restrict their proliferation. Eating crayfish is even encouraged to protect biodiversity!
And what has become of our indigenous species? Faced with such vultures from Lake Geneva, the White-clawed Crayfish has retreated to the waterways. Unfortunately, the Louisiana crayfish, with its beautiful orange colour, is beginning to invade these waterways. But that's another story....
Information taken from the book 1000 ans de pêche en Suisse romande.
