The scenario sounds like a bad B movie, “Attack of the Giant Coypu,” but that’s what’s happening right now in California. This giant ten-kilo rodent, capable of devouring entire fields and breaking through dikes, suddenly reappeared where it had been eradicated. Since 2017, US state biologists have been scratching their heads at the meteoric proliferation of nutria in the San Joaquin Valley. How could these animals, originally from South America, have come back in such proportions? Had they survived in hiding for forty years?
Through extensive genetic analysis, researchers discovered that the current specimens are unrelated to historic populations in California. On the contrary, their DNA matches almost perfectly with that of nutria living in central Oregon. The problem is that these animals are not long-distance migrants, and there is no record of their presence between Oregon and central California. The experts’ conclusion is therefore that someone transported them in a vehicle… to voluntarily release them there.
In a study published in Evolutionary Applications and relayed by Smithsonian Magazine, scientists from the California Department of Fish and Wildlife (CDFW) explain that this introduction is most certainly of human origin. Michael Buchalski, a geneticist at CDFW, points out the impossibility of natural migration: “It’s too far a distance, and we don’t find any coypu in the intermediate areas. This makes introduction by humans the most likely scenario.” This revelation changes the situation for the authorities, who are no longer fighting only against a species, but against the consequences of an illegal act.
So simple stupidity or sabotage? Some owners could have seen coypu as a natural and free solution for weeding aquatic plants in their private ponds. Others, more eccentric, could have simply fallen in love with the animal and decided to have a pet coypu. Finally, the hypothesis of a malicious act is not excluded: introducing a species capable of destroying the hydraulic infrastructure of an agricultural region is a formidable weapon for someone with malicious intent.
The orange-toothed scourge
The danger is very real. The coypu is not just a big, somewhat clumsy rat: it is capable of significant damage. With its bright orange incisors, it attacks the roots of the plants that maintain the banks. Even more serious, it digs complex networks of galleries in levees and earthen dams. In a California already weakened by cycles of intense droughts and torrential rains, these tunnels are time bombs. A dike weakened by rodents can give way at any time under water pressure.
Faced with this threat, the State has pulled out all the stops: thermal cameras, sniffer dogs and constant patrols. Since 2017, more than 7,800 individuals have been captured, but the battle is far from won. The cost of this “war” against the invader now amounts to approximately 5 million dollars (approximately 4.2 million euros) per year. A colossal budget to repair the error of one or a few individuals who perhaps thought they were doing the right thing, or who were simply seeking to do harm.
California law today authorizes citizens to hunt and kill these animals if they cause damage to their land, provided they immediately report the capture to the authorities. It is a general mobilization which is being organized to prevent the center of the State from becoming a giant Swiss cheese. Science has made it possible to trace the origin of the disease, but it is now a race against time to prevent these rodents from settling permanently in the Sacramento Delta.
Whether through ignorance or malice, the transportation of species remains one of the greatest threats to global biodiversity. In California, the “rat-pig” is a costly example.
