When talking about invasive animal species in Spain, the American mink ( Mustela vison ) is one of those that usually tops the list , along with the red crab or the Florida tortoise.
This small North American mammal was introduced to the Iberian Peninsula for fur exploitation purposes. It is a very prolific species with a great capacity for acclimatization to the environment: they adapt to almost any ecosystem present in mainland Spain.
The damage of their invasion
Minks are generalist carnivores, which can consume prey in the water, such as fish or crabs, and also on land – amphibians, reptiles, birds and small mammals. Hence the potential and risk of predation for other species, such as the water vole, the Pyrenean desman, the white-legged crab, the San Antonio frog or the midwife toad. But predation is not the only impact.
The American mink occupies the same ecological niches as, and competes with, the European mink ( Mustela lutreola ) . The American is stronger, more aggressive, and with more numerous litters, which has caused the displacement of native populations to the point of seriously endangering their survival. It also competes with other species such as the polecat, the stoat, the marten or the stone marten.
In addition to competition, many American mink are carriers of Aleutian disease , which they transmit to European mink and other small carnivores, weakening their populations and favoring their elimination. It has also been proven that they can be reservoirs or carriers of other pathogens, such as Toxoplasma or Leishmania , which can become zoonotic —that is, they can infect humans—.
The Great Liberation of 2001
The story that happened in La Puebla de Valverde, municipality of Teruel, on July 31, 2001, is well known. A group of activists from the self-styled Animal Liberation Front decided to enter a fur farm and open the cages, freeing 13,000 of the 20,000 specimens that were raised in it.
An event to which another similar one would be added in October 2006 in three farms in La Coruña —releasing another 15,000 animals— and in 2007, in Gerona —with 2,000 more animals—.
Many of the animals released in these acts of vandalism were successfully recaptured, many died in a few days, many run over, and many others hunted by foxes, eagles or other predators.
This result was relatively predictable, since these animals had never lived in the wild. However, a significant number of American mink managed to survive in the wild, reproduce successfully, form stable populations, and invade.
It is ironic that a group that claimed to move for animal welfare, was the cause of an invasion process that so negatively affects the biodiversity of the affected ecosystems. Many think that the event of 2001 was the trigger for the invasion of the American mink, but this is not true.
Sarrión’s minks: pioneers of the invasion?
During the summer of 1990, a farm in the municipality of Sarrión, Teruel, went bankrupt and released more than 8,000 specimens of American mink. The effects were similar to those of La Puebla de Valverde; many died, but the survivors formed a stable population that began to invade the region. This event, which happened a decade before the deliberate release of the animal activists, should have served as a warning of what was to come. However, they were not the first either.
In the vicinity of the Mero River, in Galicia, there have been populations of American mink since 1984 . The year coincides with the passage of the disastrous cyclone Hortensia, and it is not by chance; this tropical cyclone of historic proportions wiped out fur farms, causing the release of mink.
But the largest source of American mink in Spain did not come from a deliberate release, nor from an accident caused by a weather disaster. The largest population of American mink in the Iberian Peninsula was formed, not by a punctual and sudden release of a large number of individuals, but by the accidental introduction of a few specimens at a time, but sustained over time . And it is that the simple existence of this type of farms is already a risk factor for the invasion by American mink.
Because the animals can escape.
The American minks of Segovia
In the municipality of El Espinar, in Segovia, is the oldest American mink farm in Spain, founded in 1958 . Since the beginning of the 1960s, the presence of specimens in freedom began to be reported, coming from escapes from the farm. In the following years, there was a proliferation of small farms —many illegal—, and they acted as a source of specimens that continued to swell the wild population.
The constant escape of minks caused the wild population to cross the dispersion barrier, and spread progressively, becoming independent. It became the first invasive population of American mink in the Iberian Peninsula.
Currently, the population of American mink from Segovia has spread to the provinces of Valladolid, Ávila, Zamora, Cáceres, Toledo, Madrid and Guadalajara; In addition, other populations have been located in Teruel, Cuenca, Castellón and Valencia —from farms in Teruel—, in the four Galician provinces and in Catalonia. Finally, the presence of American mink has been reported in Cantabria, the Basque Country, Navarra, La Rioja, Zaragoza and throughout Castilla y León.
References:
Azami-Conesa, I. et al. 2021. Invasive Species as Hosts of Zoonotic Infections: The Case of American Mink (Neovison vison) and Leishmania infantum.
Microorganisms, 9(7), 1531. DOI: 10.3390/microorganisms9071531
BOE. 2013. Royal Decree 630/2013, of August 2, which regulates the Spanish Catalog of invasive alien species. BOE, 185(Sec. I.), 56764-56786.
Casals, F. et al. (Eds.). 2020. Guide to the invasive alien species of the rivers, lakes and estuaries of the Iberian Peninsula. LIFE INVASAQUA Project – Iberian Society of Ichthyology.
Melero, Y. et al. 2008. Space use and habitat preferences of the invasive American mink (Mustela vison) in a Mediterranean area. European Journal of Wildlife Research, 54(4), 609-617. DOI: 10.1007/s10344-008-0186-7
Vila, M. et al. (Eds.). 2008. Biological invasions. Superior Council of Scientific Research.
