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The European mink is a species of mustelid declared “critically endangered” nationally, with fewer than 500 individuals in the wild. The European Mink Association (AVE) indicates, for its part, that the American mink is an invasive mustelid catalogued in Spain and listed as one of the 100 worst invasive species worldwide. In addition, the otter and the polecat are protected, although the status of the latter in Spain is very uncertain, the entity points out. With this project, it is intended to update the distribution of the four species of mustelids and study the environmental and interspecific variables that determine this distribution. In addition, it seeks to know how the presence of one species can affect another (competition) or how some of the species coexist in the same territory and share the habitat, occupying different ecological niches.

The main objective of the project has been to update the data of the four species of mustelids, to show their current distribution and to study the environmental variables that determine their potential distribution.

• Establish a database model to collect all the data.
• Data collection between 2010 and 2019 of European mink in Spain.
• Data collection between 2010 and 2019 of American mink in Spain.
• To collect all known data on European polecat between 2010 and 2020.
• Compilation of data between 2010 and 2019 on Eurasian otters in Spain.
• Creation of the distribution map of the European mink in Spain.
• Creation of the distribution map of the American mink in Spain.
• Creation of the distribution map of the European polecat in Spain.
• Creation of the distribution map of the Eurasian otter in Spain.
• Establish the most important environmental variables.

The project has made it possible to obtain and analyse the presence data of the four species under study (European mink, American mink, otter and polecat) over 11 years (period 2010-2020), based on information provided by public administrations, associations, citizen science platforms, NGOs and individuals. The citations collected during the study were: captures in scientific studies or population monitoring, control and eradication captures, roadkills, observations, automatic photographs or videos, specimens killed by other causes, traces and indications such as footprints, excrement, markings, wallows, etc.

In addition, a sampling has been carried out in 22 areas as fieldwork to complement the information prior to this project. During this initiative, 19,132 citations of the four species have been collected between 2010 and 2020. The percentage of affection of the American mink towards the three native species has also been extracted: 90.4% in the European mink, 4.0% in the European polecat and 71.8% in the Eurasian otter, determining that the European mink is the species most affected by the presence of the American mink.

Some of the data to be highlighted in the project include:

• The compilation of 1,443 citations on the European mink, which occupies between 4.7 and 5.1% of the peninsular territory, in north-central Spain.
• The compilation of 27,175 citations on the American mink, whose distribution continues to advance in a southerly direction and with the possibility of connecting population centers.
• The compilation of 2,827 citations on the European polecat, which occupies between 13.1 and 14.1% of the peninsular territory, is distributed irregularly.
• The compilation of 7,689 citations on the Eurasian otter, which occupies 65.3% of the peninsular territory and continues to advance in an easterly and southeastern direction; in 3 – 4 years its distribution range has increased by 5%.
• Distance to rivers stands out as one of the most important variables to define the potential habitat of the European mink (27.9%), the American mink (41.3%) and the Eurasian otter (51.9%).
• Likewise, relative humidity, distance to tracks and distance to reservoirs were the most important variables to define the potential habitat of the European polecat (between 23 and 24%).
• The degree of contribution of the variable “presence of American mink” in the model of each species is 90.4 % in the European mink, 4.0 % in the European polecat and 71.8 % in the Eurasian otter.