The European mink, Mustela lutreola, is one of the least–known mustelids in Europe (Youngman, 1982; Camby, 1990; Saint–Girons 1991). The species is, moreover, declining in number and many populations have disappeared (Romanowski, 1990; Saint–Girons 1991; Rozhnov, 1993). Formerly, mink were widely distributed through Europe, but today are found only in some eastern European countries (Sidorovich, 1991; Maran, 1992; Tumanov, 1992), in a small area of southern France (Braun, 1990; Camby, 1990; C. Maizeret, unpublished results) and in northern Spain (Ruiz–Olmo & Palazón, 1991; Palazón & Ruiz–Olmo, 1992; Gosàlbez et al., 1995). Thus, Mustela lutreola is one of the five most endangered small carnivore taxa in the Palaearctic (Schreiber et al., 1989).
The European mink was recorded in Spain during the middle of the twentieth century (Rodriguez de Ondarra 1955). Subsequently, the species expanded to the south and east, following the main river basins, principally the Ebro river (Palazón & Ruiz–Olmo, 1995). Today Spain is the only area in the world where Mustela lutreola is not in decline. The arrival of mink in certain areas of Spain has presumably meant adaptation to a new environment: the Mediterranean ecosystem. Here, most of the rivers have no polecats, Mustela putoriusy American mink, Mustela vison, or otters, Lutra lutra (Delibes, 1990; Ruiz–Olmo & Delibes, 1998).