The effective number of alleles and also the number of private alleles found in mink caught on this river were the highest of all the study sites of feral mink. Our

results confirm our suspects that the mink population established on Butrón River at the beginning of the 1990s may be the origin of almost all the feral mink population of the study area (Zuberogoitia and Zabala 2003a). However, the colonisation process seemed to be slow, possibly due to the large number of geographic and anthropogenic barriers. The first observation made after Butrón was recorded in the neighbouring catchment of Urdaibai (the main this website river central points are 15 km apart) five years later, in 1995, and over the next ten years American mink became abundant in the Urdaibai basin. With the colonisation of the area by American mink and the increase in their

population, a decrease in numbers of European mink was observed. During a mink survey carried out in 1999–2000 in the Urdaibai catchment, we captured 11 European mink and no American mink (trapping effort = 1,609 trap-nights; Garin et al. 2002b), whilst in the winter of 2008–2009, i.e. after the invasion had occurred, we captured 13 American mink and only 3 European mink (trapping effort = 1,233 trap-nights). Obviously American mink displaced European mink and occupied NU7441 the same habitat. European mink populations collapsed, probably due to intraguild competition between the two species (see Maran et al. 1998; Sidorovich et al. 2010). On the other hand our models show that, besides the competition, the presence of barriers on the rivers and tributaries also has an effect on European and American mink occurrence within the study area. Both mink occurred more frequently Etoposide on those river stretches

which had the lowest number of barriers than in random locations, although European mink is probably more affected by habitat fragmentation than American mink, which seems to be more adaptable. In fact, the best model to explain European mink presence after AICc included the number of slight barriers as a explanatory variable whilst models for the American mink did not. This suggests that while American mink can cope with slight barriers and small dams in their territories, European mink are more affected by their negative effects. Mink can cross most of the barriers and can reach some highly altered streams but there are no long, good-quality, barrier-free stretches which facilitate persistence for long periods in these catchments. The high number of barriers and the high fragmentation level prevent populations from becoming established. The length of main river stretches between two fragmented areas and the low number of tributaries which are free from barriers are insufficient to meet the habitat selleck screening library requirements of one male mink (Zabala et al. 2006).