Laura Bonesi

Evaluation of sign surveys as a way to estimate the relative abundance of American mink (Mustela vison)

American mink Mustela vison are an invasive species in many parts of the world (e.g. Europe, Iceland and South America) and in many of these areas they are a threat to the native wildlife. It is therefore important to establish a reliable and efficient method to estimate their relative abundance in order to manage their populations. In this study, the use of surveys of signs (scats and footprints) as a way to estimate the relative abundance of American mink was evaluated. Populations of mink in three areas of England were studied to evaluate the impact of three factors (surveyor, marking places and month) on the probability of deposition and detection of signs. Among these factors only month had a significant effect. In the second part of the study, sign surveys were compared with live trapping and it was found that the proportion of sections with mink signs was only loosely correlated to the abundance of mink as estimated from live trapping. In conclusion, this study suggests that, provided that surveyors are trained, that there is a sufficient number of marking places in each section, and that the surveys are carried out in comparable seasons, sign surveys are an appropriate way to monitor the relative abundance of mink. Sign surveys are better than trapping when it is necessary to monitor mink populations over large areas because they are less time consuming, require less manpower and are cheaper.

Feeding habits of three sympatric mammals in NE Spain: the American mink, the spotted genet, and the Eurasian otter.

Diet composition, niche measures, and prey consumption of three sympatric species of carnivores, one non-native and introduced, the American minkNeovison vison Schreber, 1777, and two native, the spotted genetGenetta genetta Linnaeus, 1758 and the Eurasian otterLutra lutra Linnaeus, 1758, were studied in a Spanish Mediterranean area. The study was based on the analysis of prey remains in the faeces of the predators. Faeces of mink (n = 444), genet (n = 310), and otter (n = 108) were collected all year round for four years along the Llobregat (21 km) and Gavarresa rivers (12 km). Simultaneously, and in the same area, prey species density and weight were estimated by means of trapping. The diet of mink and genet was dominated by the American crayfishProcambarus clarkii, while the otter fed almost exclusively on fish. Compared to the mink, the genet seemed to specialise more on small mammals while the mink specialised more on aquatic birds, especially in autumn-winter. Niche overlap was higher between mink and genet than between either of them and the otter.

Relative abundance of culled and not culled American mink populations in northeast Spain and their potential distribution: are culling campaigns effective?

The effectiveness of culling campaigns to eradicate or limit populations of the alien, invasive American mink in Catalonia was studied by comparing the annual relative abundance of culled versus non-culled populations. We selected three populations that were culled under government campaigns and a fourth that served as a control and hence was left undisturbed (not culled). The study took place between 2002 and 2006 and annual relative abundances were estimated from trapping with bankside traps. The abundance of all four populations remained relatively stable throughout the study period. However, the annual relative abundance of the culled populations was lower than that of the non-culled population, which indicates that culling may have lowered the densities of mink, although eradication was not achieved. We also determined the potential distribution of the American mink in Catalonia by means of a habitat suitability model. The final aim was to assist in planning this species’ management. Almost all watercourses in Catalonia were identified as suitable for the American mink, with preferred areas located in the northeast. We recommend that the government and administrations promote culling campaigns focused on limiting the spread of the American mink as eradication is likely to be difficult to be achieved under the current situation. Target areas should be located on the edges of the American mink’s range and should be prioritized to limit the spread of this species to areas in which there are endangered native species.