Are we able to affect the population structure of an invasive species through culling? A case study of the attempts to control the American mink population in the Northern Iberian Peninsula

The American mink (Neovison vison) is a semi-aquatic mustelid from North America that is considered an invasive species in many countries. Due to its reported damage to native species, efforts are often undertaken to eradicate or control these mink populations. The aims of this study were to describe the demographic structures of three mink populations subjected to different culling intensities, to detect possible variations in these structures caused by trapping and to identify possible efficient indicators of trapping efforts. From 1998 to 2011, a total of 1306 American mink collected during official culling operations in three different Spanish areas were submitted for study. We sexed the carcasses and removed a canine tooth from each animal during the post-mortem procedures. The incremental cementum lines of the teeth were used for age estimation. No evidence of age structure changes was detected in any population. The proportion of individuals in each sex and age class remained constant over time, suggesting that despite control efforts, the age structure remained stable over the study period. The population with the highest culling intensity has the highest sub-adult/adult ratio (1.51), and the catch per unit effort in this area was lower in the second part of the period, which is a possible indicator of reduced density. Age structure and sub-adult ratio might be useful indicators of successful trapping efforts. The results from this study could be useful for decision-making in conservation of native species and management of mink populations.