The distribution of the Endangered southern roots had the highest IRR; most of the highly marked sprainting sites were found in this habitat. Canalized river otter Lontra provocax population in southern Chile has contracted, causing concern among otter specialists rivers and streams lacking these characteristics had the lowest IRR and hardly any highly marked sprainting sites. and conservationists. The main factor contributing to this decline is the loss of suitable habitat. Because the Chilean The data indicates that otters can tolerate some degree of riparian vegetation removal, provided there is minimum Irrigation Law promotes land drainage, the removal of riparian vegetation and canalization of lowland rivers in use of floodplains by humans. Temperate evergreen ombrophilus swamp forests and shallow watercourses several provinces, this situation could deteriorate further. Using an Index of Revisitation Rate (IRR), we assessed with woody debris or gravel, riparian vegetation and a plentiful supply of macrocrustaceans appear to be the the influence of woody debris, riparian vegetation, river bank morphology and river canalization on the use of preferred habitat and conditions for the otter and may be key to its survival in freshwater habitats. rivers and streams by the southern river otter. Surveys were conducted on foot, on a monthly basis, between April 1999 and March 2001 in the south of Chile. The Keywords Chile, Lontra provocax, macrocrustaceans, otter field signs, riparian vegetation, river canalization, surveys covered 13 sections of rivers and streams, 3 km long and <50 m wide. River and stream banks with high woody debris. density of riparian vegetation, woody debris and exposed disturbance and reduce the carrying capacity of their

Background: Introduced species can have a major negative impact on biodiversity; an example is the American mink, which was introduced in the 1930s in Patagonia. While there is a consensus that reversing alien mustelids continental scale invasions remains unfeasible, there is little consensus, given a maximum cost or investment, on the feasibility and efficiency of region-wide control or eradication. Thus, our goal was to provide information about efficiency for mink control in Patagonia. Methods: Between January 2009 and February 2013 this study was conducted in ten study sites (4 km to 15 km long) between 39°S to 45°S latitude. Minks were trapped using cage traps operated by two trappers. We estimated the population density at each study site assuming they were close populations, exhibit intrasexual territoriality and the home range of females were smaller than those of males. We obtained a theoretical population and a modeled population from our trapping results. Sixty five minks were trapped over 2190 trap nights (0.03 mink/trap night). Mink captures were higher in the first six days and in the first trapping campaigns. A two person team was able to control a maximum distance of approximately 6 km of river shore by foot and 15 km of sea and lake shores by boat. There was an over linear increase of operational costs as time passed. Our modeled population was 91% of the theoretical population. Conclusions: We believe that to trap and remove a minimum of 70% of the mink population in a region under ideal circumstances, traps should be deployed every 200 m and after the sixth day should be moved to another new transect. We suggest an annual repetition of this strategy as the more efficient for controlling mink populations in terms of trapping success and reduced costs. The number of traps will depend on the number of trappers participating and also on habitat characteristics.

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