Assessment of the efficiency in trapping North American mink (Neovison vison) for population control in Patagonia

Abstract

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.

Marked Cards in the Pack: Using Playing Cards to Teach the Importance of Sample Size & Testing Assumptions in Capture–Recapture Estimations of Population Size

“…Three key points emerge. The first (commonly forgotten) is that trap success rates are often low in reality (e.g., Medina-Vogel et al, 2015), so using random number tables to determine trap success highlights this important point. The second point is that with low trapping intensity and poor trap success, it might not be possible to estimate population size at all.…”

Improving Trapping Efficiency for Control of American Mink (Neovison vison) in Patagonia

“…While much is known about mink behaviour and ecology in Britain and Europe [ 2 , 23 , 24 , 25 , 26 , 27 ] and various trapping protocols have been tested and established [ 28 , 29 , 30 , 31 , 32 , 33 , 34 ], there is scarce information available to determine best-practice control strategies for mink in Patagonia [ 11 , 35 , 36 , 37 , 38 , 39 ]. Thus, eradication of this widespread alien predator from mainland Patagonia is not likely to be cost-effective with currently available knowledge, techniques and funding [ 2 , 40 , 41 ]. Elimination of local populations in geographically discrete valleys may be possible if we can fine-tune our trapping techniques [ 9 , 42 , 43 ].…”

“…Trapping success is often higher for male mink than for females [ 22 , 41 , 57 , 58 ], especially in freshwater habitats [ 41 ]. We may be able to improve catch rates of females by increasing the density of traps.…”

“…We may be able to improve catch rates of females by increasing the density of traps. Some previous studies in Europe and in Patagonia have used trap spacings of 400–1000 m [ 31 , 33 , 41 , 59 ], and Roy et al [ 32 ] assumed an effective trapping radius of 250 m. With average female home range estimates varying between 0.5 and 6 km of river length [ 47 ], it was assumed that these trapping regimes would result in at least one trap per female home range, allowing all individuals to encounter a trap during the trapping period. However, mink spend most of their time in a smaller core area of their home range [ 47 , 50 ], making it less likely for females to encounter a trap on any given night.…”

“…If we increase trap density, the probability of trapping females is predicted to increase because males are removed, and because more trap-nights are available for females. Both Melero et al [ 47 ] and Medina-Vogel et al [ 41 ] recommended reducing the distance between traps to 200 m to maximize the number of minks trapped.…”