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HUNTING BAG AND HABITAT SELECTION BY THE AMERICAN MINK {NEOVISION VISON) IN NORTHEASTERN POLAND
M. Wojciuch-Ptoskonka
Department of Ecology, Wildlife Research and Ecotourism, Pedagogical University of Cracow, Krakow, Poland, martawojciuch@op.pl
Introduction
The presence of American mink in Poland was reported in the late 1950s (Ruprecht 1983). These animals were most likely the escapees from commercial breeding centres as well as migrants from the western part of the Former Soviet Union, where the species had been introduced as game animal. In Poland, American mink was placed on the list of game species in 2002. The statistics provided by hunters reported that from 2002 - 2009 the culling of this species ranged from 2100 to 3500 individuals. It has been pointed out that American mink exerts an adverse impact upon native mammalian, bird, amphibian and fish species (Ferreras and Macdonald 1999). The use of hunting with firearms is not an effective method for achieving a reduction in its population numbers. Using traps is a much more effective way to reduce the numbers of American mink (Bryce et al. 2011), given the fact that the Polish game law permits such an option. For this reason, the main objective of this study was to indicate the forest habitats where minks occur in high densities and where trapping should be carried out.
Study area and methods
The material for this study was obtained from hunting districts (n = 365) situated in the Regional State Forest Directorate in Olsztyn. The total area of hunting reviers there is 2.22 million hectares, of which 0.66 million hectares (29.7%) are forests, administered by 33 forest districts. In the area, there are numerous lakes, and rivers where fish-farming is carried out, and a dense network of small watercourses. The data on harvest and occurrence of American mink was obtained from hunting reports in particular hunting reviers over 5 hunting seasons (2004 -2009). The hunting bags from the districts were cumulated into annual figures for particular forest districts. The data on the proportions of habitat types of forests was obtained from the forest districts and used to establish the relationships between the proportions of habitat types of forests in these districts and the harvest fig-
ures for American mink, using a rectilinear regression and the Pearson regression coefficient. The rate of increase or decrease in hunting bag was calculated using the finite harvest growth rate (A = Ht+1/ Ht), where H is the value of the hunting bag in two consecutive hunting seasons.
Results and discussion
During six years of study, the annual harvest of American minks fluctuated between 494 - 745 individuals (i.e. 0.75 - 1.13 of these minks/1000 hectares of forests). During the initial three years of study (2004 - 2006) the average annual hunting bag was 529 animals/year. In the following three years (2007 -2009) the hunting bag was higher by 34.4% at 711 animals/year. The hunters' reports noted the presence of minks in all 33 forest districts but in 7 forest districts no hunting bags of minks were reported.
A significant correlation was found between the proportions of alder and riparian forests (x) in a given forest district and the level of hunting bag of mink (y) in the 2009/10 hunting season. The increase in the proportion of these two habitat types of forest in forest districts increased the content of the hunting bags of minks. The relationship is described by a rectilinear regression equation y = 0.149 + 0.222 x, r = 0.44, and the correlation coefficient is statistically significant (p = 0.049). In the material analyzed, the proportions of alder and riparian forests in particular forest districts fell into within the 1.47% -7.90% range, whereas the hunting bag ranged from 0.07 - 3.74 animals/1000 hectares of forest. This relationship is associated with the minks' semi-aquatic way of life. Both habitat-types of forests are situated chiefly in waterlogged areas in the valleys of rivers, water courses and bodies of water which provide very suitable living conditions for this predator. To hunters, the American mink is not an attractive game and is hunted when other game species are culled, mostly during individual hunting trips. For this reason, comparing the data on harvesting can adequately reflect the population dynamics in the study area. The finite growth population rate (A) calculated for harvests in two consecutive years ranged from 0.875 - 1.335, and 1.050 on average. This could mean that the mink population increased by an average of 5.0% per year.
At present, there are widespread discussions on the methods required to exterminate American minks in the valuable natural areas or those areas where minks cause major economic damage among fish and bird populations. The successful reduction in mink population numbers is achieved when their extermination is pursued non-stop and involves vast areas covering several thousand square kilometers (Bryce et al. 2011). Eliminating minks from small areas in the form of a single exercise leads to rapid re-colonization by migrating young individuals in just six months (Niemczynowicz et al. 2011). The results of this study suggest that that mink harvesting in northeastern Poland is lower than net annual population increase of this predator. For this reason, an additional method which could reduce the number of minks involves the use of traps operated non-stop, placed within alder and riparian forests, on the banks of water courses and other bodies of water, and on special rafts. These trapping exercises should be carried out in National Parks and in hunting reviers adjacent to the Parks. Such a program would require significant financial support which probably means its implementation in the years to come is not very likely.
REFERENCES
Bryce R., M. K. Olivier, L. Davies, H. Gray, J. Urguhart and X. Lambin. 2011. Turning back the tide of American mink invasion at an unprecedented scale through community participation and adaptive management. Biological Conservation. 144: 575-583.
Ferreras P. and D. W. Macdonald. 1999. The Impact of American Mink Muste-la vison on Water Birds in the Upper Thames. Journal of Applied Ecology. Vol. 36, No. 5 (Oct., 1999), P. 701-708.
Niemczynowicz A., M. Brzezinski and A. Zalewski. 2011. Aliens attack -population dynamics and density control of American mink Neovision
vision in four National Parks in Poland. 8th European Vertebrate Pest Man. Conference. Book of Ab-stracts: 27. Berlin, 26 - 30 Septem-ber 2011.
Ruprecht A., T. Buchalczyk i J. M. Wojcik. 1983. Wyst^powanie norek (Neovi-siona vison) w Polsce. Przegl^d Zoologiczny 27: 87 - 99.
