Feral Mink Research Articles

High mitochondrial DNA diversity of an introduced alien carnivore: comparison of feral and ranch American mink Neovison vison in Poland

AbstractAim Invasive alien species usually exhibit very high adaptation and rapid evolution in a new environment, but they often have low levels of genetic diversity (invasive species paradox). Genetic variation and population genetic structure of feral American mink, Neovison vison, in Poland was investigated to explain the invasion paradox and to assess current gene flow. Furthermore, the influence of mink farming on adaptation of the feral population was evaluated by comparing the genetic structure of feral and ranch mink.Location Samples from feral mink were collected in 11 study areas in northern and central Poland and from ranch mink at 10 farms distributed throughout the country.Methods A 373‐bp‐long mtDNA control region fragment was amplified from 276 feral and 166 ranch mink.Results Overall, 31 haplotypes, belonging to two groups from genetically diverse sources, were detected: 11 only in feral mink, 12 only in ranch mink and eight in both. The genetic differentiation of feral mink from the trapping sites was high, while that among ranch mink from various farms was moderate. There was no significant relationship between genetic and geographic distance. The number of trapping sites where given haplotypes occurred correlated with the number of farms with these haplotypes. The mink from two sites were the most divergent, both from all other feral mink and from ranch mink. Comparison of mtDNA and microsatellite differentiation suggests male‐biased dispersal in this species.Main conclusions American mink in Poland exhibit high genetic diversity and originate from different source populations of their native range. The process of colonization was triggered by numerous escapees from various farms and by immigrants from Belarus. The genetic structure of local feral mink populations was shaped by the founder effect and multiple introductions. The genomic admixture that occurred during mixing of different populations might have increased the fitness of individuals and accelerated the invasiveness of this species.

Toxoplasma gondii in feral American minks at the Maullín river, Chile

American mink (Neovison vison) is a widely distributed invasive species in southern Chile. Thirty four feral minks were trapped at two distinct sites (rural and peri-urban), diet analyzed and Toxoplasma gondii exposure compared using PCR and specific antibodies. Serum samples were evaluated using a commercial latex agglutination test where a titer ≥1:32 was considered positive. Of 30 mink analyzed, 21 (70%) were positive to T. gondii antibodies, with titers ranging from 1:32 to 1:2048. As expected, adult mink showed higher seroprevalence of exposure to T. gondii (18/21) than young mink (3/9) (P=0.008). There was not statistically significant difference between sex groups (P=0.687). Differences in seroprevalence were observed between the two sample sites with a higher proportion of positive individuals in the peri-urban area, and therefore, closer to human settlements (35.7% vs. 100%, P=0.0001). Individuals positive to T. gondii using PCR and/or serology showed similar differences by site with higher infected individuals in peri-urban areas (58.8% vs. 100%, P=0.007). Diet of American mink based in fecal composition analyses was mainly based on crustaceans (frequency of occurrence: crustaceans=100%, birds and rodents<7%), suggesting that the high observed prevalence of T. gondii infection might be more associated with its aquatic behavior (e.g. ingestion of oocysts in contaminated fresh water) than with their trophic behavior (e.g. preying over species that can have T. gondii cysts in their tissues). As an invasive species potentially subject to routine culling to maintain population sizes under control, minks could be used as a sentinel species to monitor pathogens of public and wildlife health importance, such as T. gondii, in aquatic environments.

Reliability of stained placental scar counts in farmed American mink and application to free-ranging mustelids

Abstract Despite the numerous studies carried out on the endangered European mink (Mustela lutreola) for conservation purposes, the reproductive biology of this species is largely unknown. In the wild reproductive parameters such as litter size are difficult to observe, particularly for cryptic species such as mustelids. We compared the reliability of nonstained and stained placental scar counts in farmed American mink (Neovison vison) with known litter sizes and then applied the best methodology to free-ranging related species—European mink, European polecat (Mustela putorius), and feral invasive American mink—for a comparative study of embryonic litter size in western Europe populations. The staining method allowed us to improve the detection of placental scars and to increase the reliability of the method by reducing the observer effect. Nevertheless, this analysis must be performed by 7 months postpartum, before the regeneration of uterine tissues. In free-ranging animals the mean embryonic litter siz...

Multiple introductions determine the genetic structure of an invasive species population: American mink Neovison vison in Poland

Genetic diversity of feral and ranch American mink was studied in order to understand the processes of invasion and the possible influence of multiple introductions on the feral mink population in Poland. Tissue samples obtained from feral mink taken from 10 sites across Poland (196) and from ranch mink at nine mink farms (147) were genotyped at 14 microsatellite loci. Genetic differentiation among the separate regions and sites indicated some restriction in gene flow among them (pairwise F ST values), and greater variation at microsatellite loci for feral mink was attributed to differences among sites rather than among regions (AMOVA). A Mantel test demonstrated a positive association of pairwise genetic and geographic distances. A total of five clusters of feral mink were identified and their spatial distribution partially reflected regional distribution, but also suggested that there were other factors (human-mediated propagule pressure) shaping mink genetic structure. Feral and ranch mink belong to two genetically separate clusters and an assignment test showed that 34 feral mink (17%) were assigned to the ranch mink clusters. The proportion of feral mink assigned to ranch mink clusters correlated with the size of the farm breeding stocks in the districts where sampling sites were located. High human-mediated propagule pressure (particularly in western Poland) increases feral population genetic diversity and overwhelms genetic structure and potential management units, making the control of mink populations less successful. Our results indicate that reducing number of escapees from farms should be required management action.

Estudio biométrico preliminar del dimorfismo sexual en visones americanos Neovison vison (Schreber, 1777) de granja y salvajes en el norte de la península ibérica.

The American mink is an invasive species throughout Europe where feral populations have become established in the natural environment due to escapes from fur farms or by intentional release. This study compares captive ranch mink with feral mink from nearby areas using basic biometric measures (weight, total length, body length and tail length) and the physical condition of individuals. We also analyze sexual dimorphism and address the various hypotheses on dimorphism to date. The degree of sexual dimorphism is also compared between the populations to identify any potential differences.

Have Patagonian waterfowl been affected by the introduction of the American mink Mustela vison?

The American mink Mustela vison has spread widely beyond its native North American range and is associated with problems for the conservation of native species because of its impact as both predator and competitor. We investigated the impact of feral mink on waterfowl in Lanín National Park, south-west Neuquén, Patagonia, Argentina, an area in which the predator is currently expanding. Statistically significant differences were observed in the number of waterfowl species at lakes without mink (7.3 ± SE 0.7) compared to those with mink (4.0 ± SE 0.6). Overall abundance of birds observed per day was higher at lakes without (104.2 ± SE 20.6) than with mink (21.2 ± SE 22.3). The great grebe Podiceps major, speckled teal Anas flavirostris, Chiloe wigeon Anas sibilatrix and red-gartered coot Fulica armillata were more abundant on water bodies without mink, and flocks of the ashy-headed goose Chloephaga poliocephala were larger in areas without mink. Other species, such as the white-tufted grebe Rollandia rolland, coscoroba swan Coscoroba coscoroba, black-necked swan Cygnus melanocoryphus, cinnamon teal Anas cyanoptera, Andean duck Oxyura jamaicensis and Andean gull Larus serranus were never observed in areas harbouring mink. We conclude that at least 12 of the 25 waterfowl species observed are sensitive to the presence of the mink, either being absent or having a lower abundance where mink are present.

Genetic variability of feral and ranch American minkNeovison vison in Poland

The diversity of 11 microsatellite loci was examined to estimate the genetic variability of ranch and feral American minkNeovison vison (Schreber, 1777) in Poland. Samples were collected from 10 mink farms (182 individuals) and from 5 areas in the north-eastern part of the country (87 individuals). At each examined locus the observed heterozygosity (H o) was lower than the expected heterozygosity (H e). Feral mink showed lower genetic variability than ranch mink; however, in the former group the mean value of the inbreeding coefficient (F IS=0.306) was higher than in the latter (0.242). These results demonstrated that feral and ranch mink belong to two genetically close but separate groups. Genetic differences were identified between mink colour breeds but not between animals from particular farms. The height of the modal values of ΔK indicated the presence of four genetic clusters: (1) farmed mink sapphire, (2) farmed mink standard and pastel, (3) farmed mink pearl and (4) feral mink. Assignment of mink individuals using assignment test, STRUCTURE and GeneClass 2.0. revealed that 12–16% of the feral mink group are likely to be ranch mink escapees. It may be concluded that approximately 30 years after the start of the expansion of feral mink in north-eastern Poland, this wild-living population exists without a major input of individuals bred on fur farms.

Evidence of admixture between differentiated genetic pools at a regional scale in an invasive carnivore

Invasive species represent a major threat to biodiversity, and the understanding of their population genetics is one of the most important goals in conservation biology. Recently, it has been proposed that methods using molecular tools could help define efficient eradication strategies and should be a preliminary step in the management process. The American mink was introduced in Europe for fur farming purposes in the 1920s, and, due to escapees, several feral populations have been mentioned in the last decades. In France, feral mink have been observed since the 1970s, and the largest population, located in Brittany, is considered to be still expanding. We investigated the genetic variability and population structure of 149 feral mink and 21 farmed mink from this area using six microsatellite loci. Our results showed three genetically distinct population units at the regional scale. A pattern of isolation by distance was observed for the whole sample. In our case we explain this pattern by recent admixture of the three genetic units. Our findings suggest that populations have recently met and started to homogenise.

Population genetic structure and distribution of introduced American mink (Mustela vison) in Spain, based on microsatellite variation

The population genetic structure of an invasive species in Spain, the American mink (Mustela vison), was investigated using microsatellite DNA markers. This semi-aquatic carnivore, originating from North America, was imported into Europe for fur farming since the beginning of the 20th century. Due to massive escapes, farm damages, deliberate releases and/or accidents, feral mink populations were established in the aquatic ecosystems of many European countries, including Spain. We genotyped 155 American mink originating from the Spanish regions Basque Country, Catalonia, Castilla-Leon, Aragon, Valencia and Galicia using 10 polymorphic microsatellite loci to highlight population genetic structure, distribution and dispersal. M. vison populations in Spain appear differentiated and not yet connected by gene flow. Bayesian clustering analyses and spatial analyses of molecular variance detected four inferred clusters, overall coinciding with the sampled geographical localities. Preliminary testing shows moderate to large estimated effective population sizes. Molecular analyses result useful to provide baseline data for further research on the evolution of invasive mink populations, as well as support local management strategies and indirectly benefit the conservation of threatened species in Spain, such as the endangered European mink (Mustela lutreola), and the polecat (Mustela putorius), which share the habitat with the American mink.

Assessing the potential for impacts by feral mink on wild mink in Canada

Invasive feral American mink ( Neovison vison) have had well-documented impacts in Europe and South America. We tested the hypotheses that escape of ranch-raised mink is also common in Canada where the species is endemic, and that declines of Canadian wild mink apparent from harvest data are related to mink ranching. Consistent with these hypotheses, we found positive relationships among Canadian provinces: between mink ranch density and mink harvest density; between ranch density and the density of ranch mink caught by trappers; and between mink harvest density and the density of trapped ranch mink. A multiple regression and variance partitioning demonstrated that the density of trapped ranch mink explained the largest component of unique variation in annual mink harvest by trappers per province. Moreover, the change in mink harvest by trappers per province estimated over a 30-year interval ( λ harvest) had a close, positive relationship ( R 2 = 0.92) to the change in ranch density estimated over the same interval ( λ ranch). Our analysis suggests that the conditions exist for feral mink to contribute to wild mink declines through outbreeding depression or the introduction of disease.

Demography of three populations of American mink Mustela vison in Europe

ABSTRACT Demographic data on an invasive species of management concern, the American mink, are presented. Data were obtained on three feral mink populations in Europe distinguished by differences in the time elapsed since population establishment. Demographic data are presented in the form of life tables, age–sex distributions and sex ratios. Mink lived a maximum of 6 years, and mortality of 1‐year‐olds and adults differed substantially between populations. The data support the hypothesis that mink populations subject to culling have a higher proportion of young (less than 1 year old) to adults compared with non‐culled populations.

An assessment of the local impact of native predators on an established population of British water voles ( Arvicola terrestris )

There is a considerable amount of literature on the diet and effect of feral American mink Mustela vison on the distribution and abundance of water voles Arvicola terrestris in Britain. Few recent studies, however, have attempted to examine the occurrence of water voles in the diets of native predators. Fox Vulpes vulpes scat and grey heron Ardea cinerea pellets were collected during winter 2003–2004 at a location known to contain a large number of water voles. These scats and pellets were subsequently analysed to determine the frequency of water vole occurrence in the diet of these opportunistic predators. Water vole remains were found in 30% of fox scats analysed and accounted for 13% of the total weight of scats. A total of 18% of heron pellets contained the fur of water voles in addition to the fur of four other rodent species. The potential role of native predators in the loss and fragmentation of site-specific populations of water voles in Britain is further discussed.

Effects of island isolation and feral mink removal on bird communities on small islands in the Baltic Sea

Summary Predation has been suggested as a major cause affecting survival, reproductive success and behaviour in vertebrate prey populations. The breeding season is a critical phase because the essential difference between selecting the proper nest site may be a question of breeding success and failure. Islands may serve as refuges for ground‐nesting birds against natural mammalian predators. However, many of the bird species breeding on islands are currently threatened by introduced predators because they may lack mechanisms to confront the threats of the new predator. We studied the combined effects of an introduced generalist predator, American mink (Mustela vison Schreb.), and island isolation and size on species richness, abundance and equitability of birds breeding on small islands in the outer archipelago of SW Finland, Baltic Sea. The study comprised two mink removal areas (one during 1993–2001 and the other during 1998–2001) and two comparable control areas (during 1994–2001 and 1998–2001), each covering 72–130 km2, of which between 1·07 and 1·27 km2 were land area. The mean island size in all areas was &lt; 2 ha. In the two control areas, both the species richness and abundance were highest on the most isolated islands, while isolation did not have obvious effects on these variables in mink removal areas. Species equitability was not influenced by mink removal or island isolation. The distribution of a maritime species, the razorbill (Alca torda L.), has changed dramatically: in the 1973–74, before mink invaded the area, the species was found commonly on less isolated islands than in 1994, after mink invasion. We suggest that in the presence of mink birds may have changed their breeding site selection and started to breed on the most isolated islands, which are not visited by mink as frequently as less isolated islands. Therefore, our results indicate that increasing island isolation may increase the number of bird species and their numbers, because island isolation slows down mink dispersal.

Dynamic impacts of feral mink predation on vole metapopulations in the outer archipelago of the Baltic Sea

Predation impacts by introduced predators are predicted to be most intense in island ecosystems, and also variable depending on environmental conditions, but large‐scale experimental field testing is rare. In this study we examine the factors that determine the distribution and abundance of vole metapopulations preyed upon by feral American mink Mustela vison in the outer Finnish archipelago of the Baltic Sea. Specifically, we follow the dynamics of field voles Microtus agrestis and bank voles Clethrionomys glareolus on 40 small islands under variable rainfall as part of a large‐scale mink removal experiment. For both vole species occupancy rates were negatively influenced by island isolation, as were extinction events for field voles. High summer rainfall in 1998 corresponded to large vole populations where mink were absent, populations that then crashed in 1999 and 2000 when below average rains fell during the summer breeding season. Where mink were present however, vole abundance remained more constant between years with no boom‐bust apparent. We conclude that weather and predation may drive vole abundance whereas habitat patchiness and metapopulation processes more strongly drive vole distributions. There may also be potential for interaction between these factors: because feral mink prevent rapid vole population growth after good summer rains, and vole dispersal is influenced by population size, feral mink may be changing vole dispersal patterns to disrupt the natural metapopulation dynamic. Hence this indirect impact of mink could lead to gradual erosion of vole populations in the outer archipelago by reducing recolonisation processes.

Effects of feral mink removal on seabirds, waders and passerines on small islands in the Baltic Sea

We studied the effects of removing introduced American mink (Mustela vison) on the number of birds breeding on small islands in the Baltic Sea. During autumn 1992–2001 mink were removed from a 72 km2 area, while mink were not removed from a 35 km2 control area. Second removal (125 km2) and control areas (130 km2) were established during 1998–2001. The breeding densities of ringed plover (Charadrius hiaticula), arctic skua (Stercorarius parasiticus), arctic tern (Sterna paradisaea) and rock pipit (Anthus petrosus) increased markedly in the removal areas in comparison to the control areas. Turnstone (Arenaria interpres), common gull (Larus canus) and wheatear (Oenanthe oenanthe) also appeared to increase. Two species already extinct in one of the removal areas, razorbill (Alca torda) and black guillemot (Cepphus grylle), returned to breed in the area. Breeding densities of great black-backed gull (Larus marinus), oystercatcher (Haematopus ostralegus) and white wagtail (Motacilla alba) were unaffected. We conclude that it is possible to remove feral mink from large archipelagos with many small islands, and that mink removal increases the breeding densities of many bird species in this habitat.

Variable responses of waterfowl breeding populations to long‐term removal of introduced American mink

It is suspected that feral American mink, an introduced predator in Europe, have seriously affected local densities of birds breeding in archipelagos and coastal areas. We studied the effects of mink removal on breeding densities of waterfowl in two manipulation and two control areas in the outer archipelago of SW Finland, Baltic Sea. The study was conducted in two phases: during 1992–2001 a total of 98 mink was removed from 60 islands and islets (total area 72 km2) whereas on 37 islands and islets (35 km2) mink was not removed. Additional mink removal and control areas were established during 1998–2001 to replicate the experiment. The breeding densities of the shelduck, tufted duck and the velvet scoter increased as a response to mink removal, while in the control areas their populations remained unchanged. The breeding densities of mallards increased during the first 7 yr of mink removal, but a steep decrease in the last study year resulted in a statistically non‐significant overall increase. The species with low breeding densities (the gadwall, northern shoveler, pintail and the red‐breasted merganser) increased as well. In contrast, the populations of large waterfowl species, the mute swan, greylag goose, common eider and the goosander, did not show obvious increases in breeding densities after mink removal. We conclude that feral mink may locally limit the breeding densities of some smaller waterfowl species and thus reduce the diversity of the waterfowl community in the outer archipelago.

Practical considerations for the field study of American mink Mustela vison in lowland England.

Because feral American mink are a successful alien carnivore worldwide, demands for field studies are likely to grow. Appropriate methods for trapping, use of anaesthesia, handling and radio-tracking are important from both academic and animal welfare view points. From accumulated field studies of mink over the last 30 years, including our own, we describe the problems that researchers will likely face in the field, and offer possible solutions for them. Surveys in the breeding and kit dispersal seasons likely inflate the estimated populations, and the best time to assess a local mink population is kit rearing season (May to July in the UK). The best trapping sites occur in the junction between a hedge/ditch and waterside cover. A mass of dry hay, with which the traps are wrapped, prevents mink from damaging their teeth. In the field mink is safely anaesthetised using a combination of a volatile agent (isoflurane), and injectable agents (medetomidine and ketamine mixture), which produces anaesthesia lasting for 60 minutes or more, and is reversible with another injectable agent (atipamezole). In lowland England triangulation is not necessary to locate animals by radio-tracking although obtaining radio signals is problematic when animals are under ground.

Decline in endangered species as an indication of anthropic pressures: the case of European mink Mustela lutreola Western population.

Populations of threatened species, especially predators at the top of the food chain, may be affected by anthropic pressures. The endangered western population of European mink Mustela lutreola has shown a large decline over 50% of its natural range. M. lutreola disappeared from northwestern France between 1984 and 1997, and the decline was associated with an increase in mustelid trapping, changes in watercourse quality, and habitat modifications due to agricultural practices. The pattern of decline showed a fragmentation restricting the minks into very small areas. Trapping was the first known cause of mortality. Although feral American mink Mustela vison may compete with autochthonous carnivores, M. lutreola had disappeared from streams before the introduction of the American species, suggesting that competitive interactions were not responsible. Furthermore, American mink has never been found or has remained rare in 62.4% of the area from which M. lutreola has disappeared. During the past 25 years, permanent grassland surfaces were reduced by 40%, whereas fodder culture increased by 470%, causing considerable habitat changes. Furthermore, 55.7% of water courses were classified as being of bad quality or polluted. Therefore, our data suggests that a conjunction of intensive trapping, alterations in water quality and habitat modification was critical for the European mink's decline. Although there are difficulties in ascribing specific cause to distribution changes in a top predator, this decline can be regarded as an indication for anthropic pressures on natural habitats.

Detection of Aleutian disease antibodies in feral American mink in southern England

Fourteen of 27 American mink (Mustela vison) trapped in the upper Thames region were positive for anti-Aleutian disease antibodies. This demonstration of the occurrence of this viral disease in a...

PCBs and Their Putative Effects on Polecat (Mustela putorius) Populations in Central Europe

In Europe polecat populations are declining for unknown reasons during the last decades. Data on the river otter, another mustelid predator, indicate that PCB levels are high enough in some populations to interfere with the reproduction of this aquatic species. Since the diet of the polecats consists to a large amount of aquatic prey (amphibians) it appears reasonable to assume that PCBs ingested with the prey are a factor in the decline of polecats. To test this assumption PCB residues in amphibians and in adipose tissue and liver of polecats from Southwest Germany were quantified and the results were compared with literature data on the reproductive toxicity of PCBs in feral mink. According to the current data total PCB levels in polecats (adipose tissue, mean 1244 ng/g lipids; liver, mean 1677 ng/g lipids) and their prey (frogs, mean 9279 ng/kg fresh weight; toads, 4948 ng/kg fresh weight) are comparatively low. Using the toxic equivalent approach, it was calculated that polecats could feed exclusively on amphibians without consuming a harmful amount of PCBs. Therefore, PCBs cannot be an agent currently affecting polecat populations in Central Europe. Other environmental factors like habitat destruction or road accidents are more likely to have a negative impact on polecat populations.