Content uploaded by Polina Nikova
Author content
All content in this area was uploaded by Polina Nikova on Nov 08, 2024
Content may be subject to copyright.
Citation: Nikova, P.K.;
Kachamakova, M.; Koshev, Y.
Assessing the Establishment of
American Mink (Neogale vison)
Escapees from the Fur Industry in
Bulgaria. Ecologies 2024,5, 610–626.
https://doi.org/10.3390/
ecologies5040036
Academic Editor: José
Ramón Arévalo Sierra
Received: 15 September 2024
Revised: 5 November 2024
Accepted: 5 November 2024
Published: 8 November 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
Assessing the Establishment of American Mink (Neogale vison)
Escapees from the Fur Industry in Bulgaria
Polina K. Nikova * , Maria Kachamakova and Yordan Koshev
Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1000 Sofia, Bulgaria;
maria.n.kachamakova@gmail.com (M.K.); bgsouslik@gmail.com (Y.K.)
*Correspondence: pknikova@gmail.com
Abstract: Mink farming has seen a resurgence in Bulgaria since 2013, and this has led to a high risk of
American mink escaping and establishing feral populations. The largest active commercial farm in
the country has a capacity of nearly 130,000 animals. The aims of this study were to gather first-hand
evidence of the presence of mink in the wild around the farm, assess their level of establishment,
and document the native species and local communities for future impact assessment. Surveys were
conducted using camera traps within a 3.7 km radius around the farm in the period 2020–2021 at
ten stations with 1943 realised trap-nights. Some early signs of the establishment of the American
mink in Bulgaria were documented. A large number of registrations was made, as frequently as the
Eurasian otter and golden jackal and more frequently than other mustelids in the study area. Mink
were observed throughout the two-year study, and escaped mink have been registered in the region
as early as 2017. These factors are interpreted as signs of the early stages of establishment. When
considering environmental, economic, public health, and social factors, we recommend that mink
farming should be banned in Bulgaria and further monitoring and management actions must be
undertaken for the individuals in the wild.
Keywords: invasive alien species; camera trap; circadian activity; naturalisation; fur farming; seasonality;
invasion pathway; escape from confinement; unintentional release; mammal monitoring
1. Introduction
An invasive alien species (IAS) that is frequently cited as having some of the largest
impacts on native biodiversity is the American mink (Neogale vison) (further referred to as
“mink”). It was recently renamed, formerly known as Neovison vison and Mustela vison [1].
The mink has been placed in lists of the most dangerous IAS concerning Europe [
2
] and
Russia [
3
]. A mustelid native to North America, the mink is a strict carnivore and a
generalist and opportunist predator [
4
]. Like other invasive alien mammals, the mink
has been introduced in Europe and other parts of the world via the fur industry [
5
–
9
].
Fur farming is its primary invasion pathway, by which it has escaped confinement and
established itself in Europe, South America, and Asia [
10
]. The mink is considered one of
the most widespread IAS in Europe [
11
]. Globally, the mink has established itself in at least
32 countries beyond its native range, with very few regions being free of its presence [12].
The rearing of mink in high densities in mink farms greatly increases the risk of zoono-
sis and transmitting infectious diseases, such as COVID-19 [
13
–
17
], leishmaniasis [
18
], avian
influenza A (H5N1) [
19
], and toxoplasmosis [
20
]. The risk of horizontal disease transmission
threatens not only humans but also native mustelids and other mammals [
21
–
23
]. Once they
escape into the wild, the mink’s negative impacts on native species also stem from their
trophic interactions with them. In Europe, the mink is considered a competitor of the
Eurasian otter Lutra lutra [
24
–
26
], European mink Mustela lutreola, and Eurasian polecat
M. putorius [
27
]. Simultaneously, their generalist diet also makes small mammals, ground-
nesting birds, amphibians, fish, rodents, crustaceans, insects, and molluscs vulnerable to
depredation [7,28–33].
Ecologies 2024,5, 610–626. https://doi.org/10.3390/ecologies5040036 https://www.mdpi.com/journal/ecologies
Ecologies 2024,5611
In Bulgaria, mink were imported for fur farming in the early 1950s [
34
], but there
is limited information on the scale of operations before the 21st century [
35
]. Other than
the farms, there are records of deliberate acclimatisation and release of mink [
34
], as well
as escapees being found by hunters [
35
]. There are no records on exactly when these old
fur farms closed down, but they might have done so around the same time as coypu fur
farms did—in 1989, when socio-economic changes in Bulgaria made this type of business
unprofitable [
36
]. As of 2013, there is a resurgence in mink farming in the country [
35
]. The
largest commercial fur farm has a capacity of nearly 130,000 animals [
37
]. There are only
a few other farms in Bulgaria that have a very limited capacity, especially in comparison
to the Madzherito farm [
35
]. Bulgaria had a peak of 150,000 exported furs in 2021 [
38
].
Multiple reliable records from local people showed that a large number of animals were
found in the nearby villages in the period 1 August 2017–11 March 2019 [
35
]. The majority
of these records were in the vicinity of the mink farm, and the records elsewhere were
likely escapees that had migrated further away in search of habitat with less intraspecific
competition. However, these published records were only from within human settlements,
so there is currently no data on the presence of this IAS in the wild. In light of these and
other social and ethical issues [
35
], the importation and breeding of mink in Bulgaria was
prohibited in July of 2022 [
39
,
40
]. After only two months, the government that produced
the ordinance dissolved and the Madzherito farm owner litigated the ban at the Supreme
Administrative Court, and mink fur farming resumed in Bulgaria [
41
]. As of the submission
of this manuscript, the legal case is still ongoing.
As the risks of mink farming are being disputed on a governmental level, there is a
great need for a scientific assessment of this issue. We need to know if there are mink in the
wild, how many are there, how frequently do they escape, are they forming self-sustaining
populations, and what effect are they expected to have on native biodiversity if there are
not any impacts already detectable. This kind of information is necessary in order to make
the best-informed management decisions going forward. The aims of this study were to
gather first-hand evidence of the presence of mink in the wild in the area around the largest
mink farm in Bulgaria, assess their level of establishment, and document the native species
composition for future impact assessment.
2. Materials and Methods
2.1. Study Area
The largest mink farm in Bulgaria is located less than a kilometre from the villages of
Madzherito and Zagore in Stara Zagora District (42.3488, 25.6548). The study area included
a radius of approx. 3.2 km around the mink farm. Their average annual dispersal rate
is 2–5 km [
25
,
42
]. The habitat is heterogeneous. The mink farm itself was assumed to
be the source of the mink, as there were no other establishments that kept mink in the
area and there was no historic data on the species being there prior to its construction.
It is part of a larger animal husbandry enterprise, and mink are fed offal left over from
poultry production. Northeast of the farm is the river Sazliyka. Approx. 3.7 km south is
the NATURA 2000 site of the same name. Northwest of the farm are artificial fish ponds,
and eastward and southward are rice fields with interspersed irrigation channels. North
and east of the farm are the villages Madzherito and Zagore, respectively.
2.2. Camera Trap Placement
The locations were defined by their microhabitat conditions and the frequency of
human presence: mink farm—the area immediately around the farm, where it was pre-
dicted that there would be a high density of recently escaped mink; fish farms—an area
of aquaculture farming, where there is high food availability attractive to non-established
mink that are not deterred by human presence; irrigation channels—artificially made water
courses that are somewhat disturbed by human agricultural activities; and river—the most
undisturbed habitat in the vicinity. The cameras (Table S1) were placed consistently at
10 locations called “stations” (n= 10), on animal paths mostly along a water body. This
Ecologies 2024,5612
opportunistic approach maximised detection, as they are rarely found beyond 100 m from
water [
43
–
45
]. The camera traps were checked, i.e., swapped memory cards and changed
batteries, on average once a month. The placement of the camera traps was limited by the
high risk of equipment theft and the negative perceptions of the mink farm owners towards
mink escape investigations. Regarding the limited number of camera trap deployments in
the river, the quantity of data suffered from equipment theft and illegal logging.
A total of 57 camera trap placements were made, where between 3 and 7 camera
traps were deployed at any one time (Table S2). The study was conducted in the period of
13 February 2020–21 September 2021, during which cameras were deployed for 586 calendar
days, though their image capture success was inconsistent (Figure S2). This accounted for a
total of 1943 trap-nights, where the timeframe calculated for each deployment was between
the date of placement and the date of the last captured image, not when the camera was
collected, to account for any technical issues (e.g., depleted battery, full memory) as well
as obstacles related to the COVID-19 lockdown during the study period. The cameras
took photos and 10 s videos alternatingly. The trap-nights were distributed between the
microhabitats as follows: mink farm, 118; fish farms, 1039; irrigation channels, 693; and
river, 93. Most of our camera trap deployments were concentrated at the Fish Farms because
the equipment was under limited surveillance by being on private land with permission
and the presence of the owner. Simultaneously, the fish farms are in an area where the
ecological, social and economic impacts of this IAS can be documented.
2.3. Mink Occurrence and Seasonality
Image captures with mink that were at least 5 min apart were labelled as registrations.
In order to account for uneven trapping effort, the results were represented as registrations
per 100 trap-nights per station. The dependence of mink detection on the distance from the
fur farm was also analysed using Spearman’s rank correlation test. When noting seasonality,
the cut-offs between seasons were taken as the 21 March, June, September, and December,
approximately when the solar equinoxes or solstices occur, representing winter, spring,
summer, and autumn, respectively. The results are presented as an extrapolation of mink
registrations per 100 days of the given season that could be observed with a camera trap,
called “trap season days”.
2.4. Measuring Circadian Activity
In the wild, mink are crepuscular or nocturnal animals that rest during the daytime in
den sites [
43
]. In captivity, they synchronise their activity with their feeding regimen, i.e., it
shifts from nocturnal to diurnal activity [
46
]. The mink at the farm were fed exclusively
during the day. Therefore, if nocturnal activity was prominent in escapees, then this
is interpreted as a sign of early establishment. The circadian cycle for each day was
determined by the average time the sun sets for each season. Graphing of the hourly
circadian activity was achieved using all mink observations, where an observation, for
example, within the third hour of the day was noted as any image captured between
02:00:00 h and 2:59:59 h.
2.5. Documenting the Presence of Other Species
All detected animals were manually identified to species, or at least to order in
some unclear cases. A list of all detected species was compiled and sorted into classes
(mammals, birds, and reptiles) and trophic relationships (competitor, prey, sympatric
carnivore, potential prey, and no relationship). Feral cats and dogs were excluded from
the data in order to focus on the impacts on wildlife. The competitors of the mink that
are still extant in Bulgaria are the Eurasian otter [
24
–
26
] and the Eurasian polecat [
27
,
47
].
They also compete with the Eurasian mink [
27
], but it has been extinct in Bulgaria since
the early 1950s [
48
]. The relationship between mink and the golden jackal (Canis aureus) is
uncertain, as American mink have not been reported to be part of their diet [
49
], so they
were noted as sympatric carnivores. Prey species were defined by having direct evidence
Ecologies 2024,5613
in the scientific literature that they have been found in the mink’s diet. The additional
grouping as potential prey was an attempt to cover the mink’s wide-ranging diet that may
not have been studied completely. All other detected bird species, except the predatory
Accipiter sp., Buteo buteo and Strigidae, were included as potential prey.
The incidence frequency of every species was calculated as the percentage of days
they were present from the total number of trap-nights per station. This information was
used to produce species accumulation curves (SACs) and sample completeness curves for
each station using the “iNEXT” v.3.0.0 package in R [
50
,
51
]. Using the incidence frequency
data of all identified species at each of the ten stations, the SACs were computed with
100 bootstrap replications and extrapolated up to 600 trap-nights.
The effects of mink on local fauna were assessed with correlation tests. The number
of mink registrations per 100 trap-nights was tested against total species richness and
species richness of prey, potential prey, sympatric carnivores, mammals, and birds. Reptiles
were excluded due to their rarity in the collected photo materials. The percentage of days
occupied by mink during the study was tested against the percentage of days occupied by
their competitor, the Eurasian otter, along with other mammals—golden jackals, European
badgers (Meles meles), beech martens (Martes foina), and coypus (Myocastor coypus).
2.6. Statistical Software
All formal analyses were performed using R version 4.2.2 (2022-10-31 ucrt)
Innocent and Trusting [
52
] with IDE RStudio 2022.07.2 Build 576 [
53
] and QGIS 3.22.12
Białowie˙
za [
54
]. Visualisations were made using the R packages “ggplot2” v.3.4.2. [
55
],
“devtools” v.2.4.5 [
56
], “ggpubr” v.0.6.0 [
57
], “ggpattern” [
58
] v.1.0.1, and “cowplot” v.1.1.1 [
59
].
3. Results
3.1. Distribution and Occurrence Frequency
Mink were observed in all sampled microhabitats, and there were a total of
123 observations representing 82 registrations (Figure 1; Table S2), which were made
on 55 out of 586 calendar days across the entire study area. In terms of distribution between
stations, the most mink registered per 100 trap-nights were at Station 1 (n = 11.0), followed
by Station 4 (n = 6.8) (Figure 2). No registrations were made at Stations 2, 7, and 8. Due
to the uneven sampling effort, no discrete distribution or density data could be provided.
With regard to microhabitats, it was most likely to observe mink at the irrigation channels,
followed by the area immediately around the mink farm (Table S3).
Ecologies 2024, 5, FOR PEER REVIEW 5
Figure 1. Example image captures of American mink (Neogale vison) around the largest commercial
mink farm in Bulgaria from different microhabitats and times of day. Two are from nighime (A,B)
and the other two from daytime (C,D).
Figure 1. Cont.
Ecologies 2024,5614
Ecologies 2024, 5, FOR PEER REVIEW 5
Figure 1. Example image captures of American mink (Neogale vison) around the largest commercial
mink farm in Bulgaria from different microhabitats and times of day. Two are from nighime (A,B)
and the other two from daytime (C,D).
Figure 1. Example image captures of American mink (Neogale vison) around the largest commercial
mink farm in Bulgaria from different microhabitats and times of day. Two are from nighttime (A,B)
and the other two from daytime (C,D).
Ecologies 2024, 5, FOR PEER REVIEW 6
Figure 2. Placement of camera trap stations and their trapping success in the study area around the
largest active mink farm in Bulgaria. Trapping success is represented as the number of registrations
of American mink per 100 trap-nights. The stations are categorised into four distinct microhabitats
based on the immediate environmental characteristics: mink farm (n = 5), fish farms (n = 31), irriga-
tion channels (n = 18), and river (n = 3). The camera deployments were regularly placed in the same
locations (stations; n = 10). An inset map of the study area in the Balkans is shown in the boom left
corner, where the area of the point is not proportional to the actual study area. Base map ©Open-
StreetMap OpenTopoMap (CC-BY-SA) and is available at hps://opentopomap.org/ (accessed on 7
November 2024).
3.2. Circadian Activity and Seasonality
Regarding the minks’ circadian activity in the area, it was more likely to observe a
mink during nighime (76.09%) (Table S3). With regard to their total circadian activity, it
seems to have one peak during the night between 2:00 h and 3:00 h, followed by another
peak around daybreak after 6:00 h (Figure 3). There were also two smaller daytime peaks
at around noon and before sunset. Another small peak was observed around midnight.
No activity was recorded between 8:00 h and 10:00 h or 18:00 h and 19:00 h. With regard
to seasonality, they were most active during autumn and least active during spring,
though this may be caused by unequal trapping effort between the seasons. There were
only two summer observations, which were made at noon. Peaks seem equivalent be-
tween seasons, but some deviation was observed during spring nights, when mink activ-
ity would peak only once before sunrise.
Figure 2. Placement of camera trap stations and their trapping success in the study area around the
largest active mink farm in Bulgaria. Trapping success is represented as the number of registrations
of American mink per 100 trap-nights. The stations are categorised into four distinct microhabitats
based on the immediate environmental characteristics: mink farm (n= 5), fish farms (n= 31),
irrigation channels (n= 18), and river (n= 3). The camera deployments were regularly placed in
the same locations (stations; n= 10). An inset map of the study area in the Balkans is shown in the
bottom left corner, where the area of the point is not proportional to the actual study area. Base
map ©OpenStreetMap OpenTopoMap (CC-BY-SA) and is available at https://opentopomap.org/
(accessed on 7 November 2024).
Ecologies 2024,5615
The number of mink that could have been observed per 100 days could not be predicted
by distance from the farm. The distribution of the distances was not normal (Shapiro–Wilk
normality test; W = 0.8825; p< 0.0327). A non-parametric Spearman’s rank correlation test
revealed no correlation between registrations/100 trap-nights and distance from the mink
farm (ρ=−0.0957; N = 57; p= 0.4791).
3.2. Circadian Activity and Seasonality
Regarding the minks’ circadian activity in the area, it was more likely to observe a
mink during nighttime (76.09%) (Table S3). With regard to their total circadian activity, it
seems to have one peak during the night between 2:00 h and 3:00 h, followed by another
peak around daybreak after 6:00 h (Figure 3). There were also two smaller daytime peaks
at around noon and before sunset. Another small peak was observed around midnight. No
activity was recorded between 8:00 h and 10:00 h or 18:00 h and 19:00 h. With regard to
seasonality, they were most active during autumn and least active during spring, though
this may be caused by unequal trapping effort between the seasons. There were only two
summer observations, which were made at noon. Peaks seem equivalent between seasons,
but some deviation was observed during spring nights, when mink activity would peak
only once before sunrise.
Ecologies 2024, 5, FOR PEER REVIEW 7
Figure 3. Hourly circadian activity of American mink in Bulgaria, showing total observed (n = 123)
and seasonal distribution.
Mink were mostly found during autumn (n = 25.5/100 trap season days), while it was
least likely to encounter them during the summer (n = 1.0/100 trap season days) (Figure
4). However, there were no image captures during summer for two of the microhabitats,
and there was a great number of images captured at the irrigation channels in autumn, so
the overall results for summer and autumn may be skewed by an undefined process or
error. There were no observations of mink at the fish farms during summer or at the river
during winter, while they could be observed throughout the year at the irrigation chan-
nels. The most mink by a large margin were found at the irrigation channels during au-
tumn (n = 60/100 trap season days). The second most likely time and place to find mink
was in the vicinity of the mink farm during autumn and winter (same value for both, n =
16.7/100 trap season days).
Figure 4. Frequency of American mink registrations at four distinct microhabitats and an average
between them across all seasons. Bars marked with an asterisk show where no camera trap data
were available.
3.3. Presence of Other Species
A total of 51 taxa were identified in the study area: 34 birds, 14 mammals, and 3 rep-
tiles (Table S4). Of these, 29 are protected under national law, 26 are protected under the
EU Habitats Directive, 20 under the Bern Convention, and 10 are included in the Bulgarian
Red Data Book. A taxon can be protected under multiple instruments. Of these, 20 taxa
Figure 3. Hourly circadian activity of American mink in Bulgaria, showing total observed (n = 123)
and seasonal distribution.
Mink were mostly found during autumn (n = 25.5/100 trap season days), while it was
least likely to encounter them during the summer (n = 1.0/100 trap season days) (Figure 4).
However, there were no image captures during summer for two of the microhabitats, and
there was a great number of images captured at the irrigation channels in autumn, so
the overall results for summer and autumn may be skewed by an undefined process or
error. There were no observations of mink at the fish farms during summer or at the river
during winter, while they could be observed throughout the year at the irrigation channels.
The most mink by a large margin were found at the irrigation channels during autumn
(n = 60/100 trap season days). The second most likely time and place to find mink
was in the vicinity of the mink farm during autumn and winter (same value for both,
n = 16.7/100 trap season days).
Ecologies 2024,5616
Ecologies 2024, 5, FOR PEER REVIEW 7
Figure 3. Hourly circadian activity of American mink in Bulgaria, showing total observed (n = 123)
and seasonal distribution.
Mink were mostly found during autumn (n = 25.5/100 trap season days), while it was
least likely to encounter them during the summer (n = 1.0/100 trap season days) (Figure
4). However, there were no image captures during summer for two of the microhabitats,
and there was a great number of images captured at the irrigation channels in autumn, so
the overall results for summer and autumn may be skewed by an undefined process or
error. There were no observations of mink at the fish farms during summer or at the river
during winter, while they could be observed throughout the year at the irrigation chan-
nels. The most mink by a large margin were found at the irrigation channels during au-
tumn (n = 60/100 trap season days). The second most likely time and place to find mink
was in the vicinity of the mink farm during autumn and winter (same value for both, n =
16.7/100 trap season days).
Figure 4. Frequency of American mink registrations at four distinct microhabitats and an average
between them across all seasons. Bars marked with an asterisk show where no camera trap data
were available.
3.3. Presence of Other Species
A total of 51 taxa were identified in the study area: 34 birds, 14 mammals, and 3 rep-
tiles (Table S4). Of these, 29 are protected under national law, 26 are protected under the
EU Habitats Directive, 20 under the Bern Convention, and 10 are included in the Bulgarian
Red Data Book. A taxon can be protected under multiple instruments. Of these, 20 taxa
Figure 4. Frequency of American mink registrations at four distinct microhabitats and an average
between them across all seasons. Bars marked with an asterisk show where no camera trap data were
available.
3.3. Presence of Other Species
A total of 51 taxa were identified in the study area: 34 birds, 14 mammals, and 3 reptiles
(Table S4). Of these, 29 are protected under national law, 26 are protected under the EU
Habitats Directive, 20 under the Bern Convention, and 10 are included in the Bulgarian Red
Data Book. A taxon can be protected under multiple instruments. Of these, 20 taxa were
reported in the literature as prey species, 18 were grouped as being potential prey, 9 were
sympatric carnivores, 3 had no trophic relationship, and 1 was a competitor species—the
Eurasian otter. The highest observed species richness was at Station 1 (29 species; Figure 5)
and the lowest at Station 2 (6 species; Figure 5). The sample coverage estimate of the
observed species at each station was >85% (Figure 5A,B) and their respective accumulation
curves approached asymptotes (Figure 5C,D). Rare species played a significant role in the
species composition of most stations.
With regard to the relationship between mink and other observed species in the
communities, it was found that mink registrations per 100 trap-nights were positively
correlated with total species richness (Spearman,
ρ
= 0.69; N = 10; p= 0.027), prey species
richness (Spearman,
ρ
= 0.83; N = 10; p= 0.003), and mammal species richness (Spearman,
ρ
= 0.65; N = 10; p= 0.044) (Figure S2). The correlation between mink registrations and the
percentage of days occupied by Eurasian otters was negative but very weak (Spearman,
ρ
=
−
0.13; N = 10; p= 0.72). Correlations with potential prey, sympatric carnivores, birds,
coypus, golden jacks, stone martens, and badgers were also not significant (p> 0.05).
Across the entire study area, the mink was the sixth most frequently observed animal
based on the sum of days it has been observed (n = 55 out of a total of 586 calendar days
when cameras had been deployed for the entire study), followed by the otter (n = 60),
mallard duck (Anas platyrhynchos; n = 72), coypu (Myocastor coypus; n = 87), mice and rats
(Muridae; n = 147) and Eurasian magpie (Pica pica; n = 148). Compared to other mammalian
sympatric carnivores, the mink was nearly as frequently found as the golden jackal (Canis
aureus; n = 54), and it was seen for more days than the stone marten (Martes foina; n = 36),
red fox (Vulpes vulpes; n = 17), Eurasian badger (Meles meles; n = 7), and European wildcat
(Felis silvestris; n = 5). There were no records of the Eurasian polecat, the mink’s other extant
competitor species in Bulgaria, though this was expected given their range [60].
Ecologies 2024,5617
Ecologies 2024, 5, FOR PEER REVIEW 9
Figure 5. Sample completeness curves (A,B) and species accumulation curves for Hill numbers 0, 1,
and 2 (C,D) for the observed species richness at camera trap stations (n = 10) placed around the
largest commercial mink fur farm in Bulgaria. Only five stations were ploed per graph for clarity.
Solid lines represent rarefaction curves and dashed lines—extrapolations. Shaded areas represent
95% confidence intervals.
4. Discussion
4.1. Distribution and Dispersal
From the camera trap survey presented in this study that was carried out in the pe-
riod 2020–2021, it was found that mink were consistently present in the area around the
fur farm near Madzherito Village, Bulgaria. Furthermore, the species has been docu-
mented since at least 2017 [35], and there have been nine registrations of mink roadkill
Figure 5. Sample completeness curves (A,B) and species accumulation curves for Hill numbers 0,
1, and 2 (C,D) for the observed species richness at camera trap stations (n = 10) placed around the
largest commercial mink fur farm in Bulgaria. Only five stations were plotted per graph for clarity.
Solid lines represent rarefaction curves and dashed lines—extrapolations. Shaded areas represent
95% confidence intervals.
4. Discussion
4.1. Distribution and Dispersal
From the camera trap survey presented in this study that was carried out in the period
2020–2021, it was found that mink were consistently present in the area around the fur
farm near Madzherito Village, Bulgaria. Furthermore, the species has been documented
Ecologies 2024,5618
since at least 2017 [
35
], and there have been nine registrations of mink roadkill casualties
in the region on a national database hosted by the Bulgarian Society for the Protection of
Birds—SmartBirds.org between 2021 and 2023. Therefore, it is reasonable to conclude that
the mink is invading Bulgaria using the unintentional invasion pathway in the category of
“Escape from confinement”, subcategory “Fur farms” [
61
,
62
], and that the farm presents a
significant risk for native biodiversity that needs to be addressed immediately.
Mink territories are usually estimated as linear lengths of an occupied riparian habitat
and range from approx. 6 km for males and 3 km for females, where a male’s territory
usually overlaps with that of one or more females [
63
]. Other papers cite their invasive
home ranges to be slightly over 1 km [
28
]. Therefore, the study area of a 3.2 km radius
around the farm could have encompassed several mink territories, but the number of mink
registrations was much higher than what would be generally expected. Adult dispersal
has been documented to extend up to 6 km and can occur several times per season [
64
,
65
].
On the other hand, juveniles have a greater propensity for dispersal, where they are known
to travel 10–50 km away from their natal home range during their mating season or in
autumn [
7
,
63
,
66
–
69
]. On a regional level, the mink’s average dispersal rate is 2–5 km per
annum [
25
,
42
]. The frequent escape of mink since at least 2017 calls for future studies that
greatly extend the radius of the study area to be able to track the invasion front.
4.2. Seasonal Activity
A high occurrence of mink was observed in the immediate vicinity around the farm in
autumn. The high recorded autumnal activity coincides with the mink’s kit-dispersal and
early overwintering seasons [
63
,
70
]. Higher autumnal population peaks were also observed
in Greece [
71
]. Other reports have documented mink populations to be higher in spring
rather than autumn [
35
,
63
,
72
], while in the northeastern Iberian Peninsula their activity
peaks in winter [
73
]. This discrepancy may be due to the different sampling methods, or
there could be a difference in the mink’s population dynamics between the north and south
European climates. The observed low activity in summer was likely skewed by reduced
trapping effort. The low activity observed during winter may be due to their short fur and
high surface-area-to-volume ratio, making mink more vulnerable to low temperatures than
native mammals of similar size [74,75].
4.3. Circadian Activity
Mink in Bulgaria showed several peaks in activity, where the largest ones were during
the night. The predominantly nocturnal activity is congruent with previous data on well-
established populations in Europe [
43
,
64
,
76
,
77
]. On the other hand, there are also records
showing diurnal activity in well-established populations in Spain [
75
,
78
], Finland [
79
], and
Slovakia [
80
]. The multitude of peaks that were recorded here shows some uncertainty in
the circadian activity of the mink, which could be due to a large proportion of them being
escapees from the farm in different stages of becoming established. However, the mink’s
circadian activity in its invasive range may need further study.
4.4. Establishment
With the available data, could the mink be considered an established species in
Bulgaria? With regard to neighbouring countries, there are established populations in
Greece [
81
,
82
] and Romania [
83
,
84
]. The establishment of the mink in countries north and
south of Bulgaria provides some evidence that the country offers a suitable habitat for
the mink to establish here as well. The primary evidence of establishment is, of course,
reproduction in the wild [
85
]; however, this can be difficult to observe, including in mink,
where neither juvenile mink nor other mammals were recorded during this study. It should
also be noted that there is not a universally accepted methodology for determining the level
of establishment of IAS [
86
], and neither has one been developed specifically for the mink.
In some cases, indirect evidence is enough to conclude whether the mink is established
or not. One method that has been used in countries where the species is believed to have
Ecologies 2024,5619
been established is the necropsy of female mink and performing isotope analysis of teeth to
determine diet, age, and reproductive status [
87
]. Other methods have used body length
and detection of tetracycline as fluorescent marking of their canine teeth [88].
In the current case, even if the mink are not reproducing in the wild, the effect of the
constant flow of individuals in the environment that we have registered is comparable with
that of a self-sustaining population. Furthermore, this could also increase genetic diversity
and enhance adaptation to living in the wild [
88
]. The impact could be even bigger as
the number of animals is not subjected to natural regulation as if it were a self-sustaining
population. The presence of animals for a long period after a fur farm has closed is also
considered a sign of establishment [
42
,
83
], but in this case, this is not applicable. In some
other cases, the mass presence of mink in the region around a fur farm or at long distances
away from it without any other farms nearby (16 km) [
82
] or straightforward survey data
are considered definitive evidence for establishment without direct data on reproduction in
the wild [
81
]. In Greece, the species was declared as established after collecting 86 records
from surveys in the span of 11 years in a region where 250,000–1 million mink are kept in
farms [82].
Several signs for the establishment of the mink in Bulgaria were documented. Firstly,
a large number of mink was registered from our observations (n = 82). Secondly, they
were found about as frequently as their competitor, the Eurasian otter, and other sympatric
carnivores like the golden jackal, and more frequently than other mustelids in the area.
Thirdly, the majority of mink observations were made during the night, which was a
deviation from their regimen in the fur farm, where they were fed exclusively during the
day. Fourthly, they were found in habitats without human presence, suggesting that some
have become avoidant of humans in comparison to their daily interactions with the workers
at the fur farm [
28
,
77
]. Fifthly, the observations were consistent throughout the two-year
study. Further considering other occurrence data and that there are reliable observations of
females with young in the wild by locals [
35
], we consider the mink to be in its early stages
of establishment in Bulgaria.
4.5. Potential Impacts on Native Species
The diversity investigation was carried out primarily for documentation purposes, as
there was no historical data available for comparison to estimate impacts, though some
inferences could still be made. The farm itself was in close proximity to a NATURA 2000 site,
and it is interesting that there is a tendency for this to be the case in other countries in
Southern Europe, but the impacts of escaped mink on these protected areas are largely
understudied [82].
Mink have a wide-ranging and adaptive diet, as the components and proportions
of animal species or even groups they predate on vary widely in their introduced ranges
and between seasons [
26
,
28
,
30
–
33
,
65
,
89
–
94
]. Their impacts on native fauna can also be
rapid and severe [
5
]. We found that mink prefer habitats with higher diversity of their
prey. This result is similar to other conclusions that their distribution is dependent on
prey availability [
77
], though their tendency to prefer greater species richness, in general,
may lead to greater impacts on native fauna in the study area and beyond. It must be
noted that the documented species assemblages of the observed riparian communities
were incomplete as the camera traps could mostly photograph medium-to-large terrestrial
species. Therefore, no impacts could be estimated for fish, crustaceans, or amphibians,
and most small mammals and reptiles must have also remained undetected. The effect
mink would have on every detected native species was not documented in the literature.
In order to account for this, we assessed the correlation between mink occurrence and a
grouping of potential prey species that did not have direct evidence for depredation by
mink in the literature, though it did not show a significant effect. However, it was notable
that the majority of the recorded species in the area were protected under multiple pieces
of legislation.
Ecologies 2024,5620
The mink’s impacts on native fauna have been extensively studied in the water vole
(Arvicola amphibius). Even after only a few months of the introduction of a single mink,
the native water vole population crashed in lowland England [
95
], but this, of course,
was not the only factor that contributed to their decline [
96
]. Similar rapid outcomes
of mink introduction have been documented in Belarus [
97
]. We found no evidence of
water voles, despite their presence being well known in the area [
60
,
98
]. This may mean
that consequences have already occurred in the region since the first reports of escaped
individuals from the Madzherito fur farm in 2017, though it would need to be further
researched using other methods.
Apart from being as frequently detected as the Eurasian otter, our data shows that
the mink did not have any detectable interactions with it. In the literature, the species are
suggested to be antagonistic towards each other [
25
,
26
,
99
,
100
], where some publications
state that the otter even repels the mink by being the stronger competitor of the two because
they are larger and more specialised in hunting underwater [
24
,
26
]. Other sources provide
data that there is limited niche overlap between the two species [
28
]. Most recently, it
has been argued that previously observed effects are actually within expected variation
for the species, i.e., there is no causal relationship between otter and mink population
variation [
70
]. The presence of otters may not prevent the establishment of mink; however,
avoidance behaviours are performed by mink when otters are present [70].
Another consideration for the potential impacts of the American mink is that it can
prevent the return of the European mink (Mustela lutreola) to Bulgaria. The European mink
is another mustelid competitor to the American mink; however, unlike the otter, it has
been proven to be a weaker competitor than its American congener [
27
,
91
,
101
,
102
]. The
spread of the American mink is considered one of the key factors in the decline of the
native European mink throughout its range [
47
,
101
,
103
,
104
]. Their decline is also believed
to be influenced by the transmission of the Aleutian mink disease virus from the American
mink [
22
], and the virus is also known to affect other native predators [
21
,
22
,
105
–
107
]. The
European mink has been extinct in the country since the early 1950s [
108
], and any future
plans for its reintroduction would be thwarted if the American mink definitively establishes
and spreads in Bulgaria.
4.6. Other Considerations
Mink pose an economic risk to the local fish farms, especially during winter. Similar
impacts have been noted in northern Germany [
32
]. While the otter can be deterred from
entering the fish farms using electric fences, this is not applicable for the smaller mink.
Furthermore, the impacts on the livelihoods of local people should not be neglected. The
fur farm emits a strong pungent odour, and escaped mink kill entire coups of family-owned
chickens. These disturbances have affected local people in the adjacent villages to the point
that some have emigrated to live elsewhere and housing prices have dropped in the area
(Koshev 2019, pers. comms. with locals). Furthermore, rearing mink in high densities
poses a significant health risk to both humans and native fauna. Recent examples of the
consequences of poor biosecurity at mink fur farms are the permanent cessation of mink
fur production in the Netherlands and a temporary stop in Denmark due to SARS-CoV-2
outbreaks in mink and from them into humans [
23
]. Another major concern for mink
for farming is the ethical aspects of rearing undomesticated animals in conditions that
are well documented to not satisfy any of the “Five Freedoms” and do not offer a “Life
worth Living” [
109
,
110
]. The conditions in which mink in fur farms are kept are not in
accordance with Council Directive 98/58/EC, which stipulates: “No animal shall be kept
for farming purposes unless it can reasonably be expected, on the basis of its genotype or
phenotype, that it can be kept without detrimental effect on its health or welfare”. All these
additional considerations presented here demonstrate that the issue of mink fur farming is
multidimensional and requires appropriate and swift management.
Ecologies 2024,5621
4.7. Future Management
This case presents two aspects that require management—the source population of
mink within the fur farm and the escaped mink in the wild. With regard to the farm,
the owners have stated that they have undertaken all measures possible; however, the
evidence presented here demonstrates that either the animals are continuously escaping
or they already have viable populations in the wild. Therefore, the limited measures
applied by the owners are ineffective, and the best solutions might be the closure of the fur
farm and banning mink fur farming in its entirety. While attempts to restrict fur farming
on a national level are ongoing [
39
,
111
], on a European level, the fur farming and trade
sector have impeded the inclusion of the American mink in the List of Invasive Alien
Species of Union Concern of the European Union’s Invasive Alien Species Regulation
№
1143/2014 [
12
,
112
]. However, there are attempts at achieving this goal through other means,
such as the ‘Fur Free Europe’ citizen’s initiative [
113
]. The opinions of stakeholders and
policymakers on this issue must be better informed from the available scientific literature and
reliable reporting on local impacts before any effective solutions can be enacted.
With regard to the escaped mink, we believe that the risk for a population to establish
in Bulgaria is significant. Future actions, other than changes in legislation regarding mink
fur farming, would include a better understanding of their current extent and further
search for signs of breeding [
85
,
87
,
88
], followed by regular monitoring, modelling future
spread, and using that information for appropriate trapping [
71
,
114
]. Mink monitoring
should also be carried out in parallel with monitoring of native species in areas where they
are discovered in order to document any impacts. As there is a lack of biodiversity data
for this region, the data provided here can be a benchmark. Such actions are necessary
for effective management [
115
]. Furthermore, local people should be educated to identify
this species to ensure effective reporting and potentially involve hunters in management
actions [
42
,
72
,
116
]. We acknowledge that a potential closure of fur farms may impact
the livelihoods of former workers; however, the context involves primarily one large
company with few local employees. These risks need to be compared with those posed by
fur farming.
5. Conclusions
In this study, we offer evidence that the American mink is constantly present in the
riparian ecosystem in the vicinity of the largest commercial mink farm in Bulgaria. We also
believe to have observed early signs of establishment, which further calls for immediate
action. American mink farming is a major risk to biodiversity and public health, raises
serious ethical concerns, and impacts the livelihoods of local people. Measures should be
undertaken as soon as possible to prevent further escape and control the escaped mink to
prevent the establishment of a viable population in the wild.
Supplementary Materials: The following supporting information can be downloaded at:
https://www.mdpi.com/article/10.3390/ecologies5040036/s1, Table S1: Camera specifications and
duration of deployment, Table S2: Table of localities and camera trap success, Figure S1: Camera
trap deployment chart, Table S3: Camera trap deployment success per microhabitat, Table S4: Local
biodiversity list showing all taxa identified during the study along with the pieces of legislation that
protect each taxon. The trophic relationship between each taxon with the American mink is also
noted along with the appropriate references, Figure S2 Species relationships correlations represented
by eleven scatter plots of Spearman’s rank correlation tests between mink registration frequency and
occurrences of animal groups and select species. Black dots indicate point data, the regression lines
are in black with grey shading for their 95% CI.
Author Contributions: P.K.N.: Writing—original draft; Data curation; Formal analysis; Investigation;
Methodology. M.K.: Conceptualization; Writing—review and editing; Investigation. Y.K.: Concep-
tualization; Writing—review and editing; Investigation; Methodology; Supervision; Validation. All
authors have read and agreed to the published version of the manuscript.
Ecologies 2024,5622
Funding: This study was conducted within the framework of the National Science Programme
‘Environmental Protection and Reduction of Risks of Adverse Events and Natural Disasters’, approved
by the Resolution of the Council of Ministers No. 577/17.08.2018 without financial support. The
research presented here was entirely self-funded by the authors. The authors declare no competing
financial or non-financial interests.
Institutional Review Board Statement: Not applicable as the methods involved remote sensing via
camera traps.
Informed Consent Statement: Not applicable.
Data Availability Statement: The original contributions presented in the study are included in the
article and Supplementary Materials; further inquiries can be directed to the corresponding author.
Acknowledgments: The authors are grateful to B. Dimitrova, K. Angelova, and R. Markova for
participating in the identification of species during camera image processing. The authors would
also like to extend their thanks to S. Stefanov (Institute of Astronomy at the Bulgarian Academy of
Sciences) for writing a simple program that greatly helped with data input. The authors would like to
express gratitude towards T. Dimitrov, M. Peneva, and S. Uzunov for the provided technical support.
The authors are also grateful to G. Nonev for his overall help during field research. The authors are
also thankful to the contributors of the SmartBirds.org database. The authors thank the reviewers
for their contributions to this publication. The research presented here is part of P. Nikova’s Ph.D.
dissertation topic enrolled with ordinance N◦17/19.01.2024 at IBER-BAS.
Conflicts of Interest: The authors declare no conflicts of interest.
References
1.
Patterson, B.; Ramírez-Chaves, H.; Vilela, J.; Soares, A.; Grewe, F. On the Nomenclature of the American Clade of Weasels
(Carnivora: Mustelidae). J. Anim. Divers. 2021,3, 1–8. [CrossRef]
2.
Nentwig, W.; Bacher, S.; Kumschick, S.; Pyšek, P.; Vilà, M. More than “100 Worst” Alien Species in Europe. Biol. Invasions 2018,20,
1611–1621. [CrossRef]
3.
Petrosyan, V.; Osipov, F.; Feniova, I.; Dergunova, N.; Warshavsky, A.; Khlyap, L.; Dzialowski, A. The TOP-100 Most Dangerous
Invasive Alien Species in Northern Eurasia: Invasion Trends and Species Distribution Modelling. NeoBiota 2023,82, 23–56.
[CrossRef]
4.
Ben-David, M.; Hanley, T.A.; Klein, D.R.; Schell, D.M. Seasonal Changes in Diets of Coastal and Riverine Mink: The Role of
Spawning Pacific Salmon. Can. J. Zool. 1997,75, 803–811. [CrossRef]
5.
Macdonald, D.W.; Harrington, L.A. The American Mink: The Triumph and Tragedy of Adaptation out of Context. N. Z. J. Zool.
2003,30, 421–441. [CrossRef]
6.
Hammershøj, M.; Pertoldi, C.; Asferg, T.; Bach Møller, T.; Bastian Kristensen, N. Danish Free-Ranging Mink Populations Consist
Mainly of Farm Animals: Evidence from Microsatellite and Stable Isotope Analyses. J. Nat. Conserv. 2005,13, 267–274. [CrossRef]
7.
Bonesi, L.; Palazon, S. The American Mink in Europe: Status, Impacts, and Control. Biol. Conserv. 2007,134, 470–483. [CrossRef]
8.
Genovesi, P.; Bacher, S.; Kobelt, M.; Pascal, M.; Scalera, R. Alien Mammals of Europe. In Handbook of Alien Species in Europe;
Springer: Dordrecht, The Netherlands, 2008; pp. 119–128.
9.
Vilà, M.; Basnou, C.; Pyšek, P.; Josefsson, M.; Genovesi, P.; Gollasch, S.; Nentwig, W.; Olenin, S.; Roques, A.; Roy, D.B.; et al. How
Well Do We Understand the Impacts of Alien Species on Ecosystem Services? A Pan-European, Cross-Taxa Assessment. Front.
Ecol. Environ. 2010,8, 135–144. [CrossRef]
10. Palazón, S.; Roy, S. Neovison vison (American Mink). CABI Compendium 2014. [CrossRef]
11.
Tedeschi, L.; Biancolini, D.; Capinha, C.; Rondinini, C.; Essl, F. Introduction, Spread, and Impacts of Invasive Alien Mammal
Species in Europe. Mammal Rev. 2022,52, 252–266. [CrossRef]
12.
Vada, R.; Illanas, S.; Acevedo, P.; Adriaens, T.; Apollonio, M.; Belova, O.; Blanco-Aguiar, J.A.; Csányi, S.; Body, G.; Fernández-De-
Mera, I.G.; et al. Feral American Mink Neogale vison Continues to Expand Its European Range: Time to Harmonise Population
Monitoring and Coordinate Control. Mammal Rev. 2023,53, 158–176. [CrossRef]
13.
Larsen, H.D.; Fonager, J.; Lomholt, F.K.; Dalby, T.; Benedetti, G.; Kristensen, B.; Urth, T.R.; Rasmussen, M.; Lassaunière, R.;
Rasmussen, T.B.; et al. Preliminary Report of an Outbreak of SARS-CoV-2 in Mink and Mink Farmers Associated with Community
Spread, Denmark, June to November 2020. Eurosurveillance 2021,26, 2100009. [CrossRef]
14.
Oude Munnink, B.B.; Sikkema, R.S.; Nieuwenhuijse, D.F.; Molenaar, R.J.; Munger, E.; Molenkamp, R.; van der Spek, A.; Tolsma, P.;
Rietveld, A.; Brouwer, M.; et al. Transmission of SARS-CoV-2 on Mink Farms between Humans and Mink and Back to Humans.
Science 2021,371, 172–177. [CrossRef]
15.
Aguiló-Gisbert, J.; Padilla-Blanco, M.; Lizana, V.; Maiques, E.; Muñoz-Baquero, M.; Chillida-Martínez, E.; Cardells, J.; Rubio-
Guerri, C. First Description of SARS-CoV-2 Infection in Two Feral American Mink (Neovison vison) Caught in the Wild. Animals
2021,11, 1422. [CrossRef] [PubMed]
Ecologies 2024,5623
16.
Fenollar, F.; Mediannikov, O.; Maurin, M.; Devaux, C.; Colson, P.; Levasseur, A.; Fournier, P.-E.; Raoult, D. Mink, SARS-CoV-2,
and the Human-Animal Interface. Front. Microbiol. 2021,12, 663815. [CrossRef] [PubMed]
17.
Hammer, A.S.; Quaade, M.L.; Rasmussen, T.B.; Fonager, J.; Rasmussen, M.; Mundbjerg, K.; Lohse, L.; Strandbygaard, B.; Jørgensen,
C.S.; Alfaro-Núñez, A.; et al. SARS-CoV-2 Transmission between Mink (Neovison vison) and Humans, Denmark. Emerg. Infect. Dis.
2021,27, 547–551. [CrossRef]
18.
Azami-Conesa, I.; Sansano-Maestre, J.; Martínez-Díaz, R.A.; Gómez-Muñoz, M.T. Invasive Species as Hosts of Zoonotic Infections:
The Case of American Mink (Neovison vison) and Leishmania Infantum. Microorganisms 2021,9, 1531. [CrossRef] [PubMed]
19.
Agüero, M.; Monne, I.; Sánchez, A.; Zecchin, B.; Fusaro, A.; Ruano, M.J.; Del Valle Arrojo, M.; Fernández-Antonio, R.; Souto,
A.M.; Tordable, P.; et al. Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in Farmed Minks, Spain, October 2022.
Eurosurveillance 2023,28, 2300001. [CrossRef]
20.
Ribas, M.P.; Almería, S.; Fernández-Aguilar, X.; De Pedro, G.; Lizarraga, P.; Alarcia-Alejos, O.; Molina-López, R.; Obón, E.;
Gholipour, H.; Temiño, C.; et al. Tracking Toxoplasma Gondii in Freshwater Ecosystems: Interaction with the Invasive American
Mink (Neovison vison) in Spain. Parasitol. Res. 2018,117, 2275–2281. [CrossRef]
21.
Zalewski, A.; Virtanen, J.M.E.; Brzezi´nski, M.; Kołodziej-Soboci´nska, M.; Jankow, W.; Sironen, T. Aleutian Mink Disease: Spatio-
Temporal Variation of Prevalence and Influence on the Feral American Mink. Transbound. Emerg. Dis. 2021,68, 2556–2570.
[CrossRef]
22.
Mañas, S.; Ceña, J.C.; Ruiz-Olmo, J.; Palazón, S.; Domingo, M.; Wolfinbarger, J.B.; Bloom, M.E. Aleutian Mink Disease Parvovirus
in Wild Riparian Carnivores in Spain. J. Wildl. Dis. 2001,37, 138–144. [CrossRef] [PubMed]
23.
Peacock, T.P.; Barclay, W.S. Mink Farming Poses Risks for Future Viral Pandemics. Proc. Natl. Acad. Sci. USA 2023,120,
e2303408120. [CrossRef] [PubMed]
24.
Kauhala, K. Distributional History of the American Mink (Mustela vison) in Finland with Special Reference to the Trends in Otter
(Lutra Lutra) Populations. Ann. Zool. Fenn. 1996,33, 283–291.
25.
Ruiz-Olmo, J.; Palazón, S.; Bueno, F.; Bravo, C.; Munilla, I.; Moreno, R. Distribution, Status and the Colonization Process of the
American Mink (Mustela vison) in Spain. J. Wildl. Res. 1997,2, 30–36.
26.
Bonesi, L.; Chanin, P.; Macdonald, D.W. Competition between Eurasian Otter Lutra lutra and American Mink Mustela vison Probed
by Niche Shift. Oikos 2004,106, 19–26. [CrossRef]
27.
Sidorovich, V.; Kruuk, H.; Macdonald, D.W. Body Size, and Interactions between European and American Mink (Mustela lutreola
and M. vison) in Eastern Europe. J. Zool. 1999,248, 521–527. [CrossRef]
28.
Melero, Y.; Palazón, S.; Bonesi, L.; Gosàlbez, J. Feeding Habits of Three Sympatric Mammals in NE Spain: The American Mink,
the Spotted Genet, and the Eurasian Otter. Acta Theriol. 2008,53, 263–273. [CrossRef]
29.
Schüttler, E.; Cárcamo, J.; Rozzi, R. Diet of the American Mink Mustela vison and Its Potential Impact on the Native Fauna of
Navarino Island, Cape Horn Biosphere Reserve, Chile. Rev. Chil. Hist. Nat. 2008,81, 585–598. [CrossRef]
30.
Krawczyk, A.J.; Bogdziewicz, M.; Czy˙
z, M.J. Diet of the American Mink Neovison vison in an Agricultural Landscape in Western
Poland. Folia Zool. 2013,62, 304–310. [CrossRef]
31.
Kiseleva, N.V. Variation in the Diet of American Mink, Neovison vison, in Water Bodies of the Ilmen State Reserve. Russ. J. Ecol.
2014,45, 322–324. [CrossRef]
32.
Zschille, J.; Stier, N.; Roth, M.; Mayer, R. Feeding Habits of Invasive American Mink (Neovison vison) in Northern Germany—
Potential Implications for Fishery and Waterfowl. Acta Theriol. 2013,59, 25–34. [CrossRef]
33.
Ferreras, P.; Macdonald, D.W. The Impact of American Mink Mustela vison on Water Birds in the Upper Thames. J. Appl. Ecol.
1999,36, 701–708. [CrossRef]
34. Dragoev, P. Enrichment of Hunting Fauna in Bulgaria; Zemizdat: Sofia, Bulgaria, 1978.
35.
Koshev, Y.S. Occurrence of the American Mink Neovison vison (Schreber, 1777) (Carnivora: Mustelidae) in Bulgaria. Acta Zool.
Bulg. 2019,71, 417–425.
36.
Koshev, Y.S.; Nedyalkov, N.P.; Raykov, I.A. Range Expansion of Three Invasive Alien Mammals in Bulgaria. Rus. J. Theriol. 2022,
21, 53–62. [CrossRef]
37.
Bulgarian Food Safety Agency. Register of Facilities Intended for Rearing Furry and Feathered Game in the Republic of Bulgaria.
Available online: https://web.archive.org/web/20230706202720/https://bfsa.egov.bg/wps/wcm/connect/bfsa.egov.bg1
9113/20287b38-52b1-4a70-9a3b-b85ffb4ee4c2/9+-+Register_wild+animals+-+2021.10.05.xlsx?MOD=AJPERES&CONVERT_
TO=url&CACHEID=ROOTWORKSPACE.Z18_PPGAHG8009DK40685BSRP0Q203-20287b38-52b1-4a70-9a3b-b85ffb4ee4c2
-ozZzR0V (accessed on 13 March 2024).
38. Finnish Fur Breeders’ Association. FiFur Statistics 2023; Finnish Fur Breeders’ Association: Vantaa, Finland, 2023.
39.
MOEW. Minister Borislav Sandov Banned the Import and Breeding of Mink Due to Their Impacts on Biodiversity.
Available online: https://web.archive.org/web/20240129202551/https:/www.moew.government.bg/bg/ministur-borislav-
sandov-zabrani-vnosa-i-razvujdaneto-na-norki-zaradi-vredata-vurhu-bioraznoobrazieto/ (accessed on 11 February 2024).
40.
State Gazette Ordinance
№
RD-449 from 31st of May 2022. In Darzhaven Vestnik; Republic of Bulgaria: Sofia, Bulgaira, 2022;
pp. 30–33.
41.
Court Decision
№
7624, Sofia, 05.08.2022 on Administrative Case
№
6852/2022. Available online: https://info-adc.justice.bg/
courts/portal/edis.nsf/e_act.xsp?id=1971930&code=vas&guid=2072767410&q=%D0%BD%D0%BE%D1%80%D0%BA%D0
%B8 (accessed on 11 February 2024).
Ecologies 2024,5624
42.
Iordan, F.; Lapini, L.; Pavanello, M.; Polednik, L.; Rieppi, C. Evidence for Naturalization of the American Mink (Neovison vison) in
Friuli Venezia Giulia, NE Italy. Mammalia 2017,81, 91–94. [CrossRef]
43. Larivière, S. Mustela vison.Mamm. Species 1999, 1–9. [CrossRef]
44.
Ahlers, A.A.; Cotner, L.A.; Wolff, P.J.; Mitchell, M.A.; Heske, E.J.; Schooley, R.L. Summer Precipitation Predicts Spatial Distribu-
tions of Semiaquatic Mammals. PLoS ONE 2015,10, e0135036. [CrossRef]
45.
Fuller, A.K.; Sutherland, C.S.; Royle, J.A.; Hare, M.P. Estimating Population Density and Connectivity of American Mink Using
Spatial Capture–Recapture. Ecol. Appl. 2016,26, 1125–1135. [CrossRef]
46.
Zielinski, W.J. Circadian Rhythms of Small Carnivores and the Effect of Restricted Feeding on Daily Activity. Physiol. Behav. 1986,
38, 613–620. [CrossRef]
47.
Sidorovich, V.E. Seasonal Variation in the Feeding Habits of Riparian Mustelids in River Valleys of NE Belarus. Acta Theriol. 2000,
45, 233–242. [CrossRef]
48.
Spasov, N. European mink Mustela lutreola (Linnaeus, 1761). In Red Data Book of the Republic of Bulgaria; Golemanski, V., Peev, D.,
Chipev, N., Beron, P., Biserkov, V., Eds.; Bulgarian Academy of Sciences and Ministry of Environment and Water: Sofia, Bulgaria,
2015; Volume 2, p. 34. ISBN 978-954-9746-19-8.
49.
Lange, P.N.A.M.J.G.; Lelieveld, G.; De Knegt, H.J. Diet Composition of the Golden Jackal Canis Aureus in South-east Europe—A
Review. Mammal Rev. 2021,51, 207–213. [CrossRef]
50.
Chao, A.; Gotelli, N.J.; Hsieh, T.C.; Sander, E.L.; Ma, K.H.; Colwell, R.K.; Ellison, A.M. Rarefaction and Extrapolation with Hill
Numbers: A Framework for Sampling and Estimation in Species Diversity Studies. Ecol. Monogr. 2014,84, 45–67. [CrossRef]
51.
Hsieh, T.C.; Ma, K.H.; Chao, A. iNEXT: An R Package for Rarefaction and Extrapolation of Species Diversity (Hill Numbers).
Method. Ecol. Evol. 2016,7, 1451–1456. [CrossRef]
52. R Core Team. R: A Language and Environment for Statistical Computing; R Foundation for Statistical Computing: Vienna, Austria, 2021.
53. RStudio Team. RStudio: Integrated Development Environment for R; RStudio, PBC: Boston, MA, USA, 2020.
54.
QGIS Development Team QGIS Geographic Information System. Available online: http://qgis.osgeo.org (accessed on
7 November 2024).
55. Wickham, H. Ggplot2: Elegant Graphics for Data Analysis; Springer: New York, NY, USA, 2016; ISBN 978-3-319-24277-4.
56.
Wickham, H.; Hester, J.; Chang, W.; Bryan, J. Devtools: Tools to Make Developing R Packages Easier. Available online:
https://github.com/r-lib/devtools (accessed on 1 November 2024).
57.
Kassambara, A. ggpubr: “ggplot2” Based Publication Ready Plots. Available online: https://rpkgs.datanovia.com/ggpubr/
(accessed on 7 November 2024).
58.
FC, M.; Davis, T.L. ggpattern: “ggplot2” Pattern Geoms. Available online: https://cran.r-project.org/package=ggpattern
(accessed on 7 November 2024).
59.
Wilke, C.O. Cowplot: Streamlined Plot Theme and Plot Annotations for “Ggplot2”. Available online: https://wilkelab.org/
cowplot/ (accessed on 7 November 2024).
60.
Peshev, T.; Peshev, D.; Popov, V. Fauna of Bulgaria Vol. 27 Mammalia, Fauna Bulgarica, 1st ed.; Marin Drinov: Sofia, Bulgaria, 2004;
Volume 27, ISBN 954-430-860-1.
61.
Hulme, P.E.; Bacher, S.; Kenis, M.; Klotz, S.; Kühn, I.; Minchin, D.; Nentwig, W.; Olenin, S.; Panov, V.; Pergl, J.; et al. Grasping at
the Routes of Biological Invasions: A Framework for Integrating Pathways into Policy. J. Appl. Ecol. 2008,45, 403–414. [CrossRef]
62.
Convention on Biological Diversity. Pathways of Introduction of Invasive Species, Their Prioritization and Management. In
UNEP/CBD/SBSTTA/18/9/Add. 1. Montréal: Secretariat of the Convention on Biological Diversity; Convention on Biological Diversity:
Montreal, QC, Canada, 2014.
63.
Yamaguchi, N.; Macdonald, D.W. The Burden of Co-Occupancy: Intraspecific Resource Competition and Spacing Patters in
American Mink, Mustela vison.J. Mammal. 2003,84, 1341–1355. [CrossRef]
64. Dunstone, N. The Mink; Poyser Natural History; Poyser: London, UK, 1993; ISBN 978-0-85661-080-6.
65.
Bartoszewicz, M.; Zalewski, A. American Mink, Mustela vison Diet and Predation on Waterfowl in the Slonsk Reserve, Western
Poland. Folia Zool. 2003,52, 225–238.
66. Mitchell, J.L. Mink Movements and Populations on a Montana River. J. Wildl. Manag. 1961,25, 48–54. [CrossRef]
67. Gerell, R. Food Selection in Relation to Habitat in Mink (Mustela vison Schreber) in Sweden. Oikos 1967,18, 233–246. [CrossRef]
68.
Gerell, R. Home Ranges and Movements of the Mink Mustela vison Shreber in Southern Sweden. Oikos 1970,21, 160–173.
[CrossRef]
69.
Iordan, F.; Rushton, S.P.; Macdonald, D.W.; Bonesi, L. Predicting the Spread of Feral Populations of the American Mink in Italy: Is
It Too Late for Eradication? Biol. Invasions 2012,14, 1895–1908. [CrossRef]
70.
Harrington, L.A.; Birks, J.; Chanin, P.; Tansley, D. Current Status of American Mink Neovison vison in Great Britain: A Review of
the Evidence for a Population Decline. Mammal Rev. 2020,50, 157–169. [CrossRef]
71. Bakaloudis, D.; Thoma, C.; Makridou, K.; Kotsonas, E. Occupancy Dynamics of Free Ranging American Mink (Neogale vison) in
Greece. Sci. Rep. 2024,14, 9973. [CrossRef] [PubMed]
72.
Brzezi´nski, M.; ˙
Zmihorski, M.; Zarzycka, A.; Zalewski, A. Expansion and Population Dynamics of a Non-Native Invasive Species:
The 40-Year History of American Mink Colonisation of Poland. Biol. Invasions 2019,21, 531–545. [CrossRef]
73.
García, K.; Palazón, S.; Gosálbez, J.; Melero, Y. Detection Probabilities of the Native Eurasian Otter and the Invasive American
Mink Are Independent of Their Co-Occurrence. Mammal Res. 2020,65, 459–467. [CrossRef]
Ecologies 2024,5625
74.
Harlow, H.J. Trade-Offs Associated with the Size and Shape of American Marten. In Martens, Sables and Fishers, Biology and
Conservation; Buskirk, S.W., Harested, A.S., Raphael, M.G., Powell, R.A., Eds.; Cornell Univeristy Press: London, UK, 1994;
pp. 391–403.
75.
Zuberogoitia, I.; Zabala, J.; Martínez, J.A. Diurnal Activity and Observations of the Hunting and Ranging Behaviour of the
American Mink (Mustela vison)/ActivitéDiurne et Observations Du Comportement de Chasse et Habitat Du Vison d’Amerique
(Mustela vison). Mammalia 2006,70, 310–312. [CrossRef]
76. Gerell, R. Activity Patterns of the Mink Mustela vison Schreber in Southern Sweden. Oikos 1969,20, 451–460. [CrossRef]
77.
Yamaguchi, N.; Rushton, S.; Macdonald, D.W. Habitat Preferences of Feral American Mink in the Upper Thames. J. Mammal.
2003,84, 1356–1373. [CrossRef]
78.
García, P.; Isabel, M.; Arévalo, V. Diurnal Activity of the American Mink (Neovison vison) in Central Spain. Hystrix 2009,20, 61–68.
[CrossRef]
79.
Niemimaa, J. Activity Patterns and Home Ranges of the American Mink Mustela vison in the Finnish Outer Archipelago. Ann.
Zool. Fenn. 1995,32, 117–121.
80.
Poláˇcková, I.; Šerá, B.; Jureˇcek, R.; Pavliˇcková, K. The Daily and Seasonal Behaviour of the American Mink and the Coypu, Two
Invasive Species from the Záhorie PLA (Slovakia). Acta Ethol. 2022,25, 115–123. [CrossRef]
81.
Adamopoulou, C.; Legakis, A. First Account on the Occurrence of Selected Invasive Alien Vertebrates in Greece. BioInvasions Rec.
2016,5, 189–196. [CrossRef]
82. Galanaki, A.; Kominos, T. The Distribution of American Mink (Neovison vison) in Greece. Mammalia 2021,86, 57–65. [CrossRef]
83.
Hegyeli, Z.; Kecskés, A. The Occurrence of Wild-Living American Mink Neovison vison in Transylvania, Romania. Small Carniv.
Conserv. 2014,51, 23–28.
84.
Ionescu, D.T.; Hodor, C.; Drugă, M.; Drugă, M. Recent Occurrence of the American Mink (Neovison vison) in the Central Romania.
In Proceedings of the 8th Edition of the Biennial International Symposium Forest And Sustainable Development, Bra
s
,
ov, Romania,
5 October 2018; pp. 25–32.
85.
Blackburn, T.M.; Pyšek, P.; Bacher, S.; Carlton, J.T.; Duncan, R.P.; Jarošík, V.; Wilson, J.R.U.; Richardson, D.M. A Proposed Unified
Framework for Biological Invasions. Trends Ecol. Evol. 2011,26, 333–339. [CrossRef]
86. Colautti, R.; MacIsaac, H. A Neutral Terminology to Define ‘Invasive’ Species. Divers. Distrib. 2004,10, 135–141. [CrossRef]
87. Dekker, J.J.A.; Hofmeester, T.R. The Status of the American Mink (Neovison vison) in the Netherlands. Lutra 2014,57, 5–15.
88.
Pagh, S.; Pertoldi, C.; Petersen, H.H.; Jensen, T.H.; Hansen, M.S.; Madsen, S.; Kraft, D.C.E.; Iversen, N.; Roslev, P.; Chriel, M.
Methods for the Identification of Farm Escapees in Feral Mink (Neovison vison) Populations. PLoS ONE 2019,14, e0224559.
[CrossRef] [PubMed]
89.
Brzezi´nski, M.; ˙
Zurowski, W. Spring Diet of the American Mink Mustela vison in the Mazurian and Brodnica Lakelands, Northern
Poland. Acta Theriol. 1992,37, 193–198. [CrossRef]
90.
Halliwell, E.C.; Macdonald, D.W. American Mink Mustela vison in the Upper Thames Catchment: Relationship with Selected Prey
Species and Den Availability. Biol. Conserv. 1996,76, 51–56. [CrossRef]
91.
Sidorovich, V.; Macdonald, D.; Pikulik, M.M.; Kruuk, H. Individual Feeding Specialization in the European Mink, Mustela lutreola
and the American Mink, M. vison in North-Eastern Belarus. Folia Zool. 2001,50, 27–42.
92.
Nováková, M.; Koubek, P. Diet of the American Mink (Mustela vison) in the Czech Republic (Carnivora: Mustelidae). Lynx 2006,
37, 173–177.
93.
Brzezi´nski, M. Food Habits of the American Mink Mustela vison in the Mazurian Lakeland, Northeastern Poland. Mamm. Biol.
2008,73, 177–188. [CrossRef]
94.
Fischer, D.; Pavluvˇcík, P.; Sedláˇcek, F.; Šálek, M. Predation of the Alien American Mink, Mustela vison on Native Crayfish in
Middle-Sized Streams in Central and Western Bohemia. Folia Zool. 2009,58, 45–56.
95.
Strachan, C.; Jefferies, D.J.; Barreto, G.R.; Macdonald, D.W.; Strachan, R. The Rapid Impact of Resident American Mink on
Water Voles: Case Studies in Lowland England. In Behaviour and Ecology of Riparian Mammals; Dunstone, N., Gorman, M.L.,
Eds.; Symposia of the Zoological Society of London; Cambridge University Press: Cambridge, UK, 1998; pp. 339–358. ISBN
978-0-521-63101-3.
96.
Barreto, G.R.; Rushton, S.P.; Strachan, R.; Macdonald, D.W. The Role of Habitat and Mink Predation in Determining the Status
and Distribution of Water Voles in England. Anim. Consevr 1998,1, 129–137. [CrossRef]
97.
MacDonald, D.W.; Sidorovich, V.E.; Anisomova, E.I.; Sidorovich, N.V.; Johnson, P.J. The Impact of American Mink Mustela vison
and European Mink Mustela lutreola on Water Voles Arvicola Terrestris in Belarus. Ecography 2002,25, 295–302. [CrossRef]
98. Popov, V.; Sedefchev, A. Mammals in Bulgaria, 1st ed.; Geosoft: Sofia, Bulgaria, 2003.
99.
Sidorovich, V.E. (Ed.) Spatial structure of mustelid populations and assembly as an environment function. In Mustelids in Belarus;
Zolotoy Uley: Minsk, Russia, 1997.
100.
Bonesi, L.; MacDonald, D.W. Impact of Released Eurasian Otters on a Population of American Mink: A Test Using an Experimental
Approach. Oikos 2004,106, 9–18. [CrossRef]
101.
Maran, T.; Kruuk, H.; Macdonald, D.; Polma, M. Diet of Two Species of Mink in Estonia: Displacement of Mustela lutreola by M.
Vison.J. Zool. 1998,245, 218–222. [CrossRef]
102.
Sidorovich, V.E.; Polozov, A.G.; Zalewski, A. Food Niche Variation of European and American Mink during the American Mink
Invasion in North-Eastern Belarus. Biol. Invasions 2010,12, 2207–2217. [CrossRef]
Ecologies 2024,5626
103.
Maran, T.; Henttonen, H. Why Is the European Mink (Mustela lutreola) Disappearing?—A Review of the Process and Hypotheses.
Ann. Zool. Fenn. 1995,32, 47–54.
104.
Põdra, M.; Gómez, A.; Palazón, S. Do American Mink Kill European Mink? Cautionary Message for Future Recovery Efforts. Eur.
J. Wildl. Res. 2013,59, 431–440. [CrossRef]
105.
Knuuttila, A.; Aaltonen, K.; Virtala, A.-M.K.; Henttonen, H.; Isomursu, M.; Leimann, A.; Maran, T.; Saarma, U.; Timonen, P.;
Vapalahti, O.; et al. Aleutian Mink Disease Virus in Free-Ranging Mustelids in Finland—A Cross-Sectional Epidemiological and
Phylogenetic Study. J. Gen. Virol. 2015,96, 1423–1435. [CrossRef]
106.
Fournier-Chambrillon, C.; Aasted, B.; Perrot, A.; Pontier, D.; Sauvage, F.; Artois, M.; Cassiède, J.-M.; Chauby, X.; Molin, A.; Simon,
C.; et al. Antibodies to Aleutian Mink Disease Parvovirus in Free-Ranging European Mink (Mustela lutreola) and Other Small
Carnivores from Southwestern France. J. Wildl. Dis. 2004,40, 394–402. [CrossRef] [PubMed]
107.
Yamaguchi, N.; Macdonald, D.W. Detection of Aleutian Disease Antibodies in Feral American Mink in Southern England. Vet.
Rec. 2001,149, 485–488. [CrossRef] [PubMed]
108.
Golemanski, V.; Peev, D.; Chipev, N.; Beron, P.; Biserkov, V. Red Data Book of the Republic of Bulgaria. Animals, 1st ed.; Bulgarian
Academy of Sciences and Ministry of Environment and Water: Sofia, Bulgaria, 2015.
109. FAWC. Farm Animal Welfare in Great Britain: Past, Present and Future; Farm Animal Welfare Council: London, UK, 2009.
110. Pickett, H.; Harris, S. The Case Against Fur Factory Farming, 1st ed.; Respect for Animals: Nottingham, UK, 2015.
111.
National Assembly of the Republic of Bulgaria. Bill to Amend and Supplement the Law on Veterinary Medicine. Available online:
https://www.parliament.bg/bg/bills/ID/165115 (accessed on 18 March 2024).
112. Zuberogoitia, I. Facing Extinction, Last Call for the European Mink. Ann. Rev. Resear 2018,2, 555581. [CrossRef]
113. Rojek, B. European Citizens’ Initiative: “Fur Free Europe”; European Parliament: Brussels, Belgium, 2023.
114.
Reynolds, J.C.; Short, M.J.; Leigh, R.J. Development of Population Control Strategies for Mink Mustela vison, Using Floating Rafts
as Monitors and Trap Sites. Biol. Conserv. 2004,120, 533–543. [CrossRef]
115.
Fraser, E.J.; Harrington, L.A.; Macdonald, D.W.; Lambin, X. Control of an Invasive Species: The American Mink in Great Britain.
In Biology and Conservation of Musteloids; Macdonald, D.W., Newman, C., Harrington, L.A., Eds.; Oxford University Press: Oxford,
UK, 2017; pp. 357–369, ISBN 978-0-19-875980-5.
116.
Stefansson, R.A.; von Schmalensee, M.; Skorupski, J. A Tale of Conquest and Crisis: Invasion History and Status of the American
Mink (Neovison vison) in Iceland. Acta Biol. 2016,23, 87–100. [CrossRef]
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual
author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to
people or property resulting from any ideas, methods, instructions or products referred to in the content.
