The North American mink - Mustela vison
Helle Ruth Isaksen, veterinary student, 1st year
The
North American mink has been introduced to many countries, among other
countries; Norway, for commercial fur production. Mink who have escaped
death at Norwegian fur farms have found their place in our ecosystem and
have resulted in large breeding populations in the wild.
After reading a report about effects of feral mink removal on birds, especially
seabirds, I found this subject interesting and wanted to see how the population
of mink is in Norway. Is the mink a problem in Norway? What can we do
to control the population of mink? I want to see if the minks can have
a negative impact on local wildlife and domestic stock.
The North American mink, Mustela vison, is a member ofthe family Mustelidae. This carnivore has an elongated body approximately 65 cm long with the tail, and it has short limbs. The mink has the size of a small housecat, the male being heavier then the female. Their weight is 0,5-1 kg. Wild native American mink are uniformly dark brown with a light spot under the chin, but breeding in fur farms has resulted in a wide range of fur colours, and consequently escaped feral mink may vary in colour ffom white, grey or fawn through to black. The fur does not let water through, this is good since the mink live most in the water. They are great swimmers and divers. The mink also live on land. They don't have a natural enemy, and no of the Norwegian carnivores manage to catch the mirik because oftheir intelligence and enormous capability to run fast.
American mink is a semi-aquatic, generalist predators and its main food
consist of fish, birds( eggs, nestling as well as adults), small mammals
and amphibian. (http://bio.univet.hu/SAL VE/student- essay/libr/mink -
baltic.pdt) They are very adaptable and can exploit a wide range of foods.
They are also known for raiding poultry houses. I will concentrate about
their meals when it is about birds, mainly wading birds, and fish. This
is because I know that the mink could be a problem in these area.
In the northern hemisphere the mating season is in March, during which
both sexes may mate with several partners. The female gives birth to a
maximum of six kits during April and May, although a much smaller number
than this are likely to survive to dispersal in late July. (http://www.ccs.st-and.ac.uk/mink.php)
The species was introduced into many countries throughout the world,
one of them Norway, from about the 1920s, as an animal farmed for its
fur. Many animals escaped, and started to breed in the wild. The mink
adjusted itself to the nature in Norway very fast, mainly because the
norwegian nature is almost equal to the one in North-America. Under the
second worldwar many of the minks were released because the farmer didn't
have enough food to feed themselves and the animals. In more recent years,
large numbers of mink have been deliberately released from farms by animal
rights activists.
The mink stays in the near of seas, watercourses and along the coast.
They live in caves below trees, in screes and beneath heaps of grasses.
They kill brooding wadingbirds and takes their eggs. They kills more preys
than they eat at once, and their hiding the rests till they get hungry
again.
As mink are generalist predators they may negatively affect a prey species
even if that species doesn't form a large or important part oftheir diet.
It also means that the decreasing of a prey species due to mink predation
will not necessarily result in a decrease in the size of the mink population
as they are able to switch to alternative prey (http://www.ccs.st-and.ac.
uk/mink. php ).
The mink predation at seabird colonies has been studied much in Norway,
and we can see that spreading of minks has resulted in decreasing in many
populations of seabirds.
One of the reasons why this decreasing is so high, is because of how the
mink is collecting it's food. Usually the animals are hunting because
they feel a hunger, then they collect what they need to fill their need.
The mink is collecting much more than itself, and their kids, manages
to eat, so-called overhunting. For example they can raid many nests in
one time, but maybe eat only 3 eggs from one nest. The mink is also a
big problem for fishfarms; they are often raiding the farms and they can
bring diseases from other fishwaters. I will tell about diseases later.
The mink is also a competitor with species we have naturally in the norwegian fauna, for example otter (Lutra lutra). They have the same habitat, live in the near of water and eating mainly same food, fish, especially in the winter. This invading species may therefore pose a risk to the otter through competition for food and territories. Norwegian researchers are not sure if this can result in habitat loss for some of the species, or if the overhunting can lead to lacking of food for their arrival.
There is also evidence that mink could account for a large proportion
of salmonid mortality in some river systems and fishfarms.
The Aleutian mink disease parvovirus (ADV) is commonly found in American mink on fur farms. This disease is highly persistent in the environment and can be spread either from mother to offspring, or via contact with urine, faeces or saliva. In addition to direct mortality, infection with ADV can cause decreases in fertility and spontaneous abortions. It is possible that farms may act as a source of the disease but more work is required to determine the prevalence ofthe disease in the wild.(http://www.ccs.st-and.ac.uk/mink.php)
It is now clear that populations of some species do suffer with the introduction of American mink into the local fauna, especially wading birds and fish. There are several potential problems associated with mink for native wildlife. For native wildlife, mink may be considered a threat as predators, competitors or as vectors of diseases. The large population of mink are damaging parts of the norwegian fauna.
In researches on small islands in the Baltic sea it is proofed that mink removal increases breeding densities of many birds species in that habitat. This is why norwegian hunters get rewards for killing the mink. If we weren't allowed to hunt on them, I think maybe some species would have died out, especially some of the wadingbirds.
Sources:
Internet
http://bio.univet.hu/SAL VE/student essay/libr/mink baltic.pdf
http://www.sabima.no/vatmark/pattedyr.htm
http://www.hordaland-f.kommune.no/sti/Natforv%202b/MINK.htm->siekk http://www.nocompromise.org/news/norway.html http://www.ccs.st-and.ac. uk/mink. php
Books
-Gyldendal store leksikon, Oslo 1972
-Dyr og vekster i Norge(animals and plants in Norway), Ba1je Lafving 1986,
NSK forlaget 1990
Helle Ruth Isaksen, l.year wildlife ecology,2004