Possible reasons for decline European mink

1 possible reasons decline

1.1 habitat loss
1.2 overhunting
1.3 decline of crayfish
1.4 competition american mink , disease
1.5 hybridisation , competition european polecat
1.6 predation

possible reasons decline
habitat loss

habitat-related declines of european mink numbers may have started during little ice age, further aggravated human activity. european mink more dependent on wetland habitats american species, decline in central europe, estonia, finland, russia, moldova , ukraine has been linked drainage of small rivers. in mid-19th-century germany, example, european mink populations declined in decade due expanded land drainage. although land improvement , river dredging resulted in population decreases , fragmentation, in areas still maintain suitable river ecosystems, such poland, hungary, former czechoslovakia, finland , russia, decline preceded change in wetland habitats, , may have been caused extensive agricultural development.

overhunting

the european mink historically hunted extensively, particularly in russia, in districts, decline prompted temporary ban on mink hunting let population recover. in 20th century, 40-60,000 european minks caught annually in soviet union, record of 75,000 individuals (an estimate exceeds modern global european mink population). in finland, annual mink catches reached 3000 specimens in 1920s. in romania, 10,000 minks caught annually around 1960. however, reason alone cannot account decline in areas hunting less intense, such in germany.

decline of crayfish

the decline of european crayfish has been proposed factor in drop in mink numbers, minks notably absent in eastern side of urals, crayfish absent. decline in mink numbers has been linked destruction of crayfish in finland during 1920s-1940s, when crustaceans infected crayfish plague. failure of european mink expand west scandinavia coincides gap in crayfish distribution.

competition american mink , disease

the american mink introduced , released in europe during 1920s-1930s. american mink less dependent on wetland habitats european mink , 20-40% larger. impact of feral american minks on european mink populations has been explained through competitive exclusion principle , because american mink reproduces month earlier european species, , matings between male american minks , female european minks result in embryos being reabsorbed. thus, female european minks impregnated male american minks unable reproduce conspecifics. disease spread american mink can account decline. though presence of american mink has coincided decline of european mink numbers in belarus , estonia, decline of european mink in areas preceded introduction of american mink many years, , there areas in russia american species absent, though european mink populations in these regions still declining.

diseases spread american mink can account decline. twenty-seven helminth species recorded infest european mink, consisting of 14 trematodes, 2 cestodes , 11 nematodes. mink vulnerable pulmonary filariasis, krenzomatiasis , skrjabingylosis. in leningrad , pskov oblasts, 77.1% of european minks found infected skrjabingylosis.

hybridisation , competition european polecat

in 20th century, northern europe underwent warm climatic period coincided expansion of range of european polecat. european mink possibly gradually absorbed polecat due hybridisation. also, competition polecat has increased, due landscape change favouring polecat. there 1 record of polecat attacking mink , dragging burrow.

polecat-mink hybrids termed khor -tumak furriers , khonorik fanciers. such hybridisation rare in wild, , typically occurs european minks declining. polecat-mink hybrid has poorly defined facial mask, yellow fur on ears, grey-yellow underfur , long, dark brown guard hairs. large, males attain peak sizes known european polecats (weighing 1,120–1,746 g (2.469–3.849 lb) , measuring 41–47 cm (16–19 in) in length), , females larger female european minks (weighing 742 g (1.636 lb) , measuring 37 cm (15 in) in length). majority of polecat-mink hybrids have skulls bearing greater similarities of polecats minks. hybrids can swim minks , burrow food polecats. difficult tame , breed, males sterile, though females fertile. first captive polecat-mink hybrid created in 1978 soviet zoologist dr. dmitry ternovsky of novosibirsk. bred fur (which more valuable of either parent species), breeding of these hybrids declined european mink populations decreased. studies on behavioural ecology of free-ranging polecat-mink hybrids in upper reaches of lovat river indicate hybrids stray aquatic habitats more readily pure minks, , tolerate both parent species entering territories, though hybrid s larger size (especially male s) may deter intrusion. during summer period, diet of wild polecat-mink hybrids more similar of mink polecat, feed predominantly on frogs. during winter, diets overlap more of polecats, , eat larger proportion of rodents in summer, though still rely heavily on frogs , scavenge ungulate carcasses polecat does.

predation

predators of european mink include european polecat, american mink, golden eagle, large owls , red fox. red fox numbers have increased in areas wolf , eurasian lynx have been extirpated, areas modern forestry practised. red foxes known prey on mustelids, excessive fox predation on european mink possible factor, though improbable have been factor in finland, fox numbers low during 20th century.