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American Mink

American Mink © Kevin O'Hara

The Mink Neovision vison is a medium sized, semi-aquatic carnivore native to North America. It belongs to the Mustelidae family. Mink are normally dark chocolate brown in colour usually with a white chin patch and white patches on the belly, chest and groin. Colours can vary due to breeding from mutated individuals on fur farms. In Northumbria Mink colours include chocolate brown and almost black but paler forms have also been observed by the author and also by Johnston (1974).

The introduction of the American Mink into the UK for fur farming began in 1929 and individuals have been escaping into the wild since this time (Thompson, 1968). By the 1970s, feral Mink had successfully established themselves along river catchments in virtually all counties particularly Hampshire, Wiltshire, Gloucestershire, Lancashire and Yorkshire (Dunstone, 1993) and have been breeding in the wild since this time.

Under the Fur Farming (Prohibition) Act of 2000, England and Wales banned fur farming completely. All fur farms in England and Wales had to be closed by 1 January 2003. The last fur farm in Northumberland was Cornyhaugh Fur Farm in Ponteland which closed in 2003.

Mink appeared in Northumberland in the early 1960s when the first fur farm was established. Between 1962 and 1974 numbers of Northumberland fur farms fluctuated between two and six and Mink began to escape from this time. Johnston (1974) produced the only comprehensive, early account of wild Mink in Northumberland. The first Mink recorded in the wild escaped from a farm in Newbiggin in 1963. A few other Mink were recorded in 1965 from the same area and also from Ford and Alnwick. These escaped Mink were unlikely to have been breeding due to their scarcity and the widespread distribution of the fur farms.

The first record of breeding in Northumberland was near Bedlington on the River Blyth in 1966: this Mink was located by otter-hounds. A trapping exercise was initiated by the Ministry for Agriculture Forestry and Food on the River Blyth and between 1966 and 1967, eleven Mink were caught. Mink were also recorded along the North Tyne although no fur farms were established in this area; the first record was at Nunwick Hall with Mink prints also recorded from Wark bridge to Corbridge. A trapping exercise during the same period caught 25 Mink. Mink were first sighted on the River Coquet at Warkworth in 1967; prints were observed at Guyzance bridge, Warkworth and Felton and four Mink were trapped on this river. Prints were found along the River Tweed in the Norham area and on the Till near the junction with the Tweed. Tracks were also found of a Mink along the River Aln near Alnwick in 1967 and on the River Wansbeck near Morpeth in 1968.

The history of Mink in Durham is not as well documented. Some of the earliest records include a dead individual killed in a rabbit snare on the river Deerness in April 1977 very close to the fur farm in Langley Wood, Langley Moor, which operated for about five-six years and closed in the late 1970s, a local farmer confirming that Mink had escaped from it. Bob Wilkin found Mink tracks and scats on the Bedburn in 1977 and a dead silver grey Mink near Chester-le-Street in 1983 (pers. comm. to Terry Coult, 2012).

Mink small

Mink hunting with hounds was established after otter-hunting became illegal in 1975 and the Northern Counties Mink Hounds hunted the region’s rivers until the Hunting Act of 2004 brought hunting with dogs to an end.

The density of Mink in an area can be related to the amounts of suitable habitats. In the UK, the Mink is normally associated with semi-aquatic habitats (Chanin, 1981; Birks, 1982; Dunstone and Birks, 1983), favouring eutrophic streams, rivers and lakes with abundant bankside cover (Birks, 1981). Mink dens are located near to the water’s edge depending on the availability of suitable den sites (Halliwell and Macdonald, 1995). Dens occur within or beneath waterside trees, in rabbit burrows, amongst rocks or above ground in scrub and brush piles. Denser populations can also develop on undisturbed rocky coastal habitats, providing there is plenty of cover (Harris and Yalden 2008). Mink do venture into urban areas where there is suitable habitat and have been recorded in the ponds outside County Hall in Durham City (Terry Coult, pers. comm., 2012).

Mink have been successful at establishing breeding populations across the UK as they have been able to fill a vacant ecological niche. They are opportunistic hunters, taking a range of prey including both terrestrial and aquatic species. Concern has been raised about the effects of predation by Mink on native species such as Atlantic White-clawed Crayfish Austropotamobius pallipes (Armitage, 2001), waterfowl, nesting sea birds and Water Vole Arvicola amphibius (Ferreras and Macdonald, 1999; Craik 1995, 1997; Woodroffe et al, 1990; Barreto et al, 1998; Strachan et al, 1998). The Mink has been found to have a negative effect on the populations of some riparian species (Ferreras and Macdonald, 1999) and is thought to be a major contributory factor in the decline of the Water Vole in the UK (Woodroffe et al, 1990; Barreto et al, 1998) including in Northumbria. The intensification of agriculture and reduction in riparian habitat has enhanced the impact of Mink predation on Water Voles.

The American Mink by Thomas Bewick

The Vincent Wildlife Trust undertook a comprehensive survey of Mink and Water Vole in Britain during the period 1996-1990 (Strachan and Jefferies, 1993), which showed that Northumbria supported medium to high densities of Mink (Strachan et al, 2003). The National Biodiversity Network (NBN) contains 208 Mink records between 1960 and 2011 for the region. Maps containing records for Mink can be downloaded for Berwickshire, Northumberland South, Durham and northeast Yorkshire (including Teesside). Records of Mink are clustered along the Tweed and Till catchments, rivers North Tyne, Tyne and South Tyne, river Wear and river Tees.

Our pre-2000 map shows the distribution of Mink in Northumbria using the 857 records provided during the period 1987-2000, by the Environmental Record Information Centre (ERIC). The percentage numbers of records for each river catchment area are shown in Table 1.

Table 1. The percentage numbers of Mink records from each river catchment area pre-2000

River Catchment Area Percentage number of records
North Tyne 29.7
Coquet 15.4
South Tyne 15
Wansbeck 10.7
Blyth 8
Tweed 6
Aln 6
Wear 4
Lyne 2.5
Tees 1.8
Leven 0.9

The majority of records are from the North Tyne catchment area, followed by the rivers Coquet, South Tyne and Wansbeck catchments. The Leven and Tees catchment areas contained the fewest records. Our post-2000 map shows the distribution of Mink in Northumbria using 131 records provided by ERIC during the period 2000-2011. The percentage numbers of records for each river catchment area are shown in Table 2.

Table 2. The percentage numbers of Mink records from each river catchment area post-2000

River Catchment Area Percentage number of records
Tees 28
Tweed 15.8
North Tyne 14.4
Wansbeck 12.2
Wear 6.5
Blyth 5.8
Leven 5.8
South Tyne 4.3
Coquet 2.9
Alne 2.9
Lyne 1.4

The river Tees catchment area held the greatest numbers of records of Mink followed by the Tweed, North Tyne and Wansbeck catchment areas. The Lyne catchment held the fewest records. The percentage numbers of records had increased post-2000 in the Tees, Tweed, Wansbeck, Wear, Blyth, Leven and Aln catchment areas, but had decreased in the North Tyne, South Tyne and Coquet catchment areas.

Differences may be due to changes in recording effort, the possibility that Mink may have been using a different area of their home range during surveys, a change in the distribution of Mink in the region or the numbers of Mink in the region declining. Proving that the numbers of Mink have actually changed in the region is difficult if not impossible. A survey commissioned by the Environment Agency in 2006 of Water Vole in the region also looked for Mink signs (E3 Ecology and Durkin, 2006). Survey results suggested that the numbers of Mink signs from the 300 survey sites had reduced in 2006 compared to the numbers of signs found from the same sites during a national survey in 1989/1990 (Strachan and Jefferies, 1993); however statistical analysis of this data was not possible. The reduction of Mink signs could be as a result of increased Mink control or from an increase in Otter Lutra lutra presence in most of the catchments in the region. Mink are less adaptable to hunting in the water than Otters and so expend more energy in catching aquatic prey (Dunstone, 1993). Perhaps Otters are better at exploiting the aquatic environment compared to Mink and are possibly out-competing Mink in some areas? Perhaps Mink are exploiting terrestrial habitats more in areas where Otter presence has increased? Evidence to support these hypotheses would require further investigations.

References

Written by Vicky Armitage (Last updated Nov 12)