The American Mink Mustela vison in Essex
CHRIS MASON & SHEILA MACDONALD
Depart/nerii of Biological Sciences, University of Essex, Colchester C04 3SQ
Abstract
The distribution of M ink in Essex and the adjacent Suffolk tributaries of the River Stour was recorded
during routine surveys for Otters Lutra lutra during 1996-2002. Of 234 sites surveyed each year,
signs of Mink were observed at 69 during the study period. They were distributed especially in the
middle reaches of the Rivers Stour, Colne, Blackwater, Chelmer and Roding and the Essex reach of
the Cam. The significance of the colonization to conservation interests is discussed.
Introduction
The first records of wild-bred American Mink Mustela vison in the UK were from Devon in 195 6.
Mink had been reported from 63 counties in the UK by 1967 and from 70 counties by 1971. Much
of this apparent spread was due to small-scale escapes of animals from fur farms (Harris et al.,
1995). In Essex the first documented case of mink was one at Abberton Reservoir in 1962 (Dobson,
1999). Dobson observed that since 1980 Mink have been reported from a number of widely scattered
localities in Essex, though they have never been common. We report here on the presence of mink
recorded during annual surveys for Otters Lutra lutra in Essex over the period 1996-2002.
Methods
The standard method for surveying Otters was used with up to 600m of riverbank being searched
for signs (scats, footprints) of the animals, starting at a bridge or other suitable access point. Some
coastal areas were also surveyed. As the survey was primarily for Otters, when signs of this species
were located, the search was terminated. A total of 234 sites were surveyed in each year.
Results
The distribution of Mink in Essex recorded over the period 1996-2002 is shown in Fig. 1. The
species was located at 69 sites. Signs were found in the upper reaches of the River Stour, its Suffolk
tributary the River Brett, and on the Colne, Blackwater and Chelmer catchments. Mink were also
found over much of the length of the upper River Cam in Essex, where one was observed killing a
rat Rattus norvegicus in 2001, on much of the River Roding, and on the Stort. On the River Lea,
signs of Mink were found only at Walthamstow Marshes within London and they were also located
at two places on the Thames Estuary but at no other coastal site.
Fig. 2 shows the number of localities positive for Mink over the years 1996-2002, excluding 2001
when coverage was incomplete due to the foot and mouth epidemic. There was a clear increase in
the number of positive localities in the final year of the study.
Discussion
Because our survey was primarily concerned with Otters, searches were terminated as soon as
signs of this species were found. The distribution map of Fig. 1 must therefore be considered as the
minimum distribution of Mink in Essex. While the number of positive sites for Mink varied from 8
to 15 in each year over the period 1996-2000, there was a marked increase in positive locations in
Essex Naturalist (New Series) 19 (2002)
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