The Otter Lutra lutra in Essex 1996-2002
derived almost entirely from released captive-bred animals.
Dobson (1999) provided a brief history of the Otter in Essex. He noted that, by 1970, Otters in Essex
were only reported from the Chelmer and Blackwater Navigation Canal, Fingringhoe and Bradwell
with the last record being from Ardleigh Reservoir in 1974.
There have been several reported releases of Otters into the area in recent years. Most of these
animals were bred at the Otter Trust at Bungay in Suffolk. The first group, comprising two sisters
and a male, was released on the River Ash, a tributary of the River Lea in neighbouring Hertfordshire,
in October 1991, while another two sisters and a male were released on the River Stort at Great
Hallingbury, in December 1991. Two months after this release a male Otter, thought to be from the
group, was killed on a road in Bishop's Stortford (Hertfordshire) (Roche et al. 1995). Two females
and two males were released onto the River Glem (a Stour tributary) in 1995 and another two
females and two males at Hamford Water (an area of shallow, tidal waters and salt marsh, south of
the Stour estuary) in 1996 (Environment Agency pers. comm.). In June 2000 two males and one
female Otter from a Hampshire Rescue Centre were released into the very small Dodnash Brook,
Suffolk, which flows into the Stour estuary (Sarah Norman pers. comm.).
The Otter is a priority Biodiversity Action Plan species within Essex. This study was carried out to
determine and evaluate any trends in the status and distribution of Otters in Essex from 1996 to
2002, to assess any threats to the species within the county, and to suggest conservation actions that
may ensure the future of Otters within the county.
Methods
During October and November 1996 an initial survey of all rivers in Essex was undertaken. From
1997 to 2002 the same rivers were monitored each spring between February and May. Rivers in-
cluded the Stour, together with its Suffolk tributaries, the Colne, Blackwater (called the Pant in its
upper reaches), Chelmer, Crouch, Mardyke and Roding, those stretches of the Stort and Lea which
form the western boundary of the county and the top stretch of the Cam. Some potentially suitable
coastal stretches were also surveyed. Survey sites started at bridges or at points of easy access and
up to 600m of bank were searched for signs of Otters, viz. spraints and footprints. As soon as signs
were found the search was terminated. The methodology follows the standard method first devel-
oped for the British national surveys. Where a series of consecutive sites were found negative which
had been positive the year before, they were resurveyed, sometimes twice, to confirm their change in
status. The distribution of survey sites is shown in Figure 1 overleaf.
A thriving population of Otters will utilize long stretches of river and mark sprainting sites heavily.
The percentage of positive sites for Otters and the sprainting intensity (mean number of spraints per
sprainting site) have been combined into an index of population performance for a catchment (Ma-
son & Macdonald (1993b). The index is:
I=p/10+10[log(x+1)]
where p is the percentage of positive sites over all surveys in the year and x is the mean number of
spraints per sprainting site for the year.
Essex Naturalist (New Series) 20 (2003)
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