The Otter Lutra lutra in Essex 1996-2002
Discussion
Otters suffered a drastic decline in both range and numbers over much of Britain from the late 1950s
and they became extinct in Essex in the early 1970s (Dobson 1999). The species began re-coloniz-
ing the county in the 1990s when two of 22 survey sites on the River Stour and one of 20 sites on the
Colne were positive (Strachan & Jefferies 1996). Animals were also present on the upper Cam.
During our surveys between 1996 and 2002 the number of positive records has increased substan-
tially from that time but distribution has fluctuated considerably with some positive evidence ap-
pearing and then disappearing.
The origins of the Otters that appeared in Essex in the 1990s are largely unknown. Strachan &
Jefferies (1996) suggested that their findings on the Stour may have indicated a movement from
Suffolk where a number of releases of captive-bred Otters had been carried out since 1983 (Jefferies
et al. 1986). Suffolk rivers, such as the Black Bourne, that now have firmly established breeding
populations (pers, obs.), have headwaters close to those of the Stour and Colne.
Natural colonization from the west could be a possibility but while the species is steadily expanding
and consolidating in England from west to east, it is unlikely that, for example, populations in the
upper Thames arc substantial enough to provide sufficient animals to found an Essex population.
There are recorded releases of captive-bred Otters into the River Lea catchment, the Stour and
Hamford Water, all involving very small potential breeding units. There are other suspected re-
leases and some of our survey results suggest that this has occurred. For example on the Colne,
although Otters had been rumoured to be present since 1992, Strachan & Jefferies (1996) found only
one positive site in 1994 and we found no signs during a preliminary survey in 1995. However, in
1996, 43% of sites proved positive with a distribution covering almost the entire length of the main
river. By 1999, nothing again could be found.
There have been rumours of a release at Hanningfield Reservoir and a release was also rumoured at
Abberton Reservoir. Abberton Reservoir discharges into the Roman River, a tributary of the Colne.
Sightings were recorded at Abberton in May 2000 and on the Colne near to the Roman River
confluence in the previous month. Two Otters were killed by traffic in this area in September and
December 2000.
On the River Roding signs suddenly appeared in 1999 with heavy marking in Wanstead Park, well
within the London boundary. The level of marking persisted into 2000 but signs found on the river
in 2002 suggested that possibly only one animal remained.
Such results suggest that clandestine releases have been taking place, in addition to those that have
been officially reported, though there is no concrete evidence. However, it should be stressed that
surreptitious releases are a disservice to conservation efforts. The fates of the animals cannot be
monitored, the major threats they encounter and the limiting factors in the re-establishment of the
species cannot be assessed. The absence of careful monitoring of reintroductions and their poor
documentation in the published literature ensures that the overall distribution picture means less
than it should (Hodder & Bullock 1997, Fischer & Lindenmayer 2000). Are the findings the result of
natural re-colonization or due to secret introductions? Under such circumstances little can be learned,
while the future of the Otter in Essex is made difficult to predict.
Despite difficulties in interpreting the findings, the situation in Essex in 2002 can be summarized.
On the Stour the distribution of Otters appeared to have returned to the situation found in 1996
Essex Naturalist (New Series) 20 (2003)
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