The Otter Lutra lutra in Essex 1996-2002
Coggeshall). Additional surveys were made in the Blackwater estuary in 2002 but no signs were
found. Despite animals having existed on this system for the past six years, they have not apparently
expanded their range.
The index (Fig. 10) has fluctuated at a rather low level over the period, suggesting that the popula-
tion remains well below its potential.
River Chelmer catchment
The River Chelmer is joined by four main tributaries - the Wid, Can, Sandon Brook and Ter. In 1996
only one of 38 monitoring sites on this system proved positive for Otters, a result that increased to
three in 1997. In 1998 seven sites (18%) had evidence of the animals, improving to 13 (34%) in
1999 with positive sites recorded on the Can and Stebbing Brook. Results for 2000 demonstrated a
gradual consolidation since 1997 but no expansion in range. Only 16 sites could be surveyed in
2001 but animals were still present in the lower half of the main river, on the Wid and Can and also
on the Sandon Brook. In 2002, 14 of the 38 standard sites (37%) had Otter signs but only the
downstream stretches of the main river were colonised and use of tributaries appeared to be limited
to the junctions with the main Chelmer. As with the Blackwater, the species is present but seems to
be struggling and so far failing to expand its range.
The index value (Fig. 10) appears to have stabilized somewhat below 10, again much below the
potential for the river.
South Essex catchments
The Rivers Crouch, Roach, Mardyke, Ingrebourne, Beam and Thames were surveyed, including
adjacent coastal areas (a total of 18 sites). Throughout the survey period no signs of Otters have
been found.
River Cam catchment
Throughout the survey period the Cam has held Otters from close to its source to Great Chesterford,
i.e. much of its length in Essex. Numbers of spraints have never been high, suggesting that these
upper reaches, while occupied, do not hold a thriving population. Because such a small part of the
Cam catchment is in Essex, no index has been calculated.
River Roding catchment
No evidence of Otters was found on the Roding until 1999 when suddenly nine of 19 survey sites
were positive with a range from upstream of Ongar to Wanstead Park in Ilford, London. Surveys
further downstream to the confluence with the River Thames have proved negative. In 2000,44% of
sites had signs, Ilford Park showing the highest number, with 14 spraints beneath a bridge. However
the number of positive sites fell to four in 2001 and to only three in 2002, with a level of sprainting
that suggested possibly only a single animal remained on the system (Fig. 10). The distribution in
2002 was restricted to the stretch between Ongar and the Roding Valley Meadows north of Chigwell.
River Lea catchment
Only part of the River Lea flows through Essex, downstream of its confluence with the River Stort.
The number of positive sites found in each year has remained rather low. Three of 17 sites (18%) in
1996, three of 18 (17%) in 1997, seven of 18 (39%) in 1998, seven of 17 (41%) in 1999, five of 18
Essex Naturalist (New Series) 20 (2003)
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