The Otter Lutra lutra in Essex 1996-2002
River Stour catchment
In 1996, 30 sites on the main river Stour were surveyed and 20 were found to be positive for Otters.
According to the Environment Agency (pers, comm.) Otters bred near Flatford. No signs of the
species were found in the headwaters above Gt. Wratting and nothing was found in the tidal reaches.
Otters were located on four Stour tributaries, namely the Glem, the Chad Brook, the Box and the
Brett. Overall, of 59 sites surveyed throughout the Stour catchment, 63% proved positive.
In 1997,23 of the main river sites had signs of Otters. On the tributaries, the distribution on the Chad
Brook, Box and Brett remained unchanged but on the Glem an animal had ventured up into the
headwaters. Overall, throughout the catchment, 66% of sites were positive.
Results in 1998 saw a marked reduction in Otter distribution on the Stour. On the main river 18 sites
proved positive but there was no sign of last year's explorer in the headwaters of the Glem and
nothing at all was found on the Box. Overall, 46% of sites produced evidence of Otters, a significant
reduction from the 66% of the previous year.
A further worsening of the situation occurred in 1999 with only 13 positive sites on the main Stour.
On the tributaries only one site on the Glem produced signs and the Box remained empty. A slight
increase in range upstream on the Brett was recorded but this may have been related to increased
water levels that may have encouraged a movement of fish. Throughout the catchment only 38% of
sites proved positive.
Little improvement occurred in 2000 with an overall result of 43%. Spraints were again found on the
Glem but fewer and with a reduced range, a pattern observed since 1997 and also found on the Chad
Brook. However, signs did appear again on the River Box and numbers of spraints on the Brett
increased with tracks of cubs being recorded. The confluences of the Box and Brett with the Stour
are close and so signs found on the two rivers may have derived from the same group. Also in this
year spraints were found for the first time at Alton Water, a water supply reservoir, with an outflow
to the Stour estuary.
In 2001 most of the Stour catchment had been surveyed before the onset of the foot and mouth
epidemic. On the main river 15 sites were positive, an improvement on the previous two years, with
more sites on the upper reaches being occupied. On the tributaries, signs were again found on the
Chad Brook, Glem and on the Box near to its confluence with the Stour. The Brett remained the
tributary with the most signs and the most indication of an established population. Throughout the
catchment 55 sites could be checked and 56% were positive.
The final survey was conducted in 2002 and produced an overall positive result of 57%. On the main
Stour distribution extended from the headwaters to Manningtree at the tidal limit. Cub tracks were
recorded on the middle reaches near Bures. There was little change in numbers of marked sites on
the Glem, Chad or Box but the Brett remained reliable, with 10 of the 12 sites positive. The Stour
catchment in 2002 therefore seemed to have returned to a semblance of the level of occupation
recorded in 1966/67 with the interim period of 1998 - 2000 demonstrating a progressive decline.
The index value for the Stour catchment (Fig. 10) shows a decline over the period 1996-1998,
followed by a very shallow increase to 2002.
Essex Naturalist (New Series) 20 (2003)
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