The Otter Lutra lutra in Essex 1996-2002
serious threat to the re-establishment of populations. We know of 10 Otters (a minimum number)
killed by traffic in Essex since the Start of this survey.
In Britain, Philcox et al. (1999) considered 673 road deaths recorded between 1971 and 1996. They
found that more males than females were run over and that 91% of accidents occurred where a road
crossed a watercourse. More deaths occurred at times of spate when high water levels filled much of
the space under bridges and Otters left the river to continue the journey by crossing roads. It has long
been recognised that Otters will explore dry substrates under bridges and mark such sites with
spraints. Presumably a bridge appears as a significant feature within an animal's range and therefore
is used as a site for intra-specific communication. If no substrate such as rocks, earth or a concrete
ledge is available, the Otter is more likely to leave the river and cross the road especially at times of
high water levels (de Jongh 1991, Madsen 1996).
On the navigable and canalized sections of Essex rivers, e.g. the Chelmer/ Blackwater and Lea/Stort
systems, closed lock gates will also force animals to leave the water and cross roads. During our
survey we identified 22 bridges which require attention to make them more Otter friendly. Fourteen
of these were on busy A or Broads. For many years the provision of "'under-bridge" substrates has
been urged as a relatively simple aid to conservation (de Jongh 1991, Madscn 1996, Philcox et al,
1999). Philcox et al, (1999) suggested that new bridges could be designed with wide spans to incor-
porate a dry and natural substrate above the level of high flows. Culverts or dry tunnels and artificial
ledges have also been recommended (e.g. Madscn 1996). Clearly it is most cost effective to incor-
porate safe passages into the structure of new bridges and should now be automatic. In Essex, on the
River Colne, ledges have been provided on existing straight-sided bridges but these are stone-filled
wire gabions which Otters do not seem to like to walk on. The discomfort of walking on wire is
increased because high waters have washed away some of the stones filling the gabion leaving a
space between the stones and the surface wire. Given the urgency of the need for bridge modifica-
tion it is essential to explore cheap and rapid ways of dealing with the problem.
Fyke nets
Throughout Europe Otters drown in fyke nets that are set to catch Eels. Fykes are conical, multi-
funncllcd nets and eels which have entered them and become caught in the cod end will attract
Otters. The Otters then cannot find the way out and drown. The problem can be solved by fitting a
stop-grid to the entrance of the net that allows a reasonable catch of eels, but excludes Otters. The
introduction of stop grids is thought to have reversed the decline of Otters in Denmark and they arc
now mandatory in British waters. Unlicenced fykes still kill Otters (a female and her two cubs were
found drowned in Dorset in 2002) and in the past animals re-introduced on the Rivers Waveney and
Ant are thought to have died in these nets (Strachan & Jefferies 1996). In Essex there are extensive
Eel fisheries on the Blackwater catchment largely carried out seaward of the tidal limits but also
upstream on the Chelmer as far as Chelmsford.
Habitat protection
Essex rivers are extensively managed and manicured. Large bankside trees, the cavities caused by
erosion amongst the root systems of which may be used as holts by Otters, and stretches of riparian
woodland or scrub are uncommon. As human disturbance increases the need for shelter for wildlife
grows more acute. The commonest feature of Essex bankside vegetation is dense nettle-beds that
flourish due to the nutrients washed down by the river. The commonest riparian trees are scattered
alders and willows. The poor quality of bankside habitat in East Anglia, compared with Wales where
Otters are common, has been demonstrated by Mason & Macdonald (1990). A less exacting man-
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Essex Naturalist (New Series) 20 (2003)