Fen Management Handbook - Scottish Natural Heritage

and Killeen and Moorkens (2003) covers Desmoulin’s whorl snail (available from
http://www.english-nature.org.uk/LIFEinUKRivers/species/species.html). Advice and
training is also available from specialist societies such as Butterfly Conservation.
Highly competent amateurs with a particular interest in groups such as moths,
dragonflies and damselflies may well provide a self-funding, self-managing, longterm
monitoring service.
Unlike botanical monitoring, which may need repeating every three to five years,
the population of key invertebrate species may need annual monitoring because of
the rate of fluctuation, for example because of adverse weather conditions during a
brief mating season. Long term monitoring is needed to show a clear trend, and if
the trend is downward it may be associated with a change in the plant community.
As with plants, the potential loss of a visually striking and uncommon species is
more likely to draw in funds for habitat management than ‘an evident decline in
the diversity and extent of the S27 fen community’. However, the presence of a
notable species depends on the right habitat to support that species, and it is
the maintenance of that habitat or particular vegetation community that is crucial.
This may be related to water quality/quantity, vegetation structure or species
composition.
The open water component of a fenland habitat mosaic is not suited to botanical
monitoring unless it is mesotrophic or moderately oligotrophic lowland lake. If
the water is at all enriched the dominant plants will be algae, either planktonic
or filamentous. Work on algal populations is highly specialised, but a simple
measurement that can be made is routine turbidity estimation with a Secchi disk.
In this habitat, invertebrate community monitoring can provide direct evidence of
the habitat quality, but usually requires a boat and laboratory work. A less rigorous
technique is to record date, species and intensity of insect hatches as part of daily
observation log on sites with full-time staff. Trichoptera (caddis fly) species are
sensitive to water quality, whereas some of the large chironomids (biting midges)
are highly adapted to low oxygen conditions. Consequently a decline in the sedge
hatches and a reduction in the number of chironomid hatches, leading to a few
massive hatches of large midge species, is a strong indication of declining diversity
due to water quality factors.
10.5 Biological monitoring techniques – vertebrates
Monitoring vertebrate species as indicators of habitat quality on fens is complicated
by the fact that most vertebrate species found in fens are either readily observable
and highly mobile, or hard to observe generalist feeders or species such as grass
snake or water shrew with a high dependence on wetland habitat which are very
good at hiding in it, and consequently almost impossible to record.
Birds, bats and otters all forage in wetland areas and some species are wetland
specialists, but they will cover a large area and may be foraging elsewhere when
a count is made. Their numbers and activity may be a measure of habitat quality at
the landscape scale, or relate to distant sites in the case of migratory birds. Fen
vertebrate monitoring therefore involves monitoring key species, where they occur,
which are dependent on the habitat being in favourable condition.
Some vertebrate species, such as water voles, feed on a wide range of plants
and remain in a limited area but the population may be limited by the availability of
suitable burrowing sites with adjacent cover above the flood line.
Competent voluntary monitoring is carried out at many fenland sites: the wetland
bird survey and the Daubenton bat waterway survey are good examples of well
established programmes involving many professional ecologists. The British Trust
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