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but especially small streams where temperature
fluctuations are likely to be greatest.
Increased precipitation, with resultant
hydrological changes, may also have serious
consequences for host fish. Spawning beds are
sometimes destroyed and washed out of rivers
by large floods, along with juvenile fish. Butler
(1999) reported negative correlations between
winter runoff and declines in densities of salmon
fry in a river the following year in the north west
of Scotland. In 1997, a 1 in 100 year return flood
'washed out' large numbers of juvenile fish from
the River Oder in Central Europe (Bishoff and
Wolter, 2001). This suggests that significant floods
may have the combined detrimental effect of
killing large numbers of pearl mussels and juvenile
fish, and destroying suitable mussel substrate and
fish spawning habitats, scenarios predicted to be
likely to increase in frequency with increasing
precipitation events.
Societal responses
The way society responds to climate change will
directly affect the likelihood of endangered species
such as
M. margaritifera
surviving into the future.
Responses can be divided into two categories:
adaptation (dealing with the consequences of
climate change) and mitigation (preventing or
reducing the severity of climate change).
Figure 10.5
Adaptive responses to threats posed by
climate change have typically manifested themselves
through large-scale river engineering activities (e.g.
building flood defence walls to contain watercourses and
digging out channels to make them deeper) and
unsurprisingly this is hugely detrimental to the
ecosystems of the watercourses affected. From: Hastie
et al
., 2003a. Ambio 32: 40-46, with kind permission of
Springer Science+Business Media B.V.
Adaptation
As a result of recent increases in precipitation and
large-scale flooding in Scotland, there is strong
political pressure to reduce the effects of flooding
on people's homes and livelihoods. Typically, this
manifests itself as a desire to build flood defences
through large-scale river engineering activities
(e.g. building walls to contain watercourses and
digging out channels to make them deeper) and
unsurprisingly this is hugely detrimental to the
ecosystems of the watercourses affected (Figure
10.5). Pressure to reduce the effects of flooding can
increase changes in catchment drainage patterns.
Drainage increases the amplitude of flood effects,
creating faster and more intensive flow patterns
than would otherwise occur.
River engineering has historically been
responsible for the decline and extinction of
many freshwater pearl mussel populations, with
up to 10 000 mussels killed and 95% of suitable
habitat destroyed (Cosgrove and Hastie, 2001) and
indeed is one of the reasons why the species is
now threatened. Cosgrove
et al
. (2000a) found that
river engineering was responsible for the decline of
at least 26 pearl mussel populations in Scotland.
