Geoscience Reference
In-Depth Information
2400
1
1800
0
Precipitation
Recruitment
1200
-1
1955
1960
1965
1970
1975
1980
1985
1990
1995
Year
Figure 10.4
Historical precipitation and freshwater pearl mussel recruitment patterns in the River Kerry, Northwest
Scotland (1955-1995). From: Hastie
et al.
(2003a)
Ambio
32
: 40-6, with kind permission of Springer Science
+
Business
Media B.V.
Habitat reduction
Successive studies into pearl mussel populations
have demonstrated that many Scottish rivers and
streams currently lack juvenile mussels (Cosgrove
et al.,
2000a; Hastie
et al.,
2000b), suggesting that
recruitment in these populations is limited. For
example, 53 Scottish rivers (25%) currently hold
populations of adult mussels and host fish but
with no evidence of recent successful juvenile
recruitment (Table 10.1). It is not clear what
has caused this, but based on the often large
number of adult mussels present, there must have
previously been substantial amounts of suitable
juvenile habitat in many rivers. It is very difficult to
quantify this change or say why it has come about
because several detrimental factors may already
have contributed to the decline of these mussel
populations and there are no pre-decline baseline
data to compare with (nor, in most cases, current
data on host fish populations).
This phenomenon is particularly apparent in
small west-coast streams, many of which now
appear to be highly unstable and therefore
unsuitable. Since 2006, SNH has conducted a
series of detailed habitat surveys to investigate
reintroducing pearl mussels into former river
catchments. The aim of these surveys has been
(although two do not have significant lakes
ameliorating river flows) and in recent years each
of these catchments has had very large flood events
and SNH monitoring indicates they still support
pearl mussels and suitable habitat. So, while
many extant Scottish pearl mussel populations are
considered vulnerable or susceptible to UKCP09
high precipitation projections for 2070-2090, the
high proportion with upper catchment lakes
may mitigate against some of the more extreme
effects. Thus, less extreme UKCP09 projections
for increased precipitation within catchments
where lakes are present may actually help
to increase successful reproduction in some
populations through cleaning and aerating stable
pearl mussel habitats.
Indirect climate change effects
The impact of climate change on pearl mussels
is not straightforward, with potential effects
poorly understood or operating in apparently
contradictory ways. Four indirect effects are
predicted to occur and the magnitude of these is
likely to vary greatly between catchments.
