Geoscience Reference
In-Depth Information
Table 10.1
The status of freshwater pearl mussels in Scottish rivers, 2010.
Number of
watercourses
Status
Total number of historic pearl mussel rivers
208
Total number of historic rivers where pearl mussel population is 'apparently extinct' in the wild
62
Total number of historic rivers where pearl mussel population is 'not successfully recruiting' in the wild
53
Total number of pearl mussel rivers where there is evidence of 'recent successful recruitment' in the wild
71
Total number of pearl mussel rivers, where population status is unknown i.e. no survey data available
22
Total number of pearl mussel rivers where proportion of juveniles
>
10% of population
25
Total number of pearl mussel rivers where population exceeds 10 000 individuals
26
dataset, has been used to provide an up to date
assessment of the species status in Scotland (Table
10.1). Of 208 watercourses known to be occupied
100 years ago, pearl mussels are extinct or about
to become extinct in approximately two-thirds.
Nevertheless, as a consequence of the severe
decline across the species' range, the remaining
71 Scottish rivers with recent juvenile recruitment
(Figure 10.2) represent a large proportion of the
remaining global population. When consideration
of climate change effects is quantified this is done
in relation to the 71 extant Scottish pearl mussel
populations where juvenile recruitment currently
occurs.
Direct climate change effects
It has long been known that climatic variables,
particularly extremes of temperature and
precipitation, affect animals. In the case of
pearl mussels, climate changes may influence a
number of factors important for survival, including
growth, longevity, reproductive success, habitat
and host fish availability. These potential effects
are considered alongside the latest climate change
prediction models for Scotland (known as UKCP09
projections). For simplicity the data have been
extracted for one 25 km square (the resolution
projections work at) in the middle of the extant
Scottish range of the pearl mussel. This square
is centred on the village of Gairloch, midway
along the Scottish west coast. The 'high emissions'
scenario has been selected and projected summer
temperatures and precipitation based on July
data and projected winter precipitation based on
January data have been used. The species occurs
between 40
o
Nand70
o
N, (with Scotland in the
mid range 55-60
o
N)andsopredictedwinter
temperature projections are unlikely to affect
freshwater pearl mussels.
The UKCP09 projections do not provide flow
data for river levels, so precipitation has been used
as a proxy for flow. There is typically a strong
relationship between air and water temperature
across a range of catchment sizes (Smith and
Levis, 1975) and so likely mean air temperature
changes from the UKCP09 projections are used as
Figure 10.2
A typical range of pearl mussel sizes in a
viable (reproducing) population.
