1. One hundred and sixty rivers in Scotland with historical records of fres
hwater pearl mussel Margaritifera margaritifera were surveyed between 1996
and 1999 for the presence of the species.
2. M. margaritifera populations were classed as either 'extinct' (no mussel
s remaining),'not currently viable' (ranging from only dead shells present
to no juveniles present, regardless of the number of adults found), or 'fun
ctional' (at least one juvenile was found, regardless of the overall number
s of adults present).
3. M. margaritifera populations could be classed as functional: in only 52
rivers (34% of total surveyed) and in only 17 of these were juveniles below
20 mm (5 yrs old) present. Furthermore, in only 10 of these functional riv
ers were mussels also still considered either to be common or abundant and
these included both large easterly-flowing rivers and small western rivers
4. In approximately two-thirds (101) of the 155 rivers occupied 100 years a
go, M. margaritifera is now extinct or is about to become extinct. Furtherm
ore, analysis indicates that the rate of mussel population extinction has a
ccelerated since 1970, with a recent average of two mussel river extinction
s per year.
5. The predominant threat to the mussel populations has undoubtedly been pe
arl fishing. This has been occurring at every river, even in the most remot
e northwest areas, where most of the 'functional' populations remain. Recen
t legislation has provided full protection to M. margaritifera, so that all
pearl harvesting is now illegal.
6. Locally, river engineering and host salmonid stock decline poses a serio
us threat and eutrophication has already eliminated populations in southern
and eastern Scotland.
7. In every part of its global range, M. margaritifera has declined substan
tially and is now either threatened with extinction or is highly vulnerable
. Based on recent estimates from across the species range, it appears that
Scotland now probably holds at least half of the world's remaining function
al M. margaritifera populations. Copyright (C) 2000 John Wiley & Soils, Ltd