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| The Site
Cultivated
landscape in the
border
area
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The
watersheds of three major rivers meet in northern Bavaria, close to the
boundary with the neighbouring German federal state of Saxony and the border
with the Czech Republic. These rivers are the Danube (Donau), the Rhine
(Rhein) and the Elbe. The highly endangered freshwater pearl mussel Margaritifera
margaritifera is found in tributaries of all three rivers in the hills
of the Fichtelgebirge, the Erzgebirge, the Frankenwald and the Oberpfälzer
Wald.
In
the shadow of the former Iron Curtain, the border area between Bavaria,
Saxony and the Czech Republic (known as the Dreiländereck), contains
some
of the most important populations of the freshwater pearl mussel that
have survived in the river system of the Südliche Regnitz. The common
river mussel Unio crassus is a second endangered naiad living
here. The mussels are an indicator of the extraordinarily high quality
of the streams. In particular, the pearl mussel thrives only in streams
and rivers that are very poor in lime and nutrients, which means that the
water is very clean.
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Freshwater
pearl mussels
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Common
river mussels (picture by Susanne Hochwald)
In
fact, the pearls in the streams are the mussels themselves. Only
one in every thousand of the thick-shelled animals produces a pearl, and
most of these are brown and lacklustre like peppercorns.
Common river mussel
and pearl mussel filtrate their food directly from the stream water. Existing
in a nutrient poor habitat, the pearl mussel lives a frugal life. Growing
quite slowly, the animal can reach an age of more than a hundred years.
The common river mussel survives in rivers with moderate nutrient contents
and is “only” capable of reaching the age of about 20 years old! Every
year, the female river mussel releases more than 10,000 larvae into
the stream water. The pearl mussel releases as many as several million
very tiny larvae. Only few of these are fortunate enough to be inhaled
by a host fish and to develop on the gills to a miniscule size.
The young mussels fall off the host fish and bury into the gravel on the
stream
bed until they have grown sufficiently to appear on the surface of
the sediment and start their monotonous existence of a filter feeder.
Young
mussels at the age of four
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Mussel
larvae on the gills of a trout
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Adult
pearl mussel, sticking out of the river sediment
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Threats
to the future survival of Mussels and Efforts to protect them
Silt
gets into the streams by many pathways
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For
centuries, large freshwater mussels have lived in populated areas and cultivated
landscapes. They survived the plundering of the mussel beds for pearl
fishing and for local industry using mother-of-pearl, as well as the alteration
of the streams for the establishment of water mills and ponds. But now
both kinds of mussels are threatened by extinction. The sewage of
an increasing population as well as the fertiliser surpluses from
intensive farming, owing to the need to produce multiple harvests as compared
with former times, bring nutrients and silt into the streams. Since
the improvement of sewage treatment, water quality has again become reasonably
good. However, for the common river mussel and even more so for the pearl
mussel adapted to very clean water, the quality is insufficient. The adults
no longer reach full age. But what is most serious is that the sensitive
young mussels no longer grow up. Consequently, the mussel populations
are elderly and declining.
Silt
damages the filtering mussels
Efforts have been
made in the Czech Republic, Saxony and Bavaria, over many years to re-establish
the former excellent quality of the mussel rivers. Far-reaching habitat
improvements are necessary, and consequently comprehensive measures
have already been carried out and will also need to be undertaken in the
future. Several projects have focused on joint efforts to establish protected
edges or strips of land alongside the mussel streams, to return main watercourses
and tributaries to their natural state, to achieve changes in land use
and remove the sewage from the river basins inhabited by mussels. Ultimately,
the conservation of mussels will only succeed if residents, institutions
and local authorities as well as representatives from the fishery, land
use, forestry and nature conservation sectors, work together. The European
Commission is funding two conservation projects in Saxony and Bavaria respectively
from the INTERREG Programme, in recognition of the European importance
of the mussel stocks, as well as the improvements already achieved.
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The Contribution of the Life-Project to Mussel
Conservation
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LIFE-Nature
is a EU-programme for species protection. Life-Nature funds projects that
aim to improve the habitat of endangered species in sites included in the
Natura
2000 network of protected areas. In 2002 five German Life-projects
were accepted for funding, including the project for mussel protection
in the border area – further recognition of the significance of this region.
The project is implemented and supported by regional environmental institutions
and the environmental ministries of the federal states of Bavaria and Saxony,
namely: Bayerischer Naturschutzfonds, Bezirk Oberfranken, Landkreis Hof,
Naturpark Erzgebirge/Vogtland, Bayerisches Staatsministerium für Landesentwicklung
und Umweltfragen, Sächsisches Staatsministerium für Umweltschutz
und Landwirtschaft.
The
contribution of the Life-project to the protection of the common river
mussel and the pearl mussel focusses on
1)
main pathways of silt and nutrients to the streams:
Silt traps at the
mouths of tributaries reduce the amount of silt entering the mussel streams.
The outflow from drainage pipes is opened and the drainage water is allowed
to trickle to the stream to avoid iron ochre clogging up the mussel habitat.
Ponds alongside the streams are purchased and transformed and land use
is extensified to avoid an increase in nutrients and silt.
2)
the lacking recruitment of mussels
Host fish of the common
river mussel and the pearl mussel are infected artificially with mussel
larvae. The developing young mussels that fall off the fish are set free
in specially prepared sections of the stream. In order to support the natural
recruitment of minnow, which is the main host fish of the common river
mussel, shallow sites and hiding places are established in the stream.
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Young
mussels as they fall off
the
host fish
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Juvenile
brown trout, infected with mussel larvae
and
marked on the tail for control purposes
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Unless stated otherwise, pictures are used by courtesy of Christine
Schmidt and Robert Vandé (Schmidt & Partner GbR). Please respect
copyright for all pictures. If you intend to use the pictures digitally
or by reproduction, please contact the authors. |
