Origin of Name
The Abernethy Pearl, a 44-grain extraordinary
freshwater pearl discovered in the River Tay in Scotland from a
freshwater Unionoidae mussel species known as Margaritifera
margaritifera, once common in the rivers of
Scotland, gets its name "Abernethy," as well as its nickname "Little
Willie" from William Abernathy, the professional pearl diver who
discovered the pearl in 1967. Scotland had been famous for its
freshwater pearls since ancient times, and some historians believe that
the exceptional quality of these pearls was one of the main reasons that
led the Roman Emperor Julius Caesar to invade Britain.
Characteristics of
the Pearl
The Abernathy Pearl discovered from the freshwater
Unionoidae mussel species Margaritifera margaritifera in Scotland is an
exceptional pearl in terms of size, shape, color, luster, and
surface quality and the
combination of all these desirable characteristics have made the pearl
one of the most perfect freshwater pearls ever to be discovered not only
in Scotland, but perhaps in the whole world, and is therefore listed among the most famous pearls in the world.
For Images of the Abernethy Pearl, Please Click Here (External Link)
In any pearl grading system six basic pearl traits
are used in determining the quality and value of pearls. These are,
size, shape, color, luster, surface quality and nacre quality.
Size of the pearl
Size of the pearl is one of the crucial factors that
determine the quality and value of pearls. Normally larger the size of
the pearl greater is its value. In the case of natural pearls size is
dependant on the size of the oyster that produced the pearl, the length
of time the pearl had grown inside the oyster, climatic and other
environmental conditions. However, size is not always associated with
quality. Smaller pearls do exist which are of higher quality than larger
pearls of poor quality. Size of a pearl is indicated both in terms of
its dimensions and weight. Dimensions are given in millimeters and the
weight in carats or grains.
The dimension (diameter) of the Abernethy
Pearl is not known, but the size of the pearl is said to be comparable
to the size of an average marble, which usually has a diameter of about 12.5 mm.
The weight of the pearl is 2.2 grams, equivalent to 11 carats or 44
grains. Thus the Abernathy pearl can be considered as a medium sized
pearl in comparison to other natural pearls.
Shape of the pearl
Pearls are found in seven basic shapes. These are 1)
round 2) near-round 3) oval 4) button 5) drop 6)
semi-baroque 7) baroque. The GIA classifies pearl shapes into
three main categories. They are :- 1) Spherical 2) Symmetrical and
3) Baroque. Round and near-round pearls come under the spherical
category, and have a uniform diameter or nearly uniform diameter all
round. Oval, button and drop shapes are considered as symmetrical
shapes, and can be divided into two equal halves through a median line.
Semi-baroque and baroque are irregular shapes without a line of symmetry
and fall under the baroque category.
1) Spherical - round and near-round
2) Symmetrical - oval, button, drop
3) Baroque - semi-baroque and baroque
Among natural freshwater pearls the commonest shape
is baroque. Symmetrical shapes are rare; but the rarest of all shapes in
freshwater natural pearls is the round shape. The perfectly round shape
is the most desired shape for all types of pearls, whether freshwater or
saltwater.
The Abernathy pearl has an astoundingly perfect
spherical shape, the most desired shape for pearls, but extremely rare in natural freshwater pearls.
Color of the pearl
A pearl's color is the net effect of three traits,
known as hue, overtone and orient. Hue is the overall pearl color that
one sees on first impression. Overtone, which may or may not be present
is the secondary color associated with the main color, such as pink
associated with white known as pinkish-white. The orient or iridescence
of a pearl, also not always present, is a colorful rainbow-like sheen
caused by the scattering of light by the aragonite platelets in the
nacre. Freshwater pearls occur in a wide variety of colors than natural
pearls. Some of the colors found in freshwater pearls are white, cream,
yellow, pink, rose, lavender, purple, blue, green, brown and red. Common colors found in
Scottish freshwater pearls are white, gray, cream, peach and lilac.
The
Abernethy pearl is a pinkish-white pearl, with a white hue and a
slightly pink
overtone.
Luster of the pearl
Luster is the most important of all factors as far as
the beauty of a pearl is concerned. Luster is responsible for the
so-called inner glow of the pearl, that sets them apart from other
gemstones. Luster is a measure of the quality and quantity of light that
reflects from the surface and just under the surface of a pearl. It is
the reflective quality and brilliance of the surface of the pearl's
nacre. The more lustrous a pearl, the more it shines and reflects light
and images. When the luster is low the pearl appears white and chalky
and has a matte-like appearance. Generally saltwater pearls tend to have
a greater luster than freshwater pearls. Luster is dependant on
the thickness and translucency of the nacre. In general thicker the
nacre the more lustrous is a pearl. A high quality luster results only
when the nacre is translucent and the aragonite plates overlap in such a
way that the pearl appears lit from within.
The Abernethy Pearl, in spite of being a freshwater
pearl has a striking luster, almost equivalent to the luster of
saltwater pearls.
Surface quality
Pearls being creations of nature always have flaws
and blemishes on their surface, to the extent that their presence is a
proof of their genuineness. A hundred percent blemish-free pearl does
not exist. A pearl that appears blemish-free to the naked eye, may still
show some blemishes under a magnifying glass or microscope. GIA
classifies surface quality into four categories :- 1) Apparently
blemish-free or spotless, or contain minor blemishes not visible to the
naked eye. 2) Lightly blemished 3) Moderately blemished
4) Heavily blemished.
The Abernathy pearl is apparently blemish-free and
without doubt falls under the first category of this classification.
Nacre quality
As mentioned earlier nacre quality is directly
related to the luster of the pearl. Nacre quality refers to both the
thickness and translucency of the nacre. The depth or thickness of nacre
layers can be determined only by inner inspection using optical fibers
and soft X-ray apparatus. However careful visual examination might give
a rough indication of the quality of the nacre. A dull chalky appearance
is usually associated with a thin nacre. In the case of cultured pearls
the nacre may be quite thin that even the bead nucleus shows through. A
pearl with a good luster is usually associated with a thick translucent
nacre.
The Abernethy pearl with its exceptional luster is
undoubtedly associated with a naturally created thick translucent nacre.
History of the
Abernethy Pearl
History of the
exploitation of freshwater mussels in England, Scotland, Wales and
Ireland
The invasion of
Britain by Julius Caesar in 55 BC was prompted by Scottish pearls
The History of the exploitation of the freshwater
mussel Margaritifera margaritifera in Britain dates back to over 2,000
years to the pre-Roman period. During the Roman period in 55 BC, one of
the four reasons given by Julius Caesar for invading Britain was to take
control of the trade in Scottish freshwater pearls, which together with
gold, underpinned the Roman monetary system. Historical evidence shows
that Roman ships reached as far as the Persian Gulf and the Gulf of
Mannar to purchase pearls for the royalty in Rome.
Commercial
exploitation of freshwater mussels in Britain and Ireland
In the 12th century, Scottish pearls were traded in
the pearl markets of Europe, and by the 16th century commercial
exploitation of the freshwater mussel had developed into a large scale
industry in Britain and Ireland. During this period the Government
employed river bailiffs to supervise the exploitation of freshwater
mussels and to ensure that all valuable pearls reached the King's
treasury. Scottish pearls of exceptional quality entered the crown
jewels of both England and Scotland during this period. Some of the
monarchs of this period were notorious for adorning themselves with
pearls both as jewelry such as multi-strand necklaces, earrings,
bracelets etc. and pearl-studded dresses. The famous Armada
portrait of Queen Elizabeth I (1558-1603), gives an
indication of the extent to which pearls were valued as adornments by
the monarchy, during this period. Another example of the use of pearls
by the monarchy is given by the portrait of Mary, Queen of Scots
(1542-1587).
Mary, Queen of Scots
Queen Elizabeth I of England-
Armada Portrait
Small scale
exploitation continued into the 20th century, and led to the discovery
of the Abernethy pearl in 1967
The commercial exploitation of freshwater mussels in
Britain and Ireland continued into the 19th century, but over
exploitation without regard to conservation and restoring oyster
populations, made the fishery unsustainable, and production declined
rapidly and was later abandoned altogether. An interesting parallel is
found in the Gulf of Mannar, in Sri Lanka, a source of pearls since very
ancient times, which became unsustainable after large scale commercial
exploitation by the British Colonialists in Sri Lanka in the 19th
century. This is in contrast to what happened in the Persian Gulf, where
non-interference by the government in pearling activities was able to
sustain small scale pear fisheries for centuries without any
interruption, until the early 20th century, when cultured pearls
produced by Mikimoto flooded the international pearl markets.
Small scale pearl fishery by individual pearl divers
and the gypsies
in Britain and Ireland continued well into the 20th century, until a
total ban was imposed on pearl fishing in 1998. It was during this
period of small scale pearl fishery, in 1967 that a professional pearl
diver by the name of William Abernethy, operating independently,
discovered the extremely rare natural freshwater pearl of outstanding
qualities, in the River Tay that came to be known as the Abernethy Pearl aka the Little
Willie Pearl.
The habitat of the
freshwater pearl mussel Margaritifera margaritifera
The freshwater pearl mussels Margaritifera
margaritifera inhabit fast-flowing, unpolluted rivers and streams and
are normally found buried or partially buried in coarse sand and fine
gravel with their siphons exposed. The mussels can rebury themselves if
dislodged, and can also move slowly across sandy sediments. The abundant
supplies of oxygen found in fast flowing rivers and streams, and
suspended food particles are conducive to the growth of the mussels. However
development is slow and the young mussels reach maturity only after
10-15 years, when the length of the shell generally exceeds 6.5 cm (65
mm). The growth slows down in older mussels. As the mussels grow annual
growth rings are laid down on the shell, like growth rings on tree
trunks. By counting the growth rings under a microscope one can estimate
the approximate age of the mussels. Using this method scientists have
found that the pearl mussel Margaritifera margaritifera outlives human
beings, some individual mussels living up to the age of 140 years,
and reaching a maximum shell length of 12-15 cm (120-150 mm). The
mussels inhale water through their exposed siphons, and filter out
suspended organic particles on which they feed. In waters where large
populations of mussels live, the filter feeding process helps to purify
the water, that can be beneficial to other species living in the same
environment such as the juvenile Atlantic salmon (Salmo salar) and brown
or sea trout (Salmo trutta). It has been estimated that a single mussel
can filter up to 50 liters of water in a day.
1. Posterior adductor muscle
2. Anterior adductor muscle
3. Frontal gill
4. Back gill
5. Exhalant aperture
6. Inhalant aperture
7. Foot
8. Pseudotooth
9. The hingeline and ligament
10. Mantle
11. The shell's thickest part, the umbo
Anatomy of Margaritifera Margaritifera
A collection of live Margaritifera margaritifera-
Photo taken from a river bed in Sweden
Photo above ,Creative Commons
The River Tay, from
which the Abernethy Pearl was discovered
The River Tay, which is the longest river in Scotland
(120 miles or 193 km), and largest river in the UK in terms of its
discharge (170m³/sec at Perth), originates in the
highlands and flows down through Strathtay in the center of Scotland,
and then eastwards flowing through Perth and Kinross to the Firth of Tay
and the North Sea. The Tay that drains much of the southern highlands,
has its source high on the slopes of Ben Lui, just 20 miles (32 km) from
the west-coast town of Oban, in Argyll and Bute. Along its course the
river assumes different names, known as the River Connonish for the
first few miles, then River Fillan and River Dochart, until it flows
into Loch Tay at Killin. From Loch Tay the river emerges at Kenmore as
River Tay, and flows down to Perth, which in historical times was the
lowest bridging point of the river. Downstream of Perth the river
becomes tidal and enters the Firth of Tay.
The River Tay where the Abernethy Pearl was
discovered by the pearl fisherman William Abernethy, is a fast-moving
river, with a discharge of 170m³/sec at Perth. The
turbulent waters of this river, with its falls and rapids along the
course of the river from the highlands downstream provides the ideal
habitat for the freshwater pearl mussel Margaritifera margaritifera,
around which a pearl fishing industry was based since ancient times. The
River Tay is also famous for its salmon and trout fishing, two species
of fish that serve as intermediate hosts in the completion of the life
cycle of Margaritifera margaritifera.
Classification of the
freshwater pearl mussel - Margaritifera margaritfera
Kingdom :
Animalia
Phylum :
Mollusca
Class
: Bivalvia
Order
: Unionoidae
Family : Margaritiferidae
Genus :
Margaritifera
Species :
margaritifera
External appearance of the shells of Margritifera
margaritifera
Photo above, Creative Commons
Life History of
Margritifera margaritifera
Growth and
reproduction
The freshwater pearl mussel Margaritifera
margaritifera like all other freshwater bivalves are dioecious, i.e.
their sexes are separate. The growth of the mussels are slow, and they
mature only after 10-15 years. At maturity the length of the mussel
exceeds 6.5 cm (65 mm). The mature males shed sperms into the
surrounding water in early summer from June to July. The sperms enter
the female mussel with the incurrent siphon, and fertilize the eggs,
which develop in a pouch on the gills for several weeks. Larvae formed
in the fertilized eggs known as glochidia measure 0.6 to 0.7 mm, and are
released from July to September. The glochidia resemble tiny mussels,
but their shells are held apart until they encounter a suitable host
like a juvenile Atlantic salmon or brown trout or sea trout, when the
shells snap shut on the hosts gill filaments, thus clinging on to the
gills of the host.
The release of
glochidia and their attachment to a suitable host
The release of glochidia from the females appear to
be a synchronized event taking place over one or two days and influenced
by external factors such as a threshold temperature. Each female release
between 1 to 4 million glochidia, and in any population of mussels
30-60% of the adult females produce glochidia. For a glochidia to
survive it should attach itself to the gills of a suitable host, while
it remains viable, which is usually up to six days. The chances of this
happening during this period is very remote, in the turbulent conditions
of the rivers in which the mussel lives. A majority of the glochidia are
swept away by water currents and perish off. However at least a few of
them find suitable hosts and are able to survive, thus completing the
life cycle. The production of enormous quantities of glochidia is
natures way of ensuring that at least a few them would stand the chance
of clinging on to a suitable host in the turbulent environmental
conditions. The glochidia that successfully attach to the gills of a
host get encysted, where it lives and grows in the hyper-oxygenated
environment, until the following spring.
Glochidia
dropping off from the gills in the following spring and beginning an
independent life
In May or early June, the glochidia drop off from the
gills, and if they land on clean sandy or gravelly substrates they
settle down and begin their independent life. The association between
the glochidia and the fish is not harmful to the fish, but ensures the
survival of the glochidia and enables young mussels to colonize new
areas upstream when the glochidia are dropped after the host fish
reaches these areas. The glochidia that are about a mm in length at the
time they become independent, initially grow quickly reaching a length
of about 4 mm after one year, 12 mm after 3 years, 20 mm after 4 to 5
years and 65 mm at maturity after 10 to 15 years. Thus the average
growth per year of the shell is only about 4 mm per year until the shell
attains maturity. After this growth slows down and the adult mussel
reaches only a maximum of 120 to 150 mm in length in about 80 to 100
years or more. the young mussels are yellowish-brown in color, and as
they attain maturity in 10-15 years they become dark brown or black.
Margaritifera margaritifera- Inner surface of shells
showing thick layers of nacre
Photo above, Creative Commons
Precarious life cycle
of Margaritfera margaritifera that depends on several chance happenings
The life cycle of the freshwater mussels involve huge
losses at different stages, such as sperms not reaching a female mussel,
the glochidia not reaching a suitable host and glochidia not falling on
a suitable substrate from the host. As a result of this precarious life
cycle, any adverse conditions to which the mussels are subjected
to, can only exacerbate the situation, and threaten the survival of the
species. According to Peter Cosgrove, a Scottish-based scientist, an
adult female mussel perhaps produces over 200 million glochidia in her
lifetime to replace just two adults.
Serious decline of
freshwater mussel populations in their holarctic range
The freshwater pearl mussel Margaritifera
margaritifera has a holarctic distribution, which include the northern
temperate regions of the world, extending from the Arctic and the
temperate regions of western Russia, through continental Europe to the
northeastern seaboard of North America. Scientists have found a serious
decline in the populations of this freshwater mussel species throughout
its range, sometimes as high as 95-100%. In many areas of England and
Wales where the species was formerly abundant, populations have declined
seriously or are virtually extinct. In Northern Ireland, home of the
rare hard-water variety of the species known as Margaritifera
margaritifera durrovensis, recent research had shown serious decline in
populations. In Scotland, one of the regions where the species was most
abundant, a recent survey conducted between 1996 and 1999 have shown
that the species is now extinct in most of the lowlands, and generally
scarce everywhere except in a few highland rivers. Studies have further
shown that at the current rates of extinction, the surviving Scottish
populations of margaritifera will be totally extinct in a period of 25
years.
Causes for the
decline in mussel populations
Some of the early causes of decline in populations
were :-
1) Pearl fishing
2) Industrial pollution
Some of the current causes that have been identified
are :-
1) Poor water quality
2) Habitat modification or destruction
3) Decline in host fish population
4) Sedimentation or siltation
5) Eutrophication
6) Acidification
7) Amateur pearl fishing
8) Climatic change
Early causes
1) Pearl fishing
Exploitation of freshwater pearl mussels in Scotland
and other areas in Britain and Ireland had been taking place for
centuries at sustainable levels. However, beginning from the 16th
century onwards commercial exploitation was intensified developing into
a large scale industry in Britain and Ireland. This exploitation was
carried out at unsustainable levels without regard to conservation and
restoration of mussel populations, well into the 19th century, and the
result was the rapid decrease in populations that spelt the doom of the
industry. Restoration of pearl populations to their original levels were
delayed, not only because of the slow growth of the pearl mussels, but
also due to the long time taken for mussels to attain maturity, which
was 10-15 years. In this situation if adult populations that were
still fertile were removed, it had disastrous consequences on the entire
population. However, small scale pearl fishing by individual pearl
divers and the "traveling people" in Scotland continued well into the
20th century, until a total ban was imposed in 1998.
2) Industrial
pollution
The spate of industrialization of the 19th and 20th
centuries had a drastic effect on the environment, with industrial
effluents being discharged into the rivers, and streams, that had a
devastating effect on all aquatic life. In the case of the freshwater pearl
mussels the effect of the industrial pollutants was more serious than in
other species, as mussels were adapted for survival in a highly
oxygenated environment, as found in a fast moving river, with their
rapids and falls. Polluted waters affected the mussel populations in two
ways : 1) By being directly toxic to the mussels 2) By drastically
reducing the oxygen content in the water, which was crucial for their
survival. Industrial pollution eliminated mussel populations in many
rivers, and only those rivers that were untouched by pollution or were
marginally affected were able to sustain such populations.
Current causes
1) Poor water
quality
Poor water quality caused by industrial effluents was
an early cause of declining populations. But now other factors that are
responsible for poor water quality have emerged, such as agricultural
chemicals including chemical fertilizer and pesticides, that find their
way from farms in the catchment areas to the rivers, effluents from fish
farms and chemical sheep dip. These factors not only affect mussel
populations but also host fish populations.
2) Habitat
modification or destruction
Habitat destruction mainly includes river
engineering; the construction of dams for irrigation, hydroelectric
schemes, and flood protection. The impounding of the rivers prevent the
movement of migratory host fish upstream, and disrupts the life cycle of
the mussels. Habitat modification measures include drainage schemes,
flow regulation and fisheries management.
3) Decline in host
fish population
The presence of host fish is crucial for the
completion of the life cycle of freshwater mussels. The decline in the
populations of host fish such as brown trout, sea trout and the
migratory salmonids caused by dam construction, or by the increase of
chemical pollutants in the water, has a direct impact on the mussel
populations, as the larvae that are not able to find a host fish soon
perish off. This has an effect on the recruitment of young mussels to
the population.
4) Sedimentation
or siltation
Poor land management in the catchment areas, such a
overgrazing and poor agricultural practices lead to soil erosion, which
is eventually washed into the rivers and streams and result in siltation
or sedimentation of rivers, altering the habitat of the freshwater
mussels.
5) Eutrophication
Nutrient enrichment of waters by agricultural
fertilizers, mainly phosphorus-containing chemicals, erosion of soil
containing nutrients, release of sewage effluents, urban storm water
runoff etc. can lead to excessive plant growth, mainly phytoplankton
known as an "algal bloom" in bodies of water such as lakes, estuaries,
and slow moving rivers and streams; a phenomenon known as eutrophication.
Eutrophication leads to a decrease in dissolved oxygen in the water,
caused by the decomposition of dead plant material, that can be
catastrophic to both the mussels and the host fish. However, in fast
moving rivers the threat posed by eutrophication is minimal.
Eutrophication has already eliminated mussel populations in southern and
eastern Scotland.
6) Acidification
Acidification of waters can have a detrimental effect
on mussel populations. Acidification can be caused by chemical
effluents, and decomposition of plant material. The planting of
Coniferous trees in the catchment area, leads to acidification of the
soil by microbial decomposition, and these acids can can eventually be
drained into the rivers.
7) Amateur pearl
fishing
Amateur pearl fishing aided by improved accessibility
to the upper reaches of rivers have resulted in the wanton destruction
of mussel populations, just to try their luck in finding the elusive
pearl. The freshwater mussel species Margaritifera margaritifera is not
edible. Thus their destruction just for the sake of an occasional pearl
is morally unacceptable. The use of tongs to open the mussels and
returning them to the water after searching for pearls, unharmed, is
highly commendable, but not practiced by pearl hunters.
8) Climate change
Recent climatic changes, with changes in rainfall
patterns, resulting in heavier rains, has washed away many of the sand
beds in the rivers, the potential areas where young mussels mature. This
could have serious implications for the recruitment of young mussels to
the populations of freshwater mussels.
Scotland bans the
fishing of freshwater mussels in 1998
Dr. Mark Young, an Aberdeen University biologist and
freshwater mussel expert is of the opinion that only about a dozen
Scottish rivers were now home to the shellfish, compared with nearly a
160 a century ago. Based on the studies of research scientists both in
Scotland and the European Union, that painted a bleak picture of the
status of the freshwater mussels in Scotland, which according to one
report was threatened with total extinction in a period of 25 years, the
Scottish Executive declared in 1998, that the freshwater mussel was a
protected species under schedule 5 of the Wildlife and Countryside Act
of 1981. The law promulgated under the act states that :- "It is an
offence to kill, injure, take, intentionally disturb, or damage their
habitat, or sell, offer or expose for sale, advertise for sale and
transport for sale any freshwater pearl mussel or its pearls without a
license from the Scottish Executive. A license issued by the Scottish
Executive only permits the sale of pearls obtained prior to 1998.
Illegal sales of freshwater pearls carry a penalty of up to six months
imprisonment and a maximum fine of £5,000. The
enforcement of the law was vested with the Scottish Natural Heritage (SNH)
and the police. Since the introduction of the law the SNH has been
working with the jewelers to raise awareness among the people, and with
the police to track down those breaking the law.
Dr Mark Young- research scientist from Aberdeen
University involved in the conservation of the freshwater mussel in
Scotland.
National Species Action Plan introduced by the Scottish Natural Heritage
to restore mussel populations
Having introduced legislation to
eliminate one of the main threats to surviving mussel populations, viz.
pearl fishing, the Scottish Natural Heritage together with institutions
such as the University of Aberdeen, the UK Biodiversity Steering Group
and the European Union have drawn up a National Species Action Plan, to
encourage measures to save the freshwater pearl mussels from total
extinction. The objectives and targets of this action plan are :- 1)
Maintaining the size of all viable populations 2) Increasing the
size of all viable populations 3) Encouraging the re-colonization
of the species in at least 10 suitable former areas by 2005.
The plan also envisages remedial
steps to eliminate the causes identified above, that led to the decline
in mussel populations.
The
present owners of the Abernethy Pearl
After the discovery of the
Abernethy Pearl (Little Willie Pearl) in 1967 in the River Tay, by
William Abernethy, the professional pearl diver, the pearl was sold for
an undisclosed sum to the owners of Cairncross Jewelers in Perth.
Cairncross Jewelers placed the Abernethy Pearl on permanent display in
their stores, and since then have been viewed by innumerable visitors
from the UK and abroad. The pearl was still on display at Cairncross
Jewelers in 2006, according to the BBC program "This Week" titled "The
Cairngorms" aired on Saturday, August 19, 2006, and also according
visitors reports published on the web in 2007. Thus the reports carried
by most websites that the Abernethy Pearl was sold in 1992, after almost
30 years of display at Cairncross jewelers appear to be baseless.
Caincross Jewelers is one of only two jewelers that have been granted a
license by the SNH to sell pearls and pearl-studded jewelry sourced
before 1998, the year the new laws controlling pearling in Scotland
became effective.
You are welcome to discuss this post/related topics with Dr Shihaan and other experts from around the world in our FORUMS (forums.internetstones.com)
Related :-
1)
Survival Pearl
2)
Paterson Pearl or Queen Pearl
External Links :-
1)
Ecology of the Freshwater Pearl Mussel - Ann
Skinner, Mark Young and Lee Hastie.
References :-
1) Pearl Luster - www.pearl-guide,com
2) Pearl Value Factors - Judging and Evaluating
Pearls - Amy Hourigan, www.bellaonline.com
3) River Tay - From Wikipedia, the free encyclopedia
4) The Book of the Pearl - George Fredrick Kunz
5) Eutrophication - From Wikipedia, the free
encyclopedia
6) Ecology of the Freshwater Pearl Mussel. Conserving
Natura 2000 Rivers Ecology Series No.2 English Nature, Peterborough. -
Ann Skinner, Mark Young and Lee Hastie.
7) Freshwater pearls mussel their way back into gem
shop - by Angie Brown, article published in "The Scotsman" of June 23,
2004.
8) Action Plan for Margaritifera margaritifera -
Biodiversity - The UK Steering Group Report - Volume II, Action Plans
(December 1995, Tranche I, Vol 2, p 162)
9) Freshwater Pearl Mussel - From Wikipedia, the free
encyclopedia
10) The Cairngorms - This Week, Saturday August 19,
2006. www.bbc.co.uk
