Origin of Name
The name refers to the extraordinary nine-stranded
pearl bracelet composed of Biwa pearls, that drew international
attention after its exposition as part of an international traveling
exhibition organized by the American Museum of Natural History, in
collaboration with the Chicago Field Museum, known as "Pearls : A
Natural History," which was hosted for the first time in October 2001 by
the American Museum of Natural History, New York, and subsequently by
other museums in the United States and countries like Canada, France,
Japan, Australia, and the United Arab Emirates. The Biwa Pearl Bracelet
that belongs to Jill Gindoff Cashman was given on loan to the
American Museum of Natural History for the purpose of the exhibition. "Biwa
pearls" refer to freshwater pearls cultured inside a species of
freshwater mussel found in the Biwa Lake in Japan, which incidentally
was the first pearls to be cultured inside freshwater mussels, and hence
the name "Biwa Pearls" at one time came to be synonymous with all
freshwater pearls irrespective of their origin.
The Biwa Pearl Bracelet
©Australian Museum
Characteristics of
the bracelet
The Biwa Pearl Bracelet that belongs to Jill Gindoff
Cashman, was designed in the 1950s at New York, and is made up of
cultured Biwa pearls and gold. The bracelet is made up of nine cultured
Biwa pearl strands, each strand consisting of an average of 20 pearls.
The pearls have the characteristic features of Biwa pearls, being
non-nucleated cultured pearls almost entirely made of nacre, and having
the luster and brilliance of natural saltwater pearls. They are small
having the average size of about 5-6 mm, the normal size of Biwa pearls
produced during this period. Most of the pearls are irregular in shape,
another characteristic of tissue nucleated Biwa pearls. However a
multitude of other shapes can also be recognized out of the
approximately 180 pearls in the bracelet, such as rounds, near-rounds,
ovals, drops, buttons, triangles, rectangles, quadrilaterals etc.
The nine strands of the bracelet extend from the
circular gold work studded with six spherical Biwa pearls, at one end to
the clasp at the other end. When the bracelet is tied around the wrist,
the clasp will fit in below the circular gold work, which forms the
centerpiece of the bracelet.
Shape of Biwa pearls
Biwa peals are generally irregular (baroque) in
shape, but they also exist in a variety of different shapes such as
rounded, near-round, button, oval, elongated (dogtooth), flat, grain etc.
By varying the size and shape of the mantle tissues implants, it was
possible to produce sometimes bizarre fancy shapes, such as bars, double
bars, cross-over bars, crosses, dragons, sticks, buttons, triangles,
butterflies, shapes with a jagged outline, letters of the alphabet, etc.
Size of Biwa pearls
The pearls are small with an average diameter of
about 5-6 mm. This is associated with the short period of growth after
implantation, which is 1-2 years.
Color of Biwa pearls
The color and luster of Biwa pearls, said to be
identical or surpassing that of natural saltwater pearls, is clearly
associated with their all nacre body free of nuclei. The common colors
of Biwa pearls are white, pink and orange. Apart from this they also
occur in fancy colors, such as lilac, wine, green and blue, and colors
such as cream, silver, brown and gray.
Luster of Biwa pearls
Luster of a pearl which is its reflective property is
also associated with the thickness of the nacre. Thus Biwa pearls being
all nacre undoubtedly has an extraordinary nacre that rivals that of
natural saltwater pearls.
History of Biwa
Pearls
Mikimoto's success in
culturing saltwater pearls
In the year 1916, Mikimoto who had been doing
extensive research on culturing spherical saltwater pearls since 1888,
finally adopted the "Mise-Nishikawa" method of culturing spherical
pearls, and successfully cultured several spherical saltwater pearls
using the saltwater oyster species Pinctada martensii. The method that
involved the insertion of a piece of mantle tissue together with the
shell nucleus into the oysters mantle or body, was found to be commercially
viable, and resulted in a major breakthrough for the Japanese cultured
pearl industry. By the year 1935, Japan had 350 pearl farms producing 10
million cultured pearls annually.
Fujita's attempts at
culturing freshwater pearls applying the same techniques perfected for
saltwater pearls
Following the successful culturing of salt water
pearls using the "Mise-Nishikawa" method, attention was diverted towards
the culturing of freshwater pearls inside freshwater mussel species,
found abundantly in the lakes and rivers of Japan. In the year 1928,
Dr. Masao Fujita, a friend and associate of both Mikimoto and Nishikawa, made the
first attempt to culture whole freshwater pearls inside a common
freshwater mussel species Hyriopsis schelegi, found in the largest
and most ancient
freshwater lake in Japan, Lake Biwa, situated about 10 km north of
Kyoto, in the Shiga Prefecture. Lake Biwa-ko is fed by a multitude of
rivers that originate in the surrounding mountains of Hira, Ibuki and
Suzuka. Fujita adopted the same "Mise-Nishikawa" technique that was
successfully applied in the culturing of saltwater pearls. However, the
results obtained were not so encouraging. Fujita and his co-worker
Yoshida were undeterred, and continued research into the culturing of
freshwater pearls throughout the 1930s, and achieved limited success in
culturing sub-standard bead nucleated pearls. Several thousand pearls
were harvested by Fujita, and these early Biwa pearls were almost
universally elongated and baroque. The pearls were also quite small,
with an average size of about 5 mm. Dr. Fujita sold almost all his pearl
harvest to the Mikimoto's Tokyo pearl store.
Lake Biwa from outer space
Photo Above Creative Commons
Seiishiro Udo and
Keisaburo Sakiyoshi perfect the technique of culturing non-nucleated
freshwater pearls, that came to be known as Biwa pearls
Dr. Fujita and
Yoshida made an accidental but very significant discovery during their
research work, viz. that mantle tissue accidentally implanted in this
mussel could initiate pearl growth. Unfortunately, they did not pursue
this research further, and it was left to two other research workers, Seiishiro Udo and Keisaburo Sakiyoshi, who beginning from the year 1945,
experimented with freshwater pearl culture using the freshwater mussel
Hyriopsis schelegi and perfected the technique of non-nucleated
pearl production, using mantle tissue only. Their research was carried
out in the Hirako reservoir, a dammed arm of Lake Biwa, near the village
of Shina. Their efforts were successful only in the early 1960s, and
they formed the Shinko Pearl Company, who were the first commercial
producers of freshwater pearls, that came to be known as Biwa Pearls.
Lake Biwa and the city of Otsu
Photo
Above-Free Art Licence
Culturing of
non-nucleated freshwater pearls in Lake Kasumigaura and Lake Gifu
While extensive culturing of non-nucleated freshwater
pearls using the freshwater mussel species Hyriopsis schlegeli began in
the early 1960s in the Lake Biwa, almost simultaneously culturing was
also carried out in two other lakes, Kasumigaura in Ibaraki Prefecture,
70 km northeast of Tokyo, and Gifu near Lake Biwa to the north of
Nagoya. In the case of Lake Kasumigaura, the second largest lake in
Japan, Hyriopsis schlegeli which was not native to the lake, was
transferred from Lake Biwa during the 1930s, and a significant
population established by the 1950s. When the culture of mantle grafted
freshwater pearls began in the early 1960s in the Biwa Lake, commercial
cultivation of Biwa pearls also began in Lake Kasumigaura in 1963, with
around 180,000 mussels being harvested and implanted during that year.
Catastrophic decline
in production of Biwa pearls after 1980, caused by multiple factors
By the year 1970, the total production of
tissue-grafted freshwater pearls from Lake Biwa and other secondary
sources, reached an all time high of 6.3 tons, the highest ever achieved
for Biwa pearls. Production declined rapidly thereafter due to
devastating environmental pollution of the lakes caused by industrial
effluents and agricultural pollutants reaching the lakes through their
feeder rivers and streams, which was detrimental to the mussel
populations. Apart from this habitat loss, over fishing and invasion of
exotic species of fish that threatened the survival of the host fish for
the gloichidia, also contributed to the rapid decline in population of
mussels. and In the year 1998, the total production of Japanese
mantle-grafted Biwa freshwater pearls was only 214 kg.
Attempts made by
pearl farmers to overcome the problem of pollution
It appeared that the early developmental stages of
the Hyriopsis mussels were more susceptible to environmental pollutants
than the adult mussels. Thus pearl farmers resorted to cultivating
spat-bred Hyriopsis schlegeli in artificial freshwater ponds, and
implanting them after the mussels had reached adulthood. The implanted
mussels were eventually returned to the polluted freshwater lakes, and
left for the stipulated grow out period. The results obtained were only
partially successful.
Some of the desperate pearl farmers who were not able
to cope with the pollution problems relocated to China, a vast country
where a multitude of pollution-free freshwater bodies were
available for successful pearl cultivation. They based their
non-nucleated freshwater pearl culturing on the local mussel species
found in China known as Hyriopsis cumingii.
Another strategy adopted by scientists and pearl
farmers in overcoming the problem was the introduction of a hybrid pearl
mussel, created by crossing the Japanese pearl mussel, Hyriopsis
schlegeli with the Chinese pearl mussel, Hyriopsis cumingi, to the
freshwater lakes where pollution was relatively less, such as the Lake
Kasumigaura.
Lake Kasumigaura
Cultivation of
freshwater pearls in the Lake Kasumigaura
Culturing of non-nucleated freshwater Biwa pearls in
the Lake Kasumigaura started in 1963, but soon production declined
rapidly due to over exploitation, pollution and eutrophication, and
almost completely ceased in the early 1980s. With a view of reviving the
industry pearl farmers developed a hybrid variety between the Japanese
and Chinese freshwater mussels (Hyriopsis schlegeli/Hyriopsis cumingi),
and introduced it in the Lake Kasumigaura, the least polluted of the
lakes in Japan. The new hybrid variety of freshwater mussel was said to
be somewhat resistant to pollution, and were also able to accept a round
nucleus. In 1993, the first crop of experimental pearls were produced
and their quality rivaled that of the famous Biwa pearls, with a
beautiful luster and highly desirable color in different shades of rose
pink, purple, white and cream. The cultivation period of the "Kasumiga
pearls" was four years, the longest for any cultivated pearl. Thus the
first marketable crop of "Kasumiga pearls" were produced only in 1997,
four years after the first experimental crop. The high quality of
Kasumiga pearls is necessarily associated with the thickness of its
nacre, which should be considerable given the long period of growth of
the pearl. The extraordinary color and luster of the pearls are
undoubtedly associated with the thickness of the nacre. The size of the
pearls are also large varying from 11-16 mm. Thus the combination of
desirable color, luster and size have made "Kasumiga pearls" one of the
most sought after pearls in the world.
Lake Kasumigaura- satellite photo
Multiple implantation
of Hyriopsis schlegeli
A significant difference between saltwater pearl
culturing and freshwater pearl culturing is that while in the former the
saltwater oyster is usually implanted only with a single bead nucleus,
in the latter the freshwater mussel is implanted with multiple tissue
nuclei, sometimes as high as forty implantations per mussel. This
explains why the Chinese cultured pearl industry based on the freshwater
mussel species Hyriopsis cumingi, has overtaken all other cultured pearl
industries in the world, within a short period of time.
In Japan in the culturing of Biwa pearls, initially
the mussel species, Hyriopsis schlegeli was grafted with 21
implants of mantle tissue :- five inside the body and eight on each side
of the mantle. This method, especially implantation inside the body,
needed special technical skills, and therefore was replaced by the
present standard implantation technique, that makes use of only the
mantle on both sides of the valves, for implantation. In this technique
forty pieces of mantle tissue, from a sacrificial mussel, is implanted
in two rows of ten, on each side of the mantle. The implanted mussel is
returned to its natural aquatic environment and left for around two
years, the usual grow out period for the cultured Biwa pearls.
The use of the term
Biwa pearls
Initially the term Biwa pearls was used only for
freshwater pearls cultured from the mussel species Hyriopsis schlegeli
in the Biwa Lake, the largest and most ancient lake in Japan. Later the
term was extended to include freshwater pearls cultured from the same
species in other lakes such as Kasumigaura and Gifu. Eventually the term
was used for all freshwater pearls produced in Japan irrespective of
their origins. Biwa pearls were the first freshwater pearls to be
cultured in a freshwater mussel, and received world wide recognition and
acceptance. Thus the term Biwa pearls became synonymous with all
freshwater pearls irrespective of the country of origin. In the United
States the use of the term Biwa Pearls is restricted only to freshwater
pearls originating in the Biwa Lake of Japan. The use of the term to
refer to freshwater pearls from other sources in Japan or from other
countries is illegal.
Close up of some Lake Biwa Pearls
The freshwater mussel
Hyriopsis schlegeli
Classification of
Hyriopsis schlegeli (Martens 1861)
Kingdom
: Animalia
Phylum
: Mollusca
Class
: Bivalvia
Sub-Class :
Palaeoheterodonta
Order
: Unionoida
Super-Family :
Unionoideae
Family
: Unionidae
Genus
: Hyriopsis
species
: schlegeli
Common names : Ikecyo-Gai
(Japanese)
Biwa Pearly Mussel
Reproduction in
Hyriopsis schlegeli
In freshwater mussels the sexes are separate. Mature
male mussels release sperms into the surrounding water, some of which
may be drawn into the female mussel through the incurrent siphon. The
female's eggs are located in the water tubes of the gills, where they
get fertilized by the incoming sperms and develop into glochidia, the
larval form of the mussel. The glochidia are not fully developed and its
further development depends on whether it can attach itself successfully
to the gills or fins of a suitable host fish after being released by the
female mussel. In the case of Hyriopsis schlegeli out of the several
fish species found in Lake Biwa, that has been identified as hosts
for the glochidia, one example is "trident goby" (Tridentiger kuroiwae).
The glochidia encyst on the gill filaments, where they metamorphose into
juvenile mussels. The time taken for the transformation into juvenile
mussels depends on several factors including water temperature, and can
vary from a few days to several weeks. The juvenile mussels drop off the
gills or fins of the host fish, and if they fall on a suitable habitat,
they will grow and develop into adults to continue the life cycle.
The Biwa pearl mussel is a large, slow growing,
phytoplankton-feeding, freshwater mussel taking around 6-7 years to
attain full maturity. The size of the shell gives an indication of the
state of maturity of the mussel. Mussels are fully matured when the size
of the shell is 70 mm (7 cm). However a fully grown Biwa pearl mussel
can attain a size of up to 13-16 cm. The mussels are long lived and if
left undisturbed can live up to the age of over 40 years. The
external surface of the mussel is dark greenish-brown in color. The
internal surface of the valves are coated with high-quality lustrous
nacre. Depending on the season of the year, these mussels could lie
either partly or fully embedded in the sand and mud on the bottom of the
lake.
Was environmental
pollution the only reason for the collapse of the Biwa cultured pearl
industry ?
The Biwa Pearly Mussel is a species of Unionidae
mussels endemic to the Lake Biwa and its satellite lakes, in the Shiga
prefecture of Japan. The lake was also host to many endemic fish
species, that served as hosts to the glochidia larvae of the pearl
mussels, which was crucial for the completion of their life cycle. The
mussel is long lived with a life span of over 40 years, and was the
first freshwater mussel in the world to be exploited for artificial
pearl culture. The human population that inhabited the immediate
surroundings of the lake was 1.3 million.
The Biwa pearly mussels were harvested and the mature
mussels (shell size greater than 7 cm) were tissue implanted before
returning to the water to begin the culturing process, that lasted from
1 to 2 years. In the early 1970s the catch of mussels were over 10
metric tons (10,000 kg), which was maintained with minor fluctuations
until the early 1980s, after which production decreased
drastically to less than one metric ton in the mid-1980s, less than 100
kg in 1990 and collapsed completely in 1992. With the collapse of the
mussel harvests the cultured pearl industry based on the Biwa pearly
mussel also totally collapsed.
Environmental degradation was found to be the main
factor responsible for the wiping out of mussel populations in the lake,
caused by industrial effluents and agricultural chemicals finding their
way into the lake through the multitude of rivers flowing into the lake
from the surrounding hills. The chemical pollutants were more
detrimental towards the early developmental stages of the mussels, such
as the glochidia larvae, the juvenile mussels, and the immature mussels
less than 6-7 years old, and with a shell length of less than 7 cm. This
had a devastating effect on the population of adult mussels suitable for
implantation.
However, apart from environmental degradation other
contributory factors have also been identified, that was responsible for
the collapse of the industry. Some of these factors are :- 1) Habitat
loss 2) Eutrophication 3) Overfishing 4)
Invasion of exotic species
1) Habitat Loss
The Biwa pearly mussels live in the bottom of the
lake, either partly or fully embedded in the sand and mud. Various
regions of the lake have been subjected to dredging periodically, and
this resulted in the loss of habitat for bottom dwellers of the lake,
mainly the freshwater mussels. One region that was dredged
thoroughly with a serious loss of habitat for the mussels was the south
basin of the lake.
2) Eutrophication
Sections of the Lake had been subjected to
eutrophication from time to time, that was detrimental to other aquatic
organisms living in the lake, such as fishes, and mussels.
Eutrophication results when the lake receives excess nutrients such as
fertilizers from surrounding agricultural fields, discharges from sewage
treatment plants and soil nutrients by erosion. Excess nutrients
stimulate excessive plant growth, such as algae and aquatic weeds, often
known as an algal bloom. The algal bloom itself is not detrimental to
other living organisms; however, when dead plant material decompose the
concentration of dissolved oxygen in the water is drastically reduced,
causing the death of other living organisms in the water, like fishes
and mussels.
3) Overfishing
Continuous over harvesting of mussels from the early
1970s to 1980s, that resulted in a catch of 10 metric tons annually,
coupled with the slow growth rate and recruitment of mussels, caused a
drastic decline in the adult populations of the mussel. Given the fact
that the mussels took 6-7 years to attain maturity, the continuous
harvesting of adult mussels, without giving sufficient time for the
younger ones to regenerate had a devastating effect on the population.
4) Invasion of exotic
species
The introduction of exotic species into the lake was
also a contributory factor. In the 1960s the fish known as blue gill (Lepomis
macrochirus) was introduced into Japanese lakes. While being a source of
food, the blue gill was also expected to be a suitable host for the
glochidium larvae of the Biwa pearly mussel. However, contrary to
expectations the blue gill instead of becoming a host fish to the
glochidium larvae, threatened the existence of many native host fishes
of the Biwa pearly mussel in the 1980s. Exotic fishes could threaten the
native fishes by being more aggressive, and competing for the same
source of food.
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
External Links :-
1) Extinction Risk Analysis in Long-lived
Invertebrates - Hiroyuki Matsuda, Ocean Research Institute, University
of Tokyo.
References :-
1) Gems - Michael O'Donoghue and Robert Webster
2) Extinction Risk Analysis in Long-lived
Invertebrates - Hiroyuki Matsuda, Ocean Research Institute, University
of Tokyo
3) Pearl - From Wikipedia, the free encyclopedia
4) Japanese Pearl Farms - Akoya, Biwa and Keshi
Pearls,
www. allaboutgemstones. com
5) Freshwater Pearls, Biwa Pearl Mussel, Hyriopsis
schlegeli - American Museum of Natural History,
www.amnh.org
6) Kasumiga Pearls -
www.pearls.com
7) Pearl -
www.geo.utexas.edu
8) Pearls, opulence and obsession - website of the
Australian Museum
