What's Killing the Oysters?
For decades, oyster farmers in Ago Bay, Japan, had
everything to smile about, but recently the tide has turned.
by Peter Tyson
Japan's akoya oysters have been preëminent among cultured pearls
ever since Kokichi Mikimoto first established the industry in the early part of
this century. But since 1994, something has been killing off the
akoyas of Ago Bay, the heart of Japan's cultured-pearl business, and elsewhere
in the country.
Experts attribute the initial oyster deaths in 1994 to "red tide," a bloom of
microscopic, toxin-producing animals in the ocean that proved deadly to the
oysters. Named for the discolored water created by the presence of the minute
creatures, red tides are short-lived events. Yet the oyster deaths continued
long after the 1994 tide had dissipated; in fact, they increased. In 1996, the
most recent year for which figures are available, 150 million akoya oysters
perished, according to Devin Macnow, executive director of the Cultured Pearl
Information Center, a trade group in New York City financed by the Japan Pearl
In the wake of the die-off, pearl production has taken a beating. Japanese
pearl farmers reaped only 56.6 tons of akoya-grown pearls in 1996, down 22
percent from the 1993 harvest. Currently, production is just a quarter of what
it was in 1995. Pearl buyers around the world have witnessed a shortage of the
most desirable akoya pearls, especially those in the 6 and 7 millimeter size
range and larger. The dearth of akoyas has helped open the door for other kinds of pearls,
such as Chinese freshwater and South Seas saltwater pearls, with a consequent
loss of market share for the long-reigning akoyas. "I compare it to what
happened to General Motors," says Richard Torrey, editor of Pearl World, an
international pearling newsletter based in Phoenix, Arizona. "The Japanese have
just had to accept a much smaller market share than they've been accustomed
The harvest of akoya pearls such as these raised in Ago Bay has
mysteriously plummeted in recent years.
A Gem of an Enigma
Even after several years of scientific investigation, the specific cause of the disease
remains a mystery. The illness first makes itself known when the abductor
muscle, which holds the two parts of the oyster shell together, turns a
reddish-brown. Ultimately, eight out of ten affected oysters die from the
affliction, which so far has only affected akoya oysters. Even isolating
apparently healthy oysters has had no effect: the disease seems to ferret them
Government and company researchers both within and outside of Japan have
struggled to identify a specific pathogenic source. "We haven't been able to isolate any
virus, at least at our lab here," Dr. Toshihiko Matsusato, a pathologist at
Japan's National Research Institute of Aquaculture, told the Associated Press
in August 1998. "It could even be something totally unknown." Scientists and
others have suggested everything from inbreeding to climate change as possible
causes. The most prevalent notion is that the culprit is a virus.
Pearl farmers haul out their oyster cages in Ago Bay.
Many remain skeptical of the virus theory, however. "To me, the problem has
always been extraordinarily simple: it's pollution," says Fred Ward, a
gemologist and author of a book on pearls (see History of Pearls and
Culture of Freshwater Pearls). "I would never attribute it to an
unidentified mystery disease. It's a multitude of pollution-related problems."
When Kokichi Mikimoto first began growing oysters in Ago Bay early in this
century, he says, the bay was close to pristine, with few people living around
it and no industry. Today, however, the heavily populated bay faces a
continuous assault, he says, from industrial and automobile pollution,
pesticides and herbicides, household detergents and other chemicals, even raw
sewage. "Until you eliminate those and give it a chance to recover, there's no
hope," Ward concludes.
Others feel the oyster farmers themselves might be to blame. "The Japanese
have always tended to place too many oysters too close together," wrote Andy
Müller in the December 1996/January 1997 issue of Pearl World. "In
earlier days (when sea conditions were better), most oysters still had a fair
chance to survive in their densely packed state. But today's equation of high
pollution, plus high shell density, just doesn't work out. It takes just a
little change in either condition to trigger high mortality in oysters . . .
even in a species as hardy as the akoya."
Ago Bay alone harbors an
estimated 130 akoya-oyster farmers.
Macnow, for one, takes issue with the idea that pollution is to blame. For one
thing, he notes, akoya oysters share the same waters with other Japanese
aquaculture products, including shrimp, other oysters, and fugu, or
blowfish, which is highly sought after for sashimi, the Japanese dish of thinly
sliced raw fish. "If there was a significant amount of pollution," he says,
"this would have hit the other industries, which so far have not been
affected." He also notes that 20 percent of those oysters that get the disease
survive and go on to produce a decent pearl.
In the wake of falling harvests, akoya oysters
may get a bit of breathing room.
Whether the cause is a natural virus, a pollution-caused disease, or something
entirely different, the Japanese have to come up with something fast to save
the akoya oyster. According to Torrey, Japanese scientists claim that they
recently isolated the virus. They believe it cannot travel more than 330 feet
underwater, and so to combat its spread, they plan to thin the densities of
akoya oysters in afflicted areas. Eventually, they maintain, akoya oyster
populations should return to health, probably by the year 2002. Thinning may
solve the problem, Müller says, because lower shell density usually
results in a higher quality pearl. "In effect, the farmers will be getting more
with less," he says.
Others feel more radical solutions are required. Ward advocates moving oyster
farmers out of the hardest-hit areas, such as Ago Bay, even as he concedes that
few clean bays remain in Japan in which to relocate the farmers. Even without
the disease, he says, the estimated 130 pearl farmers currently vying for space
within the bay would represent an enormous strain on the system.
"The Japanese are perfectly capable of taking care of their coastlines and
bays," says Torrey, who lived and worked in Japan for 13 years. "But it's the
Japanese nature to bury their heads, like ostriches. They have a saying that,
in translation, means 'can't be helped.' It's fate."
Will Japan become a nation of pearl processors and marketers rather than
producers? Only time will tell.
If so, it is conceivable that the preëminence of akoyas is over. Indeed,
Torrey says it's possible the Japanese akoya industry may never recover to what
it was in Mikimoto's heyday. "Many people believe the Japanese will become more
processors and marketers of pearls than producers," he says, "while
concentrating only on producing higher-quality, large-sized akoyas."
Peter Tyson is Online Producer of NOVA.
What's Killing the Oysters |
Culture of Freshwater Pearls
How Many Pearls? |
History of Pearls |
Teacher's Guide |
Site Map |
Editor's Picks |
Previous Sites |
Join Us/E-mail |
About NOVA |
Site Map |
PBS Online |
NOVA Online |
© | Updated November 2000