Since around 1994, mass mortality in conjunction
with the reddening of adductors in mother pearl oysters (Pinctada fucata martensii) began locally in a few
marine areas of Japan where pearl oysters are produced,
but in the three years from 1996 to 1998 the die-offs
spread to all the main pearl-producing prefectures in
western Japan. Pearl production in 1999 was less than
25 t, only about one-third of that produced in the first
half of the 1990s when production was the highest. This
was a serious blow to Japan's pearl industry. Since then
the pearl oyster mortality rate has lessened somewhat,
but scientists have yet to determine the cause of red
adductor disease or develop an effective way to combat
it. Pearl production is still low and there are concerns
about declining quality