Dear Frank,

Marine molluscan resources on Okinawa have been subjected to intensive exploitation or over-harvesting
after you were enjoying reef walks at low tides only a couple of decades ago. When the locals collected
shells for home consumption during low tide periods, these molluscan populations had plenty time for
restocking by themselves. Things are all different now, because professional fishers use diving gears and
other advanced means of exploitation such as an underwater torch (that can make the whole sea bottoms
visible around the divers for easy catch of nocturnally active species). Once the brood-stocks were decimated
it is very hard for reef dwellers to come back. There have been government-funded projects to restock these
molluscs (giant clams, green snail and trochus), but it takes a long looong time to get them increased and
to be self-propagating. The small giant clam (T. crocea) restocking project was initiated in the early 1970s
and juveniles produced in the government hatcheries have been planted on the reefs in many hundred of
thousands so far, but the recovery is very slow. The trochus project followed and juvenile releases have
been underway but we must wait for several years to see the results, as they grow to maturity very slowly.
The green snail project is the most recent since its life cycle was not known until the late 1980s. Juvenile
mass-production has been established for this snail and releasing methods are under investigation.
It is so easy to destroy molluscan stocks of commercial value but very hard to restore after destruction.

Masashi Yamaguchi
Univ. of the Ryukyus,
on Okinawa