The Japanese Horseshoe Crab
The scientific name of
the Japanese horseshoe crab is Tachypleus tridentatus. Horesehoe
crabs live in Saga Prefecture in Kyushu (Southern Japan), Okayama,
and Ehime Prefecture. At one time there were a lot of horseshoe crabs around
the Seto Inland Sea and northern Hyushu in
Japan. Now they are considered endangered, and this species of horseshoe
crab is considered a national treasure. Much of the area where the horseshoe
crab laid its eggs every spring has been destroyed because of water pollution,
and the population is increasing, and people are building dikes and filling
in beaches so they can have more land. For example, at one time there were
many horseshoe crabs along a tidal flat along Kasaoka Bay
in Kasaoka. In fact, this area had been set aside as a protective zone
for horseshoe crabs by the Japanese government. Then in 1966 a land reclamation
project covering over 1,811 hectares in the bay was begun. The project,
which was completed in 1990, was one of the largest of its kind in Japan.
It was supposed to create more land for houses and farming. It did create
more land, but it also completely destroyed the entire population of crabs
in that area.
After that project, in 1975 the government
established the Horseshoe Crab Protection Center. Then when
they realized the horseshoe crab was in danger of becoming extinct, it
turned the center into the The
Kasaoka City Horseshoe Crab Museum. In
1993 the people at the museum began a five year project to raise horseshoe
crabs from eggs which they would then release into the bay. They were hoping
this would increase the number of horseshoe crabs in the bay. How
successful they have been they are still not sure. However, they have learned
some interesting things while they have been working on this project. For
example, "the crab can survive without any food for up to two years and
can survive in a dry environment for up to two weeks as long as its respiratory
organs remain wet."
At the present time it is estimated
that only 2,000 - 4000 horseshoe crabs still remain in Japan. Places
where you once saw lots of horseshoe crabs mating, now it is rare to see
one pair of crabs. (The horseshoe crabs in Japan are different than the
ones in Delaware Bay. The crabs in Japan mate for life.) So, there's much
work to be done.
Students in Japanese schools study
about horseshoe crabs. We have been corresponding with Miyo
Elementary School of Koriyama city. Mr. Hagawa told us the fourth grade
students there have been studying about how to save the horseshoe crab.
He sent us pictures of the students doing environmental studies.He
also sent us materials they use in their study of the environment.
He even sent us an 80 page book about the horseshoe
crab with some wonderful illustrations.
Students at Imari High School have been studying
horseshoe crabs for ten years. If you go to the school's home page
you will see pictures
and a description of what they have been doing. They have tanks of
horseshoe crabs of various ages which they observe. They have found that
Japanese horseshoe crabs mate from the middle of June until the beginning
of August. A pair of crabs come to shore on high tide when it is a full
moon. The female, which is bigger than the male, lays a couple hundred
eggs in about ten different places. Forty-five days later the eggs hatch,
and the baby crabs go where the water is shallow. There they eat plankton.
As they get bigger they molt. The male molts about sixteen times in his
life. The female molts about seventeen times. The crabs live to be about
fifteen years old. Nearby there is an area where horseshoe crabs mate.
The students and people from the community get together in June and clean
that area before it's time for the crabs to mate. Many people in Japan
are concerned about the future of the horseshoe crab and are doing whatever
they can to see that it survives. A Japanese scientist
sent us some pictures and a description of what he is doing.
If you would like to make a Japanese horseshoe
crab, Mr. Toru Nakashima, from Kasaoka, sent us a
pattern of a horseshoe crab.
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