On one hand, it is traditional. One the other, they are a rapacious culture (now far exceeded by the Chinese). There must be traditional or cultural reasons by I am no expert on these. I vaguely recall an explanation that had to do with their religious beliefs vis a vis eternity and conservation.
It has always disturbed me that the last breeding pair of any species of pretty much anything edible will cause a bidding war in most of Asia.
Put at least they are not being allowed to hunt them to extinction like they can with many type of fish. Not to mention the rhinos, tigers, several types of rare deer, several species of bears, snow leopards and elephants. Somebody send these people some Cialis, please.
Uh, that whole last bit was not aimed at the Japanese. They mostly just rape the sea - but they do it world wide.