Masashi,

I agree, large conspicuous adults could be over-collected and the population
decimated (which really means only a tenth is destroyed but has become
something more).  I also agree that each species is unique and would respond
in a unique fashion to extinction pressures.  My point is not that it
couldn't happen but that I do not think that was the critical pressure on
Strombus gigas (and I'm not sure about Turbo marmoratus or any of the
Tridacnids either).  Certainly, the pressures are greater on a long lived
and slow to mature species than on a species that matures in months.  My
country certainly proved you can hunt a large conspicuous animal to the
brink of extinction -- e.g. the American bison.  My point (however fuzzy)
was that there are any number of factors or pressures or whatever you want
to call them that may cause a species to become extinct.  And certainly, we
need to pay attention to all of them.  Which means not getting all worked up
and passing laws against collecting because this is an easy fix (not
necessarily an effective one) while ignoring the hard to do fixes like
development and polution.  I wonder with all of the collecting laws and bans
in California, how the Haliotis population has fared?

Tom Eichhorst in New Mexico, USA (the extinction pressure here is against us
as we use up the water)