The Strombus gigas discussion has brought to the fore several issues
quite relevant to our group, as conchologists (ie, collectors and
amateur natural historians), and as people keenly interested in marine
conservation in general. Most importantly,  the question of how
populations (species can be thought of as assemblages of local
populations which actively or potentially interbereed: extinction of a
species occurs when the last individual of the last local population
dies or is killed) are depleted to low levels which may lead to its
elimination, usually by pushing the population's numbers below a certain
self-sustaining threshhold (as seems to be happening with the right
whale in the Atlantic, certain Panda and Tiger populations, etc etc etc
(we are in danger of losing far more populations than most people
realize, i believe!!)), or in the case of certain very vulnerable
species, the Great Auk and the Passenger Pigeon, by slaughtering  almost
every last individual, leaving the remaining few unable to find a mate.
        As a general principle, populations of marine organisms are far harder
to eliminate than terrestrial populations, when it comes to simply
killing individuals (via collecting, on the small scale, or "harvesting"
for commercial purposes (a euphemism i personally despise!!!!! (but
people look at you like you have 4 heads, if you call it "massacring"!),
on the large scale) without signifigant degradation, disruption or
destruction of habitat - especially true for phyla such as the Mollusca,
which have superb reproductive capabilities.  As long as a population's
habitat remains healthy, it is extremely difficult to kill every last
one, because of the numerous refugia (places to hide) in most marine
environments -  a few individuals can repoproduce rapidly in a suitable
habitat, given little competion!  Also, veligers and other juvenile
forms can be transported in from neighbouring populations, to help
maintain the  genetic diversity needed to collectively survive.  Mollusc
populations in healthy habitats are often capable of sustaining rather
awesome rates of "harvest" - as in the Strombus gigas food industry in
the Carribean, and the completely amazing example of Cypraea moneta in
the Indian Ocean in the sixteenth and seventeenth century ( i read an
account of the amazing tonnage purchased by the Dutch East Indian
Company in their heyday, for use as currency when dealing with many
local Homo sapiens populations in the area, but cannot remember where -
anyone know??). ***HOWEVER***, when habitat is altered so as to
disadvantage a given population,  non-viability can be much more easily
reached, most often through a combination of direct killing in
combination with diminished reproductive success: ie,  "harvesting"
pressures can push populations over the edge far more easily when their
reproductive rate is diminished by habitat damage (the difference
between Fla and the Bahamas, for S. gigas, for example: the latter
populations are under tremendous harvesting pressure, but  are able to
maintain themselves despite this, because their habitats are healthy.
The former are often unable to sustain even mild harvesting pressures,
such as from reckless collecting, for example!).
        The moral is: given healthy habitats, local expatriation (ie,
elimination of a local population), even of heavily-harvested spp, is
nearly impossible for most marine molluscs.  The true villans here are
unsustainable fishing methods (like trawling which destroys producive
habitats such as deep-water corals), reckless and relentless explotaion
of shelf-based resources (sand strip-mining for "beach renourishment" (a
bit like war - lots of "collateral damage" (ie, a lot of innocents are
killed in the process - remember the Gulf War??))), destruction of
wetlands, pollution of all kinds, including agricultural, residential
and industrial wastes (we live in a "consumer" society, remember??),
siltation from deforestation, urbanization and poor agricultural
practices ... need i contine?  So far as marine molluscs go, i would be
so bold as to suggest the conchologists have NEVER been a major
contributing factor in the threatening of ANY local population i have
ever heard of (including even Tridacna gigas, which was indiscriminately
killed for meat and especially for the "size-large" bric-a-brac and
tourist trade).  However, we make exellent scapegoats, being a small,
not-too-vocal visible minority.  Time to change this, and get the facts
into the hands of those who make the laws and regualations.
Didactically Yours,
Ross M.
--
Ross Mayhew:    Schooner Specimen Shells:    Http://www.schnr-specimen-shells.com
"We Specialize in the Unusual"
Phone: (902) 876-2241     Snail Mail; P.O Box 20005, RPO Spryfield,
Halifax, N.S., Canada, B3R 2K9.
But try to find "something for Everyone"!!