Ross,
The April edition of Smithsonian magazine has an article you might be
interested in.  It is titled "We're Scraping Bottom" and describes the
effect of Drag Nets and Dredges  on the seabed biome.  It also mentions that
the December issue of Conservation Biology carries 7 reports on what fishing
does to the ocean bottom.  For those of us who don't subscribe Smithsonians
web site is www. smithsonianmag.si.edu   Look under April 99 at Columns:
Phenomena, Comments and Notes. I don't know if "Conservation Biology" has a
web site.
-----Original Message-----
From: Ross Mayhew <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Monday, March 29, 1999 12:13 PM
Subject: Re: [CONCH-L] collecting (or "harvesting") to extinction
 
 
>        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"!!
>