Date: 5 Feb 1998
From: Vu Do Quynh <vdq66qs@mail.hn.vnn.vn>
To: aqua-l@killick.ifmt.nf.ca
QUESTION:
We are currently working on a project aiming at restocking natural
areas (e.g. mangroves) with hatchery-produced juvenile Scylla serrata
crabs (in the future).
Our work will involve tagging young crabs caught from the wild and
release them in a semi-natural environment (e.g. a large extensive
pond where mangrove trees are planted like it is found in many areas
of the Mekong Delta, Vietnam) to check for the survival rate and
growth through time.
Our first step will be to do a lab experiment where young crabs will
be tagged and kept individually in containers to check for their
survival rate and resistance of the tag (a magnetic internal microtag) to moltings. By the way we are also investigating crab fisheries in the planned experimental semi-natural environment and are looking into the seasonal pattern of young crab population recruitment. For that we have been doing surface plankton sampling every fortnight spring tides (i.e at the period of full moon and no moon) during rising and lowering tidal periods and we are currently investigating the size distribution frequency of crabs caught and sold to local middlemen.
My question is:
Is anybody having data that he would like to share about the growth
size increments (carapace width, or weight) of young Scylla crabs
between a series of incremental molting stages.
Any other comments about our work succinctly presented above will also be appreciated.
Vu Do Quynh
Director Shrimp-Artemia R&D Institute/SARDI
Can Tho University, Can Tho, Vietnam
URL: http://allserv.UGent.be/~booghe/asrdc/
email: vdq66qs@hn.vnn.vn
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COMMENTS 1:
Mud crab resources throughout SE Asia are heavily exploited and over fishing is very common. No country in the region has a management plan and with the heavy fishing on immature and female crabs, we can expect to see a collapse of mud crab fisheries in many countries.
Thus I believe your research is very timely. Are any efforts being
made to work with local fishing communities to develop management
programs to be run by the fisherfolk themselves?
I have been unable to locate a commercial hatchery for Scylla spp
anywhere in the region. Research hatcheries do have some success
from time to time, but survival to the first crab stage is highly
variable and usually very low.
The only country with a management program is Australia. You may
contact Dr. Clive Keenan who works with hatchery and management
programs at Bribie Island in Queensland. His E mail is
keenan@dpi.qld.gov.au. Tagging studies have been done in Australia
so Dr. Keenan may be able to send you some copies of relevant papers. I have only abstracts.
Please let me know if you have any luck with your hatchery work. I
am working with projects in Myanmar, Sri Lanka and Malaysia involving mud crab. However, the future of both the fishery and culture is bleak unless hatchery production can be realized and management programs are put into place.
Charles Angell, clangell@eskimo.com
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COMMENTS 2:
Here are some more precisions and answers to your questions:
We are currently working with the support of a state farm (several
hundreds of ha of mangroves) located at the tip of an island just in
between the two main branches of the Mekong River (Tien and Hau River which passes by Can Tho City). That state farm is doing agriculture (rice production) and aquaculture activities (shrimp and mud crab additional stocking). Next to the farm and the protective mangrove belt there is a large tidal flat where fishermen currently search for mud crabs (juveniles for pond culture, and others for domestic and export market). A major constraint to sustainable fisheries management in Vietnam is the nearly non-existence of
community-based fisheries - Fishing communities (like fisherman
village) do exist but it seems like everyone is on its own. If
regulations can be enforced with large fishing vessels, still fishing
is practiced at several levels, e.g. family hand-picking, fisherman
on foot, rowing boats, sail-boats, light-motored boats to true
fishing boats, etc... Thus a very scattered fishing sector difficult
to control and manage. Most coastal communities in the Mekong
Delta are poor people and fishermen (on foot) are mostly landless
people who have only fishing as income source. We hope that in the
next future, when coming out with serious base data, that then we can
influence decision-makings at the province level as well as the
farm's direction boards.
We are also working on an other project in northern Vietnam (Quang
Ninh province) where efforts for preservation of remaining mangrove
forests and replantation of denuded/abandoned ponds is under way. In
this area we succeeded to reserve the right for exploitation of about
120 ha of mangrove forests for a village community. Main product
of exploitation consist of (Phascolosoma) sipunculid worms and
clams. We are trying to raise consciousness and awareness of those
people that they should try to control their exploitation rate
themselves. There has been quite a consensus against the further
expansion of shrimp ponds which led to the destruction of large
portions of mangrove forests in the early nineties, and thus
deprived the local people from a source of income through the
privatisation of those mangrove areas to the benefit of shrimp
farmers. But there is still a long way to have the people manage
themselves the natural resources that have been put aside for them.
We are just in the phase of collecting data on the rate of
exploitation by controlling data from middlemen in that area.
Vu Do Quynh
quynh_vudo@bigfoot.com