the mangrove areas in the major produc-
ing countries, but data presented in the
figure are from different years: mangrove
areas are represented by figures published
before the exponential growth of shrimp
culture started (Saenger et al. 1983),
whereas shrimp production data are from
1990.
Mangroves are in fact suboptimal sites
for shrimp culture: constructionis diffkult
to mechanize and expensive in the tidal
zone and the soil is very often acidic and
has to be improved at additional cost.
There was only one advantage of selecting
shrimp pond sites within mangrove areas,
namely, the abundance of wild shrimp
seed for trappingfgrowingoperations. Once
shrimp culture became independent of
trapped wild seed, there was no good reason
to place the ponds in mangrove areas; the
more so because, in more productive semi-
intensive systems, tidal water exchange is
not enough and pumping has to be
introduced anyway. Moreover, complete
drainage of the ponds and drying of the
pond bottom is also needed and this cannot
be achieved by gravity alone in the tidal
zone.
Disadvantages of converted mangroves
as shrimp ponds - primarily the
unfavorable experiences gained with acid
sulfate soils - have turned the farmers'
interests further inland. Pond construction
costs on drylands are considerably lower
thanin swamplands and 30 to 40% savings
have been reported from Thailand (FA0
1988). Marginal, salt-affected ricelands,
uneconomic sugarcane fields and aged
coconut plantations have been converted
to shrimp ponds in many countries of the
region (e.g., in Thailand, the Philippines,
Indonesia and Malaysia). While this trend
undoubtedly helped to conserve remaining
mangroves, it involved another
environmental hazard, namely the
salinization of coastal subterranean
freshwater aquifers and hitherto
productive neighboringcroplands (Phillips
et al., this vol.).
Unfortunately, there are no reliable
regional data on the siting of the new
shrimp farms, but a recent survey
implementedin the central part ofThailand
provides some valuable information on
this topic. Chaichavalit (1989) reported
that only 32% of the new farms were
located in converted mangroves (including
nipa palm stands) and as much as 21% of
them occupied former coconut plantations
and other higher grounds. However, almost
half of the new farms were constructed on
the sites of former extensive trapping1
growing ponds or salt farms, which were
once also mangrove areas. The region had
already in 1981 almost 0.5 million ha of
trappinglgrowing ponds (called tambaks
in Indonesia), while the total area of shrimp
ponds in 1990 was estimated at about 0.9
million hectares (Rosenberry 1991).
In the Philippines, some 3l0,OOO ha of
mangroves were deforested since 1920
(Zamora 1989) but the total shrimp pond
area was only about 200,000 ha in 1989
and a significant part of this occupies
former sugarcane and coconut plantations,
coastal ricefields. In Thailand, about
172,000 ha of mangroves were converted
since 1961 (Chantadisai 1989). However,
the total area under shrimp culture in
1989 was only 90,000 ha, a significant part
of which is located outside the tidal zone.
In Indonesia, about 20% of the mangroves
or 800,000 ha are considered to be suitable
for being converted to shrimp ponds
(Adriawan and Jhamtani 19891, but the
total shrimp pond area in 1989 was only
250,000 ha and Indonesia had already
155,000 ha of tambaks in 1980
(Soenodihardjo and Soerianegara 19891,
most of them in use since the 15th century.
Shrimp farmers, after all, are usually
converting mangrove areas already
destroyed by the logging concessions or
pulp-wood, wood-chip or charcoal