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4. Prawn Culture Impacts
4.1 Prawn culture impacts to environment
The environmental problems which may be associated with shrimp
farming are well documented (Macintosh and Phillips 1992; Landesmann 1994;
Pullin et al. 1993; Phillips 1995a and 1995b) and include mangrove deforestation;
reduction of habitat; reductions in shoreline protection; increased coastal erosion;
coastal water pollution; nutrient enrichment; depletion of wild prawn and fish
larvae stocks; land subsidence; salinisation of soils, agricultural land and ground
water, activation of acid sulphate soils; loss of agricultural lands; introduction of
exotic species and the discharge of undesirable chemicals. Whilst these
problems have been identified, quantification of them is difficult.
4.1.1 Deforestation mangrove
The term mangrove refers to salt-tolerant species of tree or shrub which
grow on sheltered shores and in estuaries in the tropics and some sub-tropical
regions. There are about 60 species which occur exclusively in this habitat, and
many non-exclusive species. Mangroves are outstandingly adapted to growing in
seawater, which they desalinate by an ultrafiltration process. Mangrove roots
typically grow in anaerobic sediment and receive oxygen through aerating tissue
which communicates to the air through small pores (lenticels) on the aerial roots
and trunks. Mangroves may occur as narrow fringes on steeper shores and river
banks, or as Mangrove forests in optimum conditions are one of the most
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productive ecosystems; for example a net primary productivity of 23.3
tonnes/ha/year and litter productivity of 10 tonnes/ha/year was measured for a
15-year-old stand ofRhizophora at Matang, Malaysia. The litter (such as fallen
mangrove leaves) is broken down by bacteria, fungi and herbivores, and the
resulting detritus supports food webs including large populations of invertebrates
and fish. The calm waters in the forests are ideal breeding and nursery grounds
for young fish and shrimps, while the aerial roots, lower trunks and mud surface
usually support a varied fauna of oysters, snails, barnacles, crabs and other
invertebrates. The upper part of the mangrove trees is an essentially terrestrial
environment with a fauna of birds, mammals and insects. Mangroves are
affected by the freshwater and nutrient supply which they receive from their
catchment area, and on the other hand have a strong influence on the adjoining
coastal waters and associated ecosystems such as coral reefs, seagrass beds
and tidal marshes. For example, they trap and stabilize sediment which might
otherwise limit the growth of corals.
Most mangrove forests in Malaysia are found along the meandering
coastline of Sabah (350,000 hectares) followed by those in Sarawak (175,000
hectares) and in Peninsular Malaysia (105,000 hectares). Total area of
mangroves in Malaysia is only about 3% (630,000 hectares) of the total land area
of Malaysia. Conversion to shrimp/fish ponds, in addition to settlements,
agriculture, salt beds, overexploitation and other factors, have led to high rates of
mangrove loss ranging from 25% in Malaysia. Most of the shrimp ponds opened
during the 1980's and early 1990's involved the clearcutting of mangroves. Local
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fisherfolk are severely concerned about the increased loss of mangroves as this
has led to decrease in wild stocks and extinction of several commercial fish
species in some places. The Penang Inshore Fishermen Welfare Association
states that its survey revealed that 34 species of fish have become extinct and
another 50 or more are becoming rare in the waters off Penang. Shrimp
aquaculture is considered by many scientific experts to be the largest
contributing factor to present day loss of mangrove ecosystems. The alarming
rate of expansion of shrimp farming along mangrove coastlines throughout the
tropics and subtropics demands immediate attention.
The destruction of coastal mangroves has also brought about coastal
erosion. The coastal villages are susceptible to critical erosion, battered by
strong waves and storms. Their life and property is at stake as the raging sea is
slowly swallowing the coast. Mangrove ecosystems protect shorelines from
erosion, storms, and, as we learned in 2004, from tsunami damage, through their
ability to reduce wave action and wind velocities in coastal areas. Mangrove
ecosystems include the mangrove forest itself; its associated faunal community,
and adjacent and hydrologically linked wetlands. The landward portion of the
ecosystem includes salt flats or salinas, and freshwater streams and wetlands
which ultimately drain to the sea via surface and underground waterways. The
seaward edge of the mangrove ecosystem is the outer edge of the influence of
water flows coming from drainage through mangrove forests and may extend
several miles offshore, affecting associated ecosystems, such as seagrass beds
and coral reefs. International trade is also posing significant threats to mangrove
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forests, another critical coastal ecosystem that is intimately connected to coral
reefs. Mangrove forests serve as important nurseries for many reef species.
They help to maintain coastal water quality by reducing the run-off of sediments,
pollutants and excess nutrients from the land. Nutrients and energy flow between
these habitats as species move between them. Some environmental and
economic benefits of mangroves
Help protect coasts and river banks from erosion
Help protect coastal dwellers from storms and storm surges
Help reduce peaks of nutrient and sediment discharges from coastal rivers
Help trap sediment and build new land
Help reduce atmospheric CO2 levels by fixing and storing carbon
Produce leaf litter and other detritus that support coastal food chains
Provide nursery and feeding ground for fauna, including commercially
valuable fish, shrimp, crab, gastropods and bivalve species
Provide timber and fuel wood for coastal dwellers
Provide other products like honey and medicinal drugs
Enhance biodiversity
Provide aesthetic and recreational values
Provide scientific, educational and cultural values
Mangroves are not the best site for shrimp culture, as they have
potentially acidic soil. Shrimp ponds may have problems with low pH, which is
bad for the health and survival of shrimp. Also, when mangroves are converted
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into aquaculture ponds, valuable environmental benefits are lost. In general, it is
better to set up aquaculture ponds on higher land behind mangroves. The putting
up of new aquaculture ponds within mangrove areas should be discouraged.
However, brackish water shrimp ponds have already been built in many areas
due to the mangrove located near the sea shore to accommodate prawn culturist
with sea water stock used in prawn and shrimp culture.
Figure 9: Mangrove area in Malaysia.
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Table 5: Total landing of various fisheries products on the west and east
coasts of peninsular Malaysia.
4.1.2 Impacts of Ponds Discharge to Soils and Ecology
Role of nutrients and organic matter Studies with- intensive shrimp
farming suggest that nutrients and organic matter in shrimp pond wastes have
potential for the following impacts:
Reduce dissolved oxygen in receiving waters, due to discharge of waste
water low In dissolved oxygen and breakdown of dissolved- solved and
participate organic matter and other waste materials (BOD and COD);
Hyper-nutrification and eutrophication of receiving waters, resulting in
increased primary productivity (with potential risks of phytoplankton
blooms).
Alteration of biological community structure and secondary productivity
Increased sedimentation due to organic matter leading to changes in
productivity and benthic community structure, plus possible situation.
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Such impacts depend on the quantum of waste water outflow and the
capacity of the environment to assimilate the waste materials. It is, therefore,
desirable to match loads with the capacity of the environment to accept the waste
materials.
Prevention Steps to Avoid Impacts of Ponds Discharges
Problems encountered during aquaculture experiments in ponds
constructed on acid sulfate mangrove soils are described. Entry into the ponds of
acid water with a high iron content and activity of iron oxidizing bacteria were
identified as major contributors to the problems. Design features and
management practices which minimize entry of acid water and reduce the
harmful effects of acidity and iron are presented. These include reducing the size
of the dikes, using a pumped water supply and employing mechanical circulation
and mixing of pond water.
Efforts to develop pond culture at the Brackish water Aquaculture
Research Centre, Gelang Patah, Johor Bahru, Malaysia have encountered
problems. Mortality of the species cultured is high and growth is frequently slow
due to a number of complex conditions associated with acid sulphate soils. The
major problem is entry of acidic water containing high levels of dissolved iron into
the ponds. There are three principal ways by which the acidic water enters a
pond. The most important is runoff of rainwater which becomes acidic after
reacting with oxidized pyrite in the soil (Potter, 1976). Another problem is entry of
acidic dike pore water during draining and filling the ponds with tidal water. There
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is also some addition by seepage through the dikes. The pond bottom is not a
continuing source of acid once it is leached well and kept submerged.
Use of chemicals
Chemicals should be avoided in shrimp culture ponds for prevention or
treatment of disease, as feed additives, disinfectants for removal of other fish or
for treatment of soil or water. However, chemicals may be required in hatcheries.
Entry of such chemicals into the natural waters from the hatcheries should be
carefully monitored and steps should be taken to remove such materials from the
waste waters.
Use of fertilizers
Both organic and inorganic fertilizers are used widely in semi-intensive
culture systems for promoting the growth of fish food organisms. particularly for
the early postlarval stages. This may contribute to the nutrient load in receiving
water. Therefore, as far as possible only organic manure/fertilizers and other
plant products should be used for such purposes
Use of piscicides
Similarly, piscicides and mollusclcides are widely used for removing
predators and competitors from shrimp ponds. It would be advisable for
aquaculturists to use only the biodegradable organic plant extracts for this
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purpose as they are less harmful than the chemical agents. Use of chemical
piselcides in culture systems should be avoided.
Use of chemotherapeutants
Some of the chemotherapeutants such as formalin and malachite green
which are commonly- use as disinfectants are known to be toxic and many affect
adversely the pond ecosystem. The external waters, etc. and hence their usage
in culture system should be avoided.
Use of antibiotics/drugs
A number of antibiotics used in shrimp culture for preventing outbreak of
disease are harmful and may result in development of shrimp pathogens
resistant to such drugs and the transfer of this pathogen's into human beings
might result in development of resistance in human pathogens. The use of
antibiotics/drugs in culture system, therefore, should be avoided.
Outbreak of disease in shrimp culture system is related to the
environmental factors such as deterioration of water quality, sedimentation and
self-pollution. The production losses are also linked to the acid sulphate soil
particularly in the areas. Another consequence of industrial shrimp farming is the
use of antibiotics, pesticides, fungicides, parasiticides, and algicides. To guard
against diseases farmers also use a large amount of antibiotics during production
as well as toxic chemicals between harvests to sterilize the ponds. The result is
that human consumers of tropical shrimps produced in this way are eating food
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containing high levels of antibiotics. Many of the substances used in this activity
are prohibited in some countries due to their carcinogenic effects. Regarding
antibiotics, some of the ones that are used in shrimp farming are the ones used
in humans, which might decrease the effectiveness of antibiotics against
diseases. In Malaysia, there are regulations limiting the amount of chemicals
used.
Use of soil with least acidity
The intensity of acidification in any area is patchy and in general the
deeper the soil is excavated the more acid the soil. Also, the content of iron,
sulphur and aluminium increases with depth. Frequently, the top 2030 cm of soil
is good. An example of this can be seen in a study of soil distribution in the delta
of the Sarawak River (Andriesse et al., 1972). In the Sarawak River Delta there is
only a small area of Pendam series soil which has acid and potentially acid
sulphate soil (pH 3.9) in the surface 15 cm. Most of the area is composed of
Rajang series soil which is characterized by top soil with a near to neutral pH and
subsoil (6075 cm depth) which is potentially acidic. If brackish water ponds were
built in the Pendam series area they would experience problems no matter how
they were constructed. In the Rajang series area severe problems would be
encountered if it was decided to excavate to expose the potentially acid sulphate
soil which occurs at depth. It is preferable for ponds to be constructed with only
minimal excavation. The land should be levelled and only enough of the neutral
top soil to build the dikes should be used.
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At this point it should be remembered that pH is a logarithmic function.
That is, pH 4 is ten times more acidic than pH 5, and pH 3 is ten times more
acidic than pH 4 and 100 times more acidic than pH 5. Thus tremendous
leverage is obtained when soil with a higher pH is used for the dikes. It may not
be necessary to have the dike soils near to neutrality to obtain significant benefit.
As pointed out in this report many of the problems in shrimp culture involve iron.
Iron is not soluble at pH 4 and above. There are few places where the surface
layer is lower than pH 4.
The dikes should be small as possible
In most places it is necessary to excavate in order to locate pond bottoms
at a level where tidal fluctuation can be used to fill the ponds with water. That
was the case at the Gelang Patah Research Centre. Natural ground elevation at
the site rose to 1.8 m above mean sea level (MSL). Excavation was undertaken
to situate the pond bottoms at 30 and 45 cm above MSL. As the excavated soil
must be disposed of, in this case it was incorporated into dikes which resulted as
massive. The dikes around one 0.25 ha pond adjacent to the main dike were
measured as an example. The height of the dikes varied from 1.1 to 2.8 m above
the water line. Distance from the mid-point of the dike to the water varied from
4.5 to 16 m. The surface area of the dike amounted to about 36 percent of the
total area and 55 percent of the pond water surface. The great soil surface area
ensures that a large amount of runoff will enter the pond when it rains, and the
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fact that it was excavated from depth ensures that the runoff will be very acidic,
with pH under 3.5.
If the pond had been built by levelling the land and using only top soil to
construct a small dike it is assumed that the height of the dike would be 0.5 m
above water and the average distance from the mid-point of the dike to the water
would be only 2.2 m. This would reduce the surface area of the dikes to only 18
percent of the total area and 15 percent of the water area. Rainwater runoff
would be drastically reduced, as in addition to the reduction in the surface area of
the dike, the volume of water in the pond had been increased. In the existing
pond a 10 cm rain would result in 137 m3 of rainwater runoff into 2 400 m3 of
pond water. In a non-excavated pond only 60.5 m3 of rainwater would run off into
3 312 m3 of pond water. The amount of run-off would be reduced from 5.5 to 1.8
percent of the volume of water in the pond. Even if the runoff was acidic the
effect on the pond would be drastically reduced, but as seen earlier the top soil
would probably be less acidic.
An experiment was carried out to assess the effect of adding acid water to
the ponds. Thoroughly dried dike soil was pulverized and different amounts were
added to two beakers of tap water to make them acidic. One solution was made
with a pH of 3.44 and another with pH 2.88. Each of these solutions was added
sequentially to brackish water from the ponds which had a pH of 6.9. The
resulting pH values were then plotted as a percentage of total water volume. This
showed that adding 5.5% of pH 2.88 water reduces the pH of the pond water
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19.5% and adding the same amount of pH 3.44 solution reduces pH by 9%.
Adding only 1.8% of the pond volume at the same pH would reduce the pond
water pH by 8.8 and 5.2% respectively. Thus by reducing the amount of runoff
from 5.5 to 1.8 percent of the pond volume the reduction of pond water pH would
decrease from 19.5 to 8.8%.
This also points to the importance of reducing pH of the runoff water. A
reduction of only 0.56 pH units would exert about the same effect as reducing the
amount of runoff by 67 percent. The change in pH would be reduced from 19.5 to
9 percent.
Increasing the water volume in a pond
The volume of water in a pond relative to the surface area of dike subject
to runoff can be increased in two ways; increasing depth and increasing pond
size. Both of these options have serious limitations if a tidal water supply is
planned. The primary problem revolves around the elevation of the pond bottom.
In order to ensure an adequate supply of tidal water the land must be excavated
to construct the pond bottom at the proper elevation in relation to the tide. This
usually requires some compromise. If the bottom is situated low enough to
maintain a high level of water in the pond it is usually not possible to exchange
water on neap tides. If water can be exchanged only on spring tides,
management is restricted. If the bottom is too low, it is not possible to drain the
ponds for harvesting and certain pond preparation procedures. Also, as already
pointed out, excavation into the deeper zones exposes soils with a lower pH, and
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the soil removed must be incorporated into dikes or removed. Removal is very
expensive. If the land has to be excavated, the cost of building very large ponds
becomes prohibitive because the earth from the centre of the pond must be
moved a long distance. In most locations ponds larger than 1 ha probably would
not be economic if they have to be excavated.
Eliminating fluctuations in water level
It would seem that if water in the pond is of poor quality it should be
changed. This has some bad effects. Draining and refilling a pond during water
exchange causes movement of water in and out of the dike. The pH of interstitial
dike water can be as low as 3 and iron content ranges from 100 to 200 ppm. Iron
content of rainwater runoff is only of the order of 2025 ppm. So even if less
water is involved in the exchange of pore water its higher iron content increases
its relative importance (see Chapter 2 of this report). This is an important factor
even during dry periods and may account for a great deal of the iron-related
problems. The only way to prevent this is to maintain a constant level of water in
the pond.
Increasing pH and decreasing iron of run-in water
Several methods have been suggested for reducing the amount of acid
and iron entering the pond. One of the most important is to establish vegetation
on the dike and at the water's edge. Vegetation on a dike stabilizes the surface
and prevents erosion so that the soil has time to weather before it is washed
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away. On acid sulphate dikes with high clay content the surface cracks with only
a small amount of drying. During the next rain many of the small dry particles are
washed into the pond. As the soil particles are fully oxidized they contribute a
maximum amount of acidity and iron to the pond water. Perhaps an equally
important factor is that the fairly large pieces of soil form a porous zone right at
the water's edge. This acts as a sink for small floating organic particles which are
washed up to the shore by wind. Often the organic material which originates on
the pond bottom (benthic bluegreen algae) is coated with iron. Also films of
oxidized iron which form on the pond surface are blown on the pond edge by
wind. Consequently, high levels of iron and organic matter accumulate in the soft
intertidal zone. Due to the high level of organic matter the soil becomes
anaerobic and in the absence of oxygen the iron assumes the soluble Fe++ state.
During drawdown for tidal water exchange the pore water high in iron seeps back
into the pond and the cycle starts again. Planting grasses such as buffalo grass
(Paspalum conjugatum) and digit grass (Digitaria decumbens) prevents this,
because the grasses trap the soil particles before they enter the water.
Furthermore, these grasses take up iron from the soil thus removing them from
the cycle (Cook et al., 1984).
The main point brought out in the preceding sections is that in areas with
acid sulphate, or potentially acid sulphate soil, ponds should be built with a
minimum of excavation. Such ponds would naturally have a high bottom
elevation and it is unlikely that tidal water exchange would be effective. Water
would have to be pumped into such ponds. Pumps are frequently used to fill
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ponds in Thailand and South America, but many people still question the use of
pumps as an economically viable alternative to free tidal water.
A case study was made by Gedney et al., (1983) to compare cost factors
involved between constructing and operating tidal water exchange aquaculture
farm systems and a pumped water system. A comparative assessment was
made of three different systems:
A tidal farm excavated to a depth of +0.3 m above mean sea level
(MSL) from a natural ground elevation which varied from +0.9 m to
+1.2 m.
A tidal pond system excavated to a depth of +0.3 m above MSL
from natural ground elevation which varied from +1.5 to 1.8 m.
A pumped water pond system at a natural ground elevation varying
from +1.8 to +2.7 m above MSL.
The study showed that a pump system offers advantages in terms of lower
costs. A summary of construction and operating costs for the different pond
system is given in Table 1. As the study was done at the Brackish Water
Aquaculture Research Centre, costs and benefits reflect Malaysian conditions.
Acidity of the pond bottom soil is not really a problem. After a short period
of flushing and submergence the top layer becomes neutralized by carbonate in
seawater and deeper layers become anaerobic. In either case the pH rises. As
pointed out earlier iron is harmful. It accumulates in the pond, and once in the
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pond it acts independently of acidity. It recycles between a reduced state in the
pond sediments and an oxidized state depending on bacterial action and the
quantity of oxygen in the soil. Bacteria oxidize the iron and the bottom flora
becomes coated with oxidized iron. During the day the benthic algae, coated with
oxidized iron, float to the surface where wind action carries them to the side of
the pond. This material accumulates at the pond edge and becomes incorporated
in the loose unconsolidated sediments carried into the pond from the dike by
rainwater. Gradually as one layer forms on top of another the bottom layers
become anaerobic and the iron reverts to the soluble ionic state. Then it is
leached back into the pond in dike pore water during drawdown for tidal
exchange.
It is advisable to remove as much iron as possible from the pond. Addition
of lime would just bind more iron. One way to remove the iron is to make the iron
change to a soluble form and then flush it from the pond. The iron is soluble
below pH 4. A good way to remove iron would be to fill the pond with acid to
dissolve the iron. This can be accomplished by drying the pond thoroughly and
tilling it to aerate and dry the soil at deeper levels.
After the soil is completely dry, just enough water is let in to cover the
bottom. This water will become very acidic and the iron will be dissolved. The
water is then drained from the pond and the flushing process repeated until the
water pH rises above 4. If too much water is let in during the initial filling, pH will
rise above 4 and most of the iron will precipitate back out of solution.
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Furthermore, moist soil should not be flushed. The pond bottom must be
thoroughly dried to oxidize the iron. After the pH of the water no longer drops
below 4, flushing should be continued with the water level as high as conditions
permit. The entire system inside the perimeter dike should be flooded if possible.
This will leach acidity from the dikes.
Planting grass, especially at the water edge is recommended. Grass at the
water's edge prevents entry of small oxidized soil particles which are washed into
the pond by rainwater and contribute iron to the pond. Prevention of the
accumulation of these loose soil particles at the water's edge reduces the amount
of soil pore water which enters the pond during drawdown. The plants also take
iron up from the soil, and its removal from the recycling process is beneficial. It
must be mentioned that maintaining water level at a constant depth would help
reduce the recycling of iron.
4.2 Prawn Culture Impacts to Social
Although prawn farming is still a small industry in Malaysia, the social
impacts have already become evident. The mangrove ecosystems provide direct
food resources and habitat for many forms of fish and wildlife, including many
directly harvested by subsistence-based villagers and fisherfolk living in or
adjacent to the mangrove ecosystem, and commercial harvests of fishery
resources, including wild-caught shrimp, crabs and fish. Among the most
worrying are the loss of livelihood and income of small coastal fisherfolk due to
mangrove loss and fish decline, negative changes in agricultural practices, and
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human rights violations. The most controversial shrimp project in Malaysia is in
Kerpan (Kedah). Samak Aquaculture was approved as a joint venture company
in 1993 where villagers where ordered by government to sell their paddy field to
be converted to shrimp ponds.
Therefore, access to the sea front and other common resources to the
coastal communities by the aquaculture units should be ensured. The interests of
the communities and organisations in the area should be safeguarded.
Large-scale shrimp aquaculture may bring an excessive demand on land
resources, resulting in multi-user conflicts. Construction of shrimp ponds may
make inroads into agricultural land. States must undertake surveys to identify
lands which are fit for different purposes. They should discourage conversion of
agriculture land for aquaculture. Construction of shrimp ponds on marginal land
not fit for cultivation alone should he permitted.
4.3 Prawn Culture Impacts to Economy due to Viral Diseases
Prawn culture had been an alternative economy source and income
generation of villagers in Malaysia. In the past years, the aquaculturists mostly
are villagers with lack of knowledge in prawn culture relating to the lack of
scientific research spread out to the aquaculturists. During this time, million of
ringgit loss due to the outbreak of disease in shrimp culture system which is
related to the environmental factors such as deterioration of water quality,
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sedimentation and self-pollution. The production losses are also linked to the
acid sulphate soil particularly in the areas. However, in recent years, the
production of cultured shrimp has markedly decreased as a result of serious viral
disease outbreaks. Especially, the increased severity of widespread White Spot
Syndrome Virus (WSSV) infection is the most serious threat to stable
aquacultural production. In the case of Malaysia, outbreak of this disease was
almost the same as Thailand situation that was WSSV disease occurring as
serious problem from 1996. A lot of farms have given up shrimp culture due to
heavy loss incurred by WSSV until 1997. Field research was performed through
1998 and 1999 on the occurrences of WSSV at farms in Malaysia. Dark-field
microscope observation and Japanese PCR methods for PRDV detection were
used for this research, because both methods were confirmed to use for
detection of Malaysian strain of WSSV.
From this research, WSSV outbreaks were found in Penang, Kedah and
Sarawak State, and information of the occurrence of viral disease was obtained.
Almost all prawns in the ponds were dead by this disease. These dead prawns
were showing many clear White spots on their carapace. Pathogenic viruses
were confirmed by PCR from the samples WSSV. In this etiological study, as for
the infection routes, it could be supposed two ways. One was that the prawn fry
had been infected with this virus, and another was from supplied seawater
containing the virus particles. As one of the preventive countermeasures against
viral diseases, inactivation methods for WSSV were studied. This viral
inactivation was tested with formalin and halogenous disinfectants and sodium
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hypochlorite. These chemicals were mixed with the virus and injected to the
healthy prawns. As a result of these experiments, no mortality was shown using
0.25% effective chlorides in sodium hypochlorite and 0.5 ppm formalin. From
these results, sodium hypochlorite of halogenouse disinfectants showed the
effective inactivation even under lower concentration. It was suggested that these
disinfectants were extremely useful for the WSSV inactivation.
Figure 10: Prawn with White Spot Syndrome Virus (WSSV)
5. Prawn Culture Site Selection and Legislation
5.1 Site selection and culture management
A vast majority of problems affecting the shrimp culturists as well as the
environment could be avoided by better site selection and improved culture
management. Site selection process should include proper environmental impact
assessment. The existing criteria for site selection also need to be reviewed and
consideration should be given to long-term capacity of the area to sustain
aquaculture development.
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5.2 Master plan for development
Detailed master plans need for development of prawn culture through
macro and micro-level surveys of the potential areas and conation of coastal
area delineating the land suitable and unsuitable for aquaculture using the
Remote Sensing data, ground truth verification, Geographical Information
System. (GIS) and socioeconomic aspects should be considered.
5.3 Environment Monitoring and Management Plans (EMMPS)
The shrimp culture units with a net water area of 40 hectares or more shall
incorporate an Environment Monitoring Plan and Environment Management plan
covering the areas mentioned below:
Impact on the water sources in the vicinity
Impact on the waste water treatment.
Impact on drinking water sources.
Impact on agricultural activity
Impact on soil and soil salinisation
Green belt development (as per specifications of the State Pollution
Control Board)
All farms of 10 hectares and more but less than 40 hectares shall
furnish detailed information on the aforesaid aspects.
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5.4 Environment Impact Assessment
An Environmental Impact Assessment (EIA) should be made even at the
planning stage by all the aquaculture units above 40 hectares size. For 10
hectares and above a statement will be required to be given in the detailed plans.
The State Pollution Control Boards should ensure that such a EIA has been
carried out by the aquaculture units seeking No Objection Certificate from them,
before giving clearances for such projects.
5.5 Feed quality and its management
The quality of feed plays an important role in waste output in shrimp
culture, and there is scope to Improve pond environment by good feed
management. Nutrients and organic loads are higher in ponds where shrimps are
fed within trash fish and fresh diets than where palletized moist or dry feeds are
used. Fresh diets, infrequent feeding and high stocking densities increase
nitrogen loads in the waste water from the shrimp farms. A considerable amount
of detritus and wastes often accumulated- on the pond bottom, in areas where
water circulation is slow, leading to increased BOD and release of harmful gases,
which could cause stress on bottom living shrimps. On the contrary, regular
feeding with pelletised diets is known to maximize the growth of shrimps and
minimize the nutrient enrichment of the waste water.
The feed waste plays an important role in the total waste loadings In the
environment. This is because; feed settles directly on the pond bottom and the
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feed wastage can have a significant effect on sediment quality and ultimately the
health of the shrimp which normally live at the bottom.
Hence the use of wet diets such as fresh fish and invertebrates has to be
reduced and preferably avoided in shrimp aquaculture systems. Feed
Conversion Ratio (FCR) should also be optimised. Monitoring of feed input is
required to keep feed wastage to the minimum. Similarly, careful monitoring of
standing stock in the ponds will also help to ensure that correct feeding levels are
observed.
5.6 Rules and regulations governing Aquaculture
The law governing fisheries in Malaysia is contained in the Fisheries Act
1985. Under this Act, the Fisheries (Marine Culture System) Regulations 1990
have been made and gazetted in 1990. Culture systems covered under these
Regulations include rack and pole culture, raft culture, cage and pen culture, and
on-bottom culture systems.
Besides these Regulations, the Government has also introduced various
incentives for the development of aquaculture in the country (Hoo, 1985). These
incentives include pioneer status, investment tax credit and export incentives.
5.7 Shrimp aquaculture in international environmental treaties
The ecological and social impacts of shrimp aquaculture have been
brought to the attention of two international environmental treaties that have been
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developing policies and programs for the sustainable management of coastal and
other ecosystems. These are the RAMSAR Convention on Wetlands and the
Convention on Biological Diversity (CBD).
The Forest Peoples Programme, an ISA Net (Industrial Shrimp Action
Network) member organisation, made an intervention highlighting the impacts of
shrimp farming on coastal and marine ecosystem and local communities at the
Conference of the Parties 4 (COP4) of the CBD in May 1998 in Slovakia.
The following year several ISA Net members participated in the 7th
Conference of the Parties of RAMSAR and at a workshop on Indigenous Peoples
and Local Communities' Participation in Wetland Management during the 13th
meeting of the Global Biodiversity Forum (GBF) which preceded the RAMSAR
meeting (San Jos, Costa Rica, 7-18 May, 1999). The presentations made by
four representatives of local communities were well received at the GBF and ISA
Net's recommendations were discussed at the RAMSAR Conference. As a result,
a paragraph was added to one of the final resolutions (Resolution VII.21,
Enhancing the conservation and wise use of intertidal wetlands), calling for the
suspension of the promotion, creation of new facilities, and expansion of
unsustainable aquaculture activities harmful to coastal wetlands until measures
aimed at establishing a sustainable system of aquaculture that is in harmony with
the environment and local communities are identified.
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ISA Net members also participated in discussions and amendments of the
Guidelines for establishing and strengthening local communities' and indigenous
peoples' participation in the management of wetlands, which were eventually
adopted as Resolution VII.21 and VII.8 of the COP.
Getting useful language into international conventions, however, can only
be considered an achievement if they become effective tools to be used by local
organisations in their efforts to protect their environment and livelihoods. NGOs
and CBOs in Ecuador and Honduras have so far tried to use the paragraph on
aquaculture of RAMSAR Resolution VII.21 in order to stop further expansion of
shrimp farming in ecologically sensitive coastal ecosystems. So far, it seems that
the RAMSAR language might have been helpful in supporting the effort of
Ecuadorian NGOs trying to stop the introduction of new policies that would have
included the privatization of parts of the coastline for the benefit of shrimp
farmers. On the other hand, it does not seem to have been particularly useful in
the Gulf of Fonseca, Honduras, despite the fact that part of the Gulf is a
RAMSAR site. Effective follow-up needs to be organised to make sure that
language developed in RAMSAR does not remain empty words.
Meanwhile, a programme under the CBD, namely the Jakarta Mandate on
Coastal and Marine Biodiversity, has developed a 3-year work plan for the
conservation and sustainable use of marine and coastal biological diversity. This
includes a section (programme element 4) on mariculture, whose main
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operational objective is to assess the consequences of mariculture for marine
and coastal biological diversity and promote techniques that minimise adverse
impact.
5.8 List of Relevant Institutions
Training of aquaculture extension workers within the Department of
Fisheries Malaysia is conducted from time to time by the Fisheries Research
Institute (of the Department of Fisheries, Ministry of Agriculture Malaysia) at its
headquarters in Penang, and also at its branches, i.e. at the National Prawn Fry
Production & Research Centre, Kampung Pulau Sayak, Kedah particularly in all
fields of coastal aquaculture; at the Brackish water Aquaculture Research
Centre, Gelang Patah, Johore in certain aspects of brackish water pond
management; and at the Freshwater Fish Research Centre, Batu Berendam,
Malacca in special courses on freshwater fish breeding and culture. The training
courses are organized by the Extension and Training Division of the Department
of Fisheries Malaysia, and the courses are usually conducted jointly by staff from
this Division as well as from the Fisheries Research Institute and its branches.
Certain courses for aquaculture extension workers are also organized and
conducted by the Extension and Training Division at the Fisheries Training
Institute, Batu Maung, Penang.
Many of these endeavours have proven non-sustainable with the result
that large areas of ponds have been left idle and disused, some have been
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abandoned and new sites are being developed in an effort to maintain
production. This presents a major challenge for both coastal resource managers
and pond owners who will have to address the question of what to do with
disused ponds. There are three basic options. The first is to rehabilitate the pond
sites so that they can be put back into shrimp production. The second is to
rehabilitate the pond sites so that they can be put to some alternative,
sustainable use such as salt production. The third option is to restore the
environmental conditions within the pond site and the surrounding area, and to
re-establish a productive mangrove ecosystem. Each of these options is heavily
influenced by the causes of failure of the pond operations and the conditions
which remain in the pond after disuse. This paper briefly explores the issues that
must be faced if rehabilitation and restoration are to be successful.
Figure 11: Suggested sequence for improving the separate farming
system
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Figure 12: LKIM aquaculture programs in Peninsular Malaysia
6. Recommendations to Prawn culturist
6.1 Small-scale improved extensive and semi-intensive shrimp
culture
Increasing the stocking density (up to, but not more than, 10 per meter)
and the survival rate ofP. monodon in the pond can improve the contribution of
shrimp farming to the livelihood of small-scale farmers in coastal areas. This can
be achieved through modest intensification, together with better pond design,
good quality seed and improved farm management practices. A range of options
for improvement require different levels of investment. It is necessary to show
farmers a sequence of steps they could take to increase their income. These
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steps depend on the condition of the farm, individual financial circumstances and
experience.
The three main requirements
1. A good pond
2. Strong, high quality and disease-free seed
3. Good nursery care during the first 20-25 days of stocking
Some general suggestions on farm layout
Remember that coastal mangrove systems are highly dynamic and their
characteristics often change. What is seen now may not be the same in 10-20
years time. Try to anticipate future changes and make plans with these in mind.
This will help avoid future problems that might be costly to fix.
Try to keep a 20-30 m wide belt of mangroves along the waterfront to
reduce erosion and provide a nursery for wild aquatic species.
Try to maximize the benefit of mangroves by arranging the location to
allow incoming or outgoing water to pass through the trees.
Pond design
A small pond with a water area of about 2000 or 2500 sq m is better than
a much larger pond. Big ponds are more difficult to manage. Start with one pond,
and then add another as capital becomes available. This will help reduce the risk
of losing shrimp through disease. No more than three ponds of this design should
be built. See suggested sequence for the two main farming systems in the
illustrations.
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Some useful tips on pond preparation
Use a sedimentation pond to improve water quality if the intake water
has low transparency, is polluted or otherwise of low quality. Generally the water
surface area of the sedimentation pond should be at least equal to the water
surface area of grow out ponds. The sedimentation pond can be stocked with P.
monodon at a density of 1-3 per sq m or it can be used for wild shrimp culture.
Cannot dump the excavated material into the river or in mangrove
areas. Use it to build an area above the tidal limit, which can be used for
terrestrial crops or livestock production. Diversification can help reduce the risk to
the household and provide a more stable income.
Make sure the average pond water depth is 1 m.
Use a cement water gate that is at least 1 m wide. If necessary, use
plastic sheets or fibro-cement roofing material to prevent water leakage through
crab burrows along the sides of the water gate (refer to the diagram on the right).
Outer levees (or dikes) should be at least 4-6 m wide to reduce leakage
(10 m is preferable). The levee (dike) around the pond should be at least
0.5 m higher than the highest tide to reduce the risk of shrimp being washed out
of the pond by unusually high tides or storm surges.
After constructing or after cleaning the pond, open the watergate and
allow the tide to free flush the pond for at least a week. Put a net at the water
gate to prevent entry of predators (e.g., fish). Avoid using chemicals to kill
predators. If absolutely necessary, use only sparingly. Use Derris root or tea
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seed powder, both natural products, if pesticides are needed. In some areas with
acidic soils, it may be necessary to apply lime.
Prepare a nursery area at least 1 week prior to stocking, using fine net
(equal or less than 1mm mesh size) to cordon off the nursery from the rest of the
pond. The size of the nursery area should be calculated for a stocking density of
about 35-50 per sq m.
Viral and bacterial diseases are more difficult to manage. Using disease-
free seed is the first step that farmers can take to reduce the risk of diseases.
However, viral and bacterial pathogens are probably present in most wild shrimp
populations, so that there is always a risk that disease can be transferred from
wild to cultured shrimps that were initially healthy. Crabs can also be vectors of
some shrimp diseases. Hence, it would be best to exclude wild shrimp and crabs
from the grow-out pond. Shrimps, like all animals including humans, are more
likely to contract a disease if they are weak or stressed. Good pond and water
quality management practices that keep shrimps strong and healthy will also help
reduce the risk of death from viral and bacterial disease.
The Penang Inshore Fishermen Welfare Association (PIFWA) has recently
held a workshop on the importance of mangroves. Fisherfolk were aimed to
highlight what they suppose to know about prawn culture and mangrove forest
which is an inherent part of their livelihood since it is closely related to fish catch.
Without mangroves there will be no fish in the sea since mangrove play a vital
role as intermediaries between marine and terrestrial ecosystems.
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Figure 13: Suitable Location of Prawn ponds.
Figure 14: Agriculture land is unsuitable location for prawn ponds.
Figure 15: Site Selection of prawn ponds near the sea water source.
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7. Disuse and Abandonment of Prawn Farm Ponds
7.1 Causes of Disuse and Abandonment of Shrimp Ponds
Disease has been widely cited as a cause of production failure, and the
shrimp industry has seen the development of a variety of diseases which have
spread from one shrimp culturing nation to another. Aside from disease, the
development of acid sulphate soils has been cited as either a direct or indirect
cause of production failure These soils exist as 'potential acid sulphate soils'
(P.A.S.S.) in many mangrove areas, and as a result of the excavation and
construction of shrimp ponds P.A.S.S. may become actual acid sulphate soils
(A.A.S.S.). Upon wetting, these soils release large quantities of acid into pond
water and also toxic levels of iron and aluminium. Research in South East Asia
reveals that acid, iron and aluminium are directly responsible for fish and prawn
losses and general low productivity, (Simpson and Pedini 1985). Acid conditions
(and poor water quality in general) may indirectly cause production failure by
increasing physiological stresses, and decreasing the immune system response.
7.2 Environmental Condition of Abandon Shrimp Pond
The environmental conditions remaining after abandonment may be more
important than the causes of failure, and may be unrelated to the cause(s) of
failure. For instance in Malaysia, many ponds are said to be disused as a result
of white spot disease. However, the major obstacle to the redevelopment of
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these ponds is not the prevalence of disease, but the remediation of acid
sulphate soils which may persist for many years after abandonment.
The ecological effects of acid sulphate soils have only recently begun to
be clearly identified. The acidic water which results from acid sulphate soils
destroys food resources, displaces biota, releases toxic levels of aluminium,
precipitates iron which smothers vegetation and microhabitat and alters the
physical and chemical properties of the water. Persistent alterations to pH have
been shown to lead to changes in the flora and fauna in an area, by favouring
acid tolerant plants and animals. This could have implications for attempts to
restore the mangrove ecosystem and its resident flora and fauna. Insufficient
research has been carried out to assess the number of shrimp ponds.
In addition to the activation of acid sulphate soils a further consideration,
unrelated to the causes of failure, are the alterations to soils which are likely to
occur as a result of the clearance of mangrove, shrimp cultivation and
abandonment. Ignoring the changes from shrimp culture which are likely to vary
with farming method and culture intensity, the effects of clearance and
abandonment may include accelerated soil erosion due to increased surface run
off and subsurface flow; decrease in soil water storage capacity; reduction in
biodiversity of soil fauna; transport of sediments, dissolved inorganic and organic
constituents and principal nutrients; and depletion of soil organic matter through
leaching and mineralisation.
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The abandoning of aquaculture developments represents a significant
challenge to the productive use of coastal areas in the future because of the
limited land use prospects for vast areas of former rice fields and mangrove
forest. The rehabilitation of these areas is complicated by the fact that many of
the environmental conditions that once fostered the growth of mangrove forests
have been removed or severely altered. When considering options for
redeveloping disused ponds, it is important that the environmental parameters
remaining in a pond are identified. To date little work has been conducted to
elucidate the conditions found in disused ponds, or to identify what implications
these may have for future uses. Disused ponds are likely to be unstable and
actively deteriorating and may represent a risk to neighbouring habitats, and
unless managed may become progressively more difficult to rehabilitate or
restore. Means of assessing such risks should be developed.
7.3 Restoration of mangrove areas
There are now strong signs of an emerging mangrove-friendly mariculture
industry. This initiative, presently experimental and confined to Association of
Southeast Asian Nations (ASEAN) countries, involves the combination of
reforestation with culture of fish, crabs or shrimp. It is an attempt to develop and
disseminate responsible culture technologies. Mangroves are also being
promoted as environments for culture of mud crabs in pens, a technique that
eliminates the conversion of coastal areas to ponds. In the Philippines, crab
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farming in tidal ponds is already an established industry and crab farming in
mangrove areas shows great potential.
According to Global Aquaculture Association (GAA), the exploitation of
mangrove areas for new shrimp farms has essentially stopped and many areas
are being reforested. Studies using satellite photos indicate that mangrove forest
areas actually have begun to increase in shrimp farming regions in Honduras and
Ecuador.. In a review of effects on mangroves, the GAA also claims that shrimp
farming has accounted for less than 5% of the mangrove loss, and further losses
due to shrimp farming have virtually stopped, due to regulatory and educational
efforts.
The 2003 synthesis report by the World Bank, NACA, FAO, WWF
Consortium report on Shrimp Farming and the Environment contains a section on
mitigation and restoration. Rehabilitation of mangrove areas that have been
cleared for shrimp farming has been undertaken in some areas. This is neither
difficult nor costly as long as an appropriate hydrologic regime can be re-created.
This is not easy, especially if shrimp farming has been accompanied by other
development activities, including the construction of canals and roads. At a
minimum, effective breaching of dikes is required. Where natural mangrove is
sparse, there may also be a shortage of mangrove propagates, in which case
mangrove nurseries may have to be established.
The possibilities for rehabilitation of degraded coastal systems were
discussed at the scientific International Workshop on the Rehabilitation of
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Degraded Coastal Systems, organized in 1998. One goal of the workshop was to
bring together key research on habitat restoration in a range of tropical habitats.
Another was to evaluate critically the effectiveness of rehabilitation and to
provide a summary of the state of the art in Asia.
Options for Rehabilitation and Restoration
However, despite these potential difficulties there are examples of
conversions to other uses, some of which may be regarded as successful. In
Samut Sakhon large tracts of abandoned shrimp ponds are being converted to
non-agricultural land use, such as for housing estate and industrial
developments. The abandoned shrimp farms can be converted to salt farms or
fish culture operations and shrimp farms located near main roads have sold top
soil for construction projects.
Apart from the fact that vast areas of mangroves are cut, another
consequence of industrial shrimp farming is that there is a vast volume of waste
produced inside the ponds by the shrimps. Food eaten by shrimps but not
retained in their body ends up as waste. As the waste piles up, bacteria flourish
and consume the available oxygen. This can suffocate the shrimps and reduce
their growth. Intermediate waste products both of shrimp, ammonia and nitrite,
are toxic to shrimp, fish and other animals. In order to avoid this problem, the
water from inside the ponds is regularly removed out and the ponds are filled in
with clean water. This system results in the pollution of the neighbouring surface
waters
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