Tài liệu STRATEGIC ENVIRONMENTAL ASSESSMENT on shrimp farms in the southeast of Thailand docx

Much of the land converted into intensive shrimp farms in the Upper Gulf Provinces of Thailand were mangrove forests, nipa palm forests, coconut groves or were used for extensive and sem

Minor Field Studies No 176

_ Swedish University of Agricultural Sciences

International Office

STRATEGIC ENVIRONMENTAL ASSESSMENT

on shrimp farms in the southeast of Thailand

Teresia Lindberg and Anna Nylander

Supervisor in Sweden:

Hans-Georg Wallentinus, Associate Professor and Director of the EIA Center, SLU,

Department of Landscape Planning Ultuna, Uppsala

Supervisor in Thailand:

Magnus Torell, Project leader at ICLARM

The Minor Field Studies series is published by the International Office of the Swedish University of Agricultural Sciences

Minor Field Studies are carried out within the framework of the Minor Field Studies (MFS) Scholarship Programme, which is funded by the Swedish International Development Cooperation Agency (Sida)

The MFS Scholarship Programme offers Swedish university students an opportunity to undertake two months´ field work in a developing country to be analysed, compiled and published as an in-depth study or graduation thesis work The studies are primarily made on subjects of importance from a development perspective and in a country supported by Swedish development assistance

The main purposes of the MFS programme are to increase interest in developing countries and to enhance Swedish university students´ knowledge and understanding of these countries and their problems and opportunities An MFS should provide the student with initial experience of conditions in such a country A further purpose is to widen the Swedish human resource base for international development cooperation

The International Office of the Swedish University of Agricultural Sciences administers the MFS programme for the rural development and natural resources management sectors

The responsibility for the accuracy of information presented rests entirely with the respective author The views expressed are those of the authors and not necessarily those of the International Office

Swedish University of Agricultural Sciences

This Minor Field Study (MFS) was performed by Teresia Lindberg and Anna Nylander, who are both studying Eco-toxicology at Uppsala University in Sweden The report is a Master´s thesis for Teresia Lindberg

The Swedish International Development Agency (Sida) finances a number of so-called Minor Field Studies for students or young people to carry out a research project in a developing country The study usually takes place in one of Sida´s target countries and is part of a local Sida-sponsored aid programme The study was located on the south east coast of Thailand with the Coastal Resources Institute (CORIN) at the Prince of Songkhla University in Hat Yai

as a study centre The field work was carried out from the end of February until the end of April, 2001

A number of people have been a great help for us during our study We would first like to thank our supervisor Hans-Georg Wallentinus at the Department of Landscape Planning Ultuna, SLU for help and support and Magnus Torell at ICLARM for providing us with very useful contacts in Thailand

At CORIN in Hat Yai we would like to thank Somsak Boromthanarat and Ayut Nissapa for letting us work at their office and for helping us with contacts

We would also like to express our gratitude to Siri Tookwinas at the Department of Fisheries

in Bangkok, Noparat Bamroongrugsa at the Prince of Songkhla University, Putth

Songsangjinda at the Department of Fisheries in Songkhla, Max Andersen at DANCED (Danish Co-operation for Environment and Development) in Ranod and Jim Enright at The Mangrove Action Project in Trang for assistance during our field study A special

appreciation to Simon Funge-Smith at FAO in Bangkok who has been a tremendously good source of information both in Thailand and when questions turned up in Sweden

Sara Gräslund at the Institute of Applied Environmental Research at the Stockholm

University and Johan Sundberg at Sida have provided us with informative material

Last, but not least our sincere thanks to all helpful and friendly Thai people and especially the shrimp farmers

This Strategic Environmental Assessment was carried out in order to collect up-to-date

material about the situation of the coastal shrimp farming industry in the south east of

Thailand and to compare different shrimp farming methods The semi-closed intensive shrimp farming system, which is the most commonly applied farming method in Thailand, is

compared with a closed farming system where the water is recirculated and a system where the sludge is removed on a regular basis The study was performed in five provinces on the southeast coast of Thailand where, during the spring of 2001, the authors interviewed shrimp farmers as well as expertise at Departments, University institutions and Environmental

organisations

The black tiger shrimp dominates the Thai production and about 90% of the cultivated

shrimps are exported for luxury consumption in industrialised countries Marine shrimp

farming has expanded greatly during recent decades and can today be found in every coastal province of the country The intensive farms have been constructed by converting a variety of land uses, including former extensive shrimp farms, mangroves, rice paddies and other

plantations

The environmental and socio-economic impacts of the different shrimp farming systems are described in the report and the alternatives are evaluated and compared with each other with reference to the different impacts The main environmental impacts are due to chemical use, mangrove destruction, salinisation, eutrophication, sedimentation, extraction of ground water and spread of diseases and genes The socio-economic impacts are, for example, health

problems, loss of livelihood and fresh water resources, impacts on agriculture, marginalisation and changes in employment

According to the comparison, it is apparent that the semi-closed system has the most negative environmental and socio-economic impacts Both the closed recirculating system and the sludge removal system have less negative impacts on the environment and on the social and economic systems than the semi-closed farming system Concerning mangrove forest

destruction, extraction of ground water and loss of mangrove values and products, the

alternatives give no impact at all

The closed recirculating system is considered to be the most sustainable alternative due to the many issues where no negative impacts occur This is only true providing that the system is successful despite some managerial problems If the system should not work entirely, the sludge removal system or a closed recirculating system without waste water recirculation are still much more sustainable alternatives than the semi-closed farming systems that are used in Thailand presently

The major problems connected to the two alternative methods described in this report are the high construction and operation costs It is not realistic to expect a poor farmer to adopt one of the alternative systems described in this report without external economic support A

reasonable possibility for a farmer could be to continually invest in more sustainable methods

Keywords: Shrimp farming, aquaculture, ecotoxicology, strategic environmental assessment,

environmental impacts, socio-economic impacts, intensive shrimp farming, chemicals,

mangrove forest, Thailand

1 INTRODUCTION 4

1.1 Objectives 4

1.2 Methodology 4

2 SCOPE 5

3 DEFINITIONS AND GLOSSARY 7

4 HISTORY 11

5 PRESENT STATUS OF SHRIMP FARMING IN THAILAND 13

6 ENVIRONMENTAL SETTINGS 16

6.1 Black tiger shrimp (Penaeus monodon) 16

6.2 The natural cycle of shrimp development 16

6.3 The mangrove forest 16

6.4 Hatcheries 18

6.5 Grow-out techniques 19

6.6 Inland shrimp farming 21

6.7 Production process and water treatment 21

6.8 Diseases of cultured black tiger shrimp 23

6.9 Artificial shrimp feed 24

6.10 Chemicals and biological products 25

7 DESCRIPTION OF THE ALTERNATIVES 28

7.1 Zero alternative: Semi-closed intensive system 28

7.2 Alternative 1: Closed recirculating system 29

7.3 Alternative 2: Sludge removal system 30

8 ENVIRONMENTAL IMPACTS 31

8.1 Mangrove deforestation 31

8.2 Physical barriers 32

8.3 Pollution by chemicals and water treatment products 33

8.4 Sedimentation 34

8.5 Salinisation and the extraction of groundwater 35

8.6 Eutrophication and water quality issues 37

8.7 Energy usage 39

8.8 Diseases and genetic pollution 40

8.9 Trawling for wild brood stock and for fish meal 41

8.10 Decreased need for trawling wild shrimp 42

9 SOCIO-ECONOMIC IMPACTS 43

9.1 Land conversion and loss of livelihood 43

9.2 Employment and inequity 44

9.3 Public health problems 45

9.4 Impacts on the agriculture 47

9.5 National versus local economy 48

10 EVALUATION OF THE ALTERNATIVES 50

10.1 Evaluation of the alternatives concerning environmental impacts 50

10.2 Evaluation of the alternatives concerning socio-economic impacts 52

11 CONCLUSION AND DISCUSSION 55

12 MITIGATION 57

13 SUSTAINABILITY ISSUES 62

14 UNCERTAINTIES 65

15 REFERENCES 66

APPENDIX 1 GOVERNMENT REGULATIONS AND PLANNING 72

APPENDIX 2 CHEMICALS COMMONLY USED IN THAILAND 76

APPENDIX 3 DIRECT AND INDIRECT PRODUCTS FROM THE MANGROVE FOREST 78

to assist the Swedish International Development Cooperation Agency, Sida, in their

investigation of possible future support to shrimp farming

The present work is part of a larger study on shrimp farming, which is being performed by the EIA-centre at SLU on behalf of Sida One of the goals with this study is to be able to set up a checklist for review of Environmental Impact Assessments (EIAs), including SEAs, for shrimp farming EIAs are always needed in project proposals, which are submitted to Sida for assessment Both the Rio Declaration and the Agenda 21 emphasise the importance of using EIAs in development co-operation

A purpose of this SEA is to add to Sida´s EIA-handbook The report can hopefully also be used to facilitate and improve the EIA-process for project directors and consultants

1.2 Methodology

The study includes interviews with shrimp farmers and with expertise at Departments,

University institutions and Environmental organisations Employees at feed processing

factories and independent researchers were also interviewed Most of the shrimp farms were family-owned, but some were big shrimp farming companies such as Chareon Pokphand (CP-company) or research farms like the DANCED funded shrimp farm in Ranod and the Department of Fisheries shrimp farm in Songkhla Field observations and literature studies were also performed in this study

The material is summarised and compared in a Strategic Environmental Assessment (SEA) This report is a back-casting SEA, which means that it investigates the impacts of already existing shrimp farms

Environmental Impact Assessment (EIA) is a process that examines the environmental

consequences of development actions in advance EIA is also a document that should describe and compare different alternatives The zero-alternative, which describes the situation

providing that nothing changes in the future, should be included in the comparison An EIA shall take into consideration direct or indirect effects on:

• People, flora and fauna

• Land, water, air, climate and landscape

• Material assets and cultural heritage

• Interaction between the above-mentioned factors

The assessment how a project relates to environmentally sustainable development should be performed in a holistic perspective Therefore, equally environmental, health-related, social and economic aspects should be considered

SEA is a relatively new tool and has not yet been so widely applied in practice Therefore there is no determined, defined method for how a SEA should be prepared and applied While EIAs are made for specific projects, Strategic Environmental Assessments are used for

programmes, policies and plans that are loosely structured and that are continuously reformed

A SEA has more diverse angles of approach than an EIA and the work takes place on an

all-embracing level A project EIA deals, for example, first with the question how a project or an activity shall be worked out, while a SEA concentrates on the questions if various projects are suitable to carry through and if so where they are to be located Even the question why can be

important to raise (Naturvårdsverket, 2000)

In addition to what has been written on EIAs above, the SEA should, according to Sida, include (Sida, 1998):

• A description and analysis of the environmental situation in the sector/region in question

• A description and analysis of environmental work in the sector, including legislation and environmental regulations

• Other relevant information on the institutional situation

• An analysis of the combined effects of different activities/measures in the

In this report three different shrimp farming systems are discussed and compared closed intensive shrimp farming is the most common method in Thailand today and is

Semi-therefore the zero-alternative This alternative is divided into two examples: zero-alternative

A that is situated in a coastal area far away from the mangrove forest and zero-alternative B that is located in a mangrove area The two other alternatives are the closed, recirculating system and the sludge-removal system Both these systems are under development It is concluded that a combination of these two alternatives is not economically possible, even though it might be more sustainable

The geographical constraint is the southeast coast of Thailand That includes five provinces: Surat Thani, Nakhon Sri Thammarat, Pattalung, Songkhla and Pattani (Figure 1) The focus of this report is on environmental impacts To a certain degree we have also evaluated social and economic impacts This document focuses on coastal shrimp farming However, inland

shrimp farming is an important issue in Thailand The activity still proceeds although the activity was banned in Thailand in 1998 Therefore, this shrimp farming method is not included in the impact assessment Related industries such as hatcheries and processing factories are issues that are too large to be evaluated within the allowed time frame The construction phase in shrimp farming is only mentioned briefly in the report

Our time perspective is about ten years, since a common shrimp farm in Thailand today can

be operated during a maximum of this time

Figure 1 A map showing the geographical constraint of the study.

The provinces included in the study are Surat Thani, Nakhon Sri

Thammarat, Pattalung, Songkhla and Pattani.

3 Definitions and glossary

Abandoned shrimp farm In this report, the term abandoned refers to a shrimp

farm that is out of production

Anaerobic decomposition Decomposition without the presence of oxygen

Antibiotic resistance Overuse of antibiotics may lead to the development of

resistant strains of micro-organisms

Alkalinity Alkalinity is the measure of the total amount of

calcium, magnesium, potassium, phosphorus, boron, silicon and others The purpose of knowing the alkalinity is to understand its ability to neutralise acids

Aquaculture Farming of aquatic organisms including fish,

molluscs, crustaceans and aquatic plants

Baht The Thai currency (In the spring of 2001,

45.7 baht = 1 US$.)

Bioaccumulation An increased concentration of chemicals in an

organism

Biomagnification The result of biomagnification is that animals at the

"top" of their food chain have higher contaminant levels than animals at the "bottom" The compounds accumulate in the bodies

Black tiger shrimp A shrimp species that is named for its big size and

banded tail

offspring

Calcification Shell production, making the shell hard by taking up

calcium

Cation A positively charged ion

Chemical residue The remains of a chemical compound, in this case in

the shrimp body

Closed system The water in the grow-out pond is held in the pond

during the whole grow-out period Only at harvest the water is released Even though seepage occurs it is a closed system

Crustaceans An animal class that includes shrimp, crab and lobster

etc

nitrogen oxides, sulphur oxides, partially combusted

hydrocarbons and soot particles.

cows

Ectoparasites Parasites, that live on the outside of its host´s body

Extensive shrimp farm See the chapter “Grow-out techniques”.

Greenhouse gas A gas that absorbs infrared radiation, and causes the

greenhouse effect (Carbon dioxide, chlorofluorocarbons, ozone, methane and nitrogen oxides)

Immunostimulants Products that stimulate the immune system as well as

kill bacteria

Intensive shrimp farm See the chapter “Grow-out techniques”

Inland shrimp farm Inland refers to the land beyond brackish water areas

with zero or near zero salinity in the soil The brackish

or marine water has to be trucked in from the sea

Juvenile Young organism

post larva

Open intensive system See the chapter “Grow-out techniques”

Pathogens Disease-developing bacteria, virus, fungi or protozoa

Pesticide Any chemical compound used to kill pests that destroy

agricultural production or are in some way harmful to humans

Phytoplankton The photosynthesising plankton organism

Post larvae The last stage of shrimp development before reaching

adult size

freshwater species In common language big “shrimps” are often called prawns

Prophylactic Preventional

harmful bacteria by introducing “good” bacteria

Protozoan A group of unicellular or acellular organisms

treaty adopted on 2 February 1971 in the Iranian city of Ramsar

Self-pollution The re-use of pond water after water discharge

Semi-intensive shrimp farm See the chapter “Grow-out techniques”

Shrimp According to FAO terminology, shrimp refers to

marine and brackish species In common language small “shrimp” are often called shrimp

Shrimp carapaces The shell of the shrimp

Trickle-filter A biological filter used for treatment of pond water

The bacteria on the filter feed on ammonia

organisms in surface waters of the world They occur in both marine and freshwater habitats and in associations with aquatic animals

Wetland Areas of marsh, fen, peatland or water, whether natural

or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas

of marine water the depth of which at low tide does not exceed six meters

4 History

Traditional extensive shrimp farming first began around 1935 in Rayong and Chanthaburi provinces east of Bangkok Rice farmers in mangrove areas were experiencing low yields because of saltwater intrusion into the rice paddies Under low-tide conditions the farmers harvested shrimp for domestic consumption and for the local market The good prices for shrimp and the optimal brackish water encouraged farmers to convert their rice fields into shrimp ponds A major expansion in extensive shrimp production took place in 1947 when the price of salt fell drastically Many small-scale salt producers in the coastal provinces

southwest of Bangkok transformed their salt fields into shrimp farms because of higher profit (Flaherty and Karnjanakesort, 1995)

By the late 70s the introduction of hatchery technology made it possible for farmers to adopt semi-intensive production methods in which hatchery-reared seed supplemented wild fry In

1973, the Department of Fisheries (DOF) began to promote semi-intensive marine shrimp culture A shrimp fry hatchery was constructed by the Department of Fisheries to provide mainly black tiger shrimp to small-scale producers (Flaherty and Karnjanakesort, 1995)

In the early 80s Taiwan was the first country to transform traditional extensive shrimp

cultivation into intensive farming of the Black tiger shrimp and became the leading shrimp producing nation in the world Other Southeast Asian countries followed the Taiwanese example and in many countries this development was supported by international financial organizations such as the World Bank and the Asian Development Bank (Patmasiriwat et al., 1998) In the mid 80s, intensive shrimp farming became abundant in the Upper Gulf

Provinces of Thailand The exploding growth started with increasing export prices for shrimp, particularly to Japan, and with a regional decrease in the catch of wild shrimp Another factor that contributed to this rapid growth was the large decline in the Taiwanese production due to problems with diseases (CORIN, unpublished) Disease problems among cultured shrimp producers in Taiwan resulted in a 70% scale-down in production in 1988 and an even more drastic cut in 1989 The fact that the Taiwanese farmers were gradually willing to share some

of their technology and expertise further contributed to the exploding growth in Thailand (Flaherty and Karnjanakesort, 1995)

Much of the land converted into intensive shrimp farms in the Upper Gulf Provinces of

Thailand were mangrove forests, nipa palm forests, coconut groves or were used for extensive and semi-extensive shrimp farming The people who started the intensive farms had little or

no knowledge of shrimp farming During 1989-1990 an estimated 45 000 ha of shrimp farms

in the northern part of the Gulf were abandoned due to consistent crop failures (Funge-Smith and Stewart, 1996) The disease outbreaks that destroyed the crop were due to stress created

by the poor water quality in the Inner Gulf of Thailand Not only self-pollution by the farms but also urban, industrial and agricultural waste water carried by some of Thailand’s major rivers caused the problems Intensive shrimp farming moved to the eastern provinces towards the Cambodian border and to the southeastern coast of Thailand, due to the pollution in the Inner Gulf Area Finally, shrimp farms started to appear in the upper southern provinces of both the east coast and the west coast The farms were established in public mangrove forests and in areas of poor paddy land along the coast (CORIN, unpublished) These provinces were more suitable for shrimp farming than the Upper Gulf Provinces because of their location away from industrial and urban pollution and because they could receive water directly from the sea rather than through common canals

Between 1987 and 1991 a major intensification of production took place in Thailand and the annual shrimp production rose by 615% (Flaherty and Karnjanakesort, 1995) Since 1990, cultivated shrimp production has exceeded the production of captured shrimp (Patmasiriwat, 1998) In 1991, Thailand became the largest producer of shrimp in the world and still is (CORIN, unpublished)

In 1995-97 there was a huge outbreak of disease in Thailand Water quality deteriorated,

production dropped dramatically and many farmers had to abandon their farms In 1994, some

provinces in Thailand (for example, Ranong province) lost as much as 90% of their

production for at least one of the crops during the year (Funge-Smith and Stewart, 1996) During the summer of 1997, the Thai economy collapsed and the government floated the currency Since Thai shrimp are usually sold on the international market in dollars, the

effective price of Thai shrimp doubled For a period of about eight months in 1997 to 1998, profits from the shrimp farms exploded (Rosenberry, 2001)

The shrimp industry in Thailand had a rough year in 1996 due to impacts of shrimp disease, environmental problems, increased production costs, a low Japanese yen and an USA

embargo on trawled shrimp The fall of the Japanese yen in 1996 caused an 18% decrease in the export of frozen shrimp from Thailand to Japan The USA imposed a ban on Thai trawled shrimp caught without a turtle excluder device The Thai officials claimed that they provided their shrimp fishermen with the device Eight months later, when Thailand was believed to have fulfilled the requirement, the ban was lifted

By 1998, a clear pattern of disease had developed in Thailand: White Spot Disease (WSD)

tended to hit during the northeast monsoon (October to January) and Vibriosis tended to hit during the hot season (March and April)

Inland or fresh water shrimp farming depends on low salinity techniques developed in the 90s The spread of diseases along the coastal area and shortages of suitable locations along the coast encouraged shrimp farmers to move inland Low salinity shrimp culture techniques also developed to overcome the seasonal constraints and evolved through a process of

experimentation by small-scale farmers and hatchery owners The collapse of the Thai

economy encouraged the rapid expansion of shrimp farming in Thailand’s central region Competition between shrimp farming and other interests, such as tourism and industrial development elevated the cost of coastal land, which further contributed to the rapid

expansion (Flaherty et al., 1999) Once the technical possibility and economic capability of Black tiger shrimp culture under low salinity conditions established, inland shrimp farming expanded rapidly (Flaherty et al., 2000) The Thai government banned the inland shrimp farm practices in 1998, causing a lot of conflicts between shrimp farmers and rice farmers Fishery officials have sometimes refused to enforce the ban since they have earlier invested in the shrimp business Many farmers have also refused to comply with the ban (CORIN,

unpublished)

5 Present status of shrimp farming in Thailand

Thailand is a tropical country in Southeast Asia with a population of about 60 million people and a total land area of 514 000 sq.km The country borders to Malaysia, Lao PDR, Myanmar and Cambodia Thailand has two long coastal lines, one along the Gulf of Thailand (1870 km) and one along the Andaman sea (800 km)

Today, Thailand is one of the leading tourism destinations in Southeast Asia Foreign tourists visiting Thailand have increased from about 1.2 million in 1975 to roughly 9.5 million in

2000 In 1990, tourism produced about 4 billion US$, only half this income is generated from the shrimp industry (Huitric et al., 2000) Tourism not only brings good to the country, there are problems with, for example, garbage and pollution Rice has been the largest single

foreign exchange earner for more than a century in Thailand; rice exports being in the

forefront of Thailand’s economic development Even though Thailand now has an

industrialised economy, more than 59% of the country's working population is engaged in agricultural production Thailand is still the biggest rice exporter in the world, earning 1.7 billion US$ in 1996 (Flaherty at al., 1999)

The Gulf of Thailand is located to the west of the South China Sea The Gulf is a

semi-enclosed and relatively shallow sea with a mean depth of 45m and covering a total area of roughly 320,000 sq.km Numerous rivers discharge freshwater, sediments and polluting substances into the Gulf The low salinity water of the Gulf is even more diluted by rain and freshwater runoff Cool and saline water flows into the Gulf from the South China Sea

Rainfall, tidal currents and monsoons create movements in the water, these activities control the salinity and turbulence of the Gulf Monsoons also control the surface currents of the Gulf, being clockwise during the southwest monsoon and anti-clockwise during the northeast monsoon

The areas around the Upper Gulf of Thailand have little water circulation and are actually not really suitable for aquaculture, since effluents from shrimp farms, industries and households are in a "closed area" On the contrary, the areas along the Lower Gulf and the Andaman sea are facing the open sea and therefore have good water circulation and are more suitable for aquaculture Around the Gulf there are millions of people receiving their livelihood from fish and mineral resources from the Gulf Many more people are affected by changes in the

environment of the Gulf, both if the changes are physical or political

Southern Thailand stands for 40% of Thailand´s shrimp culture (Thongrak et al., 1997) Along the southeast coast, shrimp farms are densely located on a strip of coastal land about 1-

2 km wide (Figure 1) which measures about 700 km north to south (Rosenberry, 2001) Shrimp farm ownership along the coast is a mix of corporate, contracted and small-scale independent farmers The small-scale farms are by far the most abundant in this area

(Vandergeest et al., 1999) They are often situated along canals that are flushed by tides and that flow parallel to the coast The closeness of the canals keeps the infrastructure costs low Shrimp farms taking water directly from the sea are likely to be larger or corporate The CP-company and Aquastar are two corporations that have set up contracted farming in the southeast of Thailand

In shrimp farms in the south of Thailand there are four basic soil types: clay, lateritic,

mangrove clay and sand Soil types vary a lot between different shrimp farming areas For

example, in Ranod there is mostly low organic content soil (91%) but also some sand or sand/clay (5%) and mangrove clay (4%) In Nakorn Sri Thammarat, where mangrove forests are abundant, the soil type is therefore mostly mangrove clay The soil type is an important factor, since it affects the pond environment The soil types affect the accumulation of

sediments in the pond, the amount of organic matter, water seepage, acidity and the ease of phytoplankton management Shrimp farms are often constructed on land with low agricultural potential and therefore the costs are low (Funge-Smith and Stewart, 1996)

Marine shrimp farming has expanded and can today be found in every coastal province of the country In 1995, there were about 26 000 shrimp farms in Thailand (Patmasiriwat et al., 1998) and 40% of the area along the coast in southern Thailand is used for shrimp farming Farms have been constructed by converting a variety of land uses, including former extensive shrimp farms, mangroves, rice paddies, orchards and coconut and rubber plantations

(Table 1)

Table 1 Previous land use before shrimp farm development in the south of Thailand

Previous land use Percent of farms

surveyed

Fruit, vegetable or other agriculture 27.5

Mangrove / Wetland 13.7

Uncultivated land / Wasteland 5.9

Extensive shrimp farms 3.9

(Source: Funge-Smith and Stewart, 1996)

The mangrove forests cover about 936 km or 36% of the 2 600 km long coast of Thailand About 75-80% of the mangrove forest is situated on the west coast along the Andaman sea Mangrove forests are situated in all 12 provinces in the south of Thailand In 35 years from 1961- 1996, about 50% of the mangrove forest was destroyed in the country (Platong, 1998) The main causes for the destruction are conversion to shrimp farms, mining, forestry and agriculture About 30% of the mangrove destruction is due to shrimp farming (Tookwinas, pers comm., 2001)

About 95% of all shrimp farmers in Thailand today are operating intensive systems, only a few extensive farms are left and nearly no semi-intensive farms exist Today, there are 95% coastal farms and 5% inland shrimp farms in Thailand (Tookwinas, pers comm., 2001) Even though there is a ban against inland shrimp farming, the farming method is predicted to grow

in the future (Enright, pers comm., 2001) Most of the intensive shrimp farms are semi-closed and only a few farmers still use open systems (Tookwinas, pers comm., 2001)

It has been estimated, and made a national policy in Thailand, that shrimp farming areas should not exceed 76 000 ha The only legal possibility to establish new farms in Thailand today is to reuse old, abandoned shrimp ponds (Tookwinas, unpublished) During 1993 there were 72 000 ha of shrimp ponds in Thailand (Patmasiriwat et al., 1998) Only about 60% of the shrimp farms in Thailand are registered at present, the remainder of the ponds are illegal (Tookwinas, pers comm., 2001) The regulations for shrimp farming are often ignored About 80% of the shrimp farms in Thailand are small family-owned farms where the farming area is between 0.16-1.6 ha (Tookwinas and Thanomkiat, unpublished) The average farm size in Thailand is 2 ha according to Mr Tookwinas Most farms in Thailand are independent, only 1% of the farms tend to be contracted by larger companies (Tookwinas, pers comm., 2001)

Most of the hatcheries are also small and family-owned These so-called backyard hatcheries stand for more than 80% of the national shrimp fry (Tookwinas, 1995) The hatcheries depend

on wild spawners from the Andaman sea, since a reliable cultivated source of Penaeus

monodon broodstock has not yet been developed in Thailand (Flaherty et al., 2000)

About 70% of the shrimps produced in Thailand are cultivated and the rest are trawled

(Tookwinas pers comm., 2001) According to Sida, the majority of the coral reefs in the Thai Gulf are destroyed at the present time (Sida, 1997) The destruction of corals is not only due

to trawling but also due to the discharge of wastewater from communities and industrial plants, pollution from aquaculture and due to incorrect fishery gear like explosives and

poisons for fishing Other activities damaging the coral reefs are tourist boats using the reefs for anchorage and breaking the corals for souvenirs

Approximately 90% of the cultivated shrimp are exported (Tookwinas, pers comm., 2001) Cultivated shrimp is the third biggest export by value in Thailand In 1999, over 2 billion US$ were generated from the Black tiger shrimp industry in Thailand and the country had an annual production of about 200 000 tonnes (The Nation, 2001; Gregow and Zetterström, 2000) The biggest importers of Thai shrimp are USA, Japan, the European countries, Taiwan and Canada Last year (2000) the USA imported 114 727 tons, which is about one-third of the total import of shrimp The EU-countries only imported 15 519 tons of Thai shrimp in year

2000 This low figure is mainly due to the increase in import tariffs following the loss of Thailand’s status under the Generalized System of Preferences (GSP) According to the GSP, less-developed countries have the benefit of having lower tariffs When the less-developed countries share of the EU market reaches a certain level it loses this benefit The amount of Thai shrimp imported to the EU has declined by 60% since the GSP privileges from 18 Thai products were removed in 1999 EU import tariffs on Thai shrimp are nearly four times higher than on shrimp from countries such as Ecuador, Colombia and Peru, which face a much lower import tax (Bangkok Post, 2001) In year 1998, 375 tons of Black tiger shrimp were imported

to Sweden (Gräslund, pers comm., 2001) The Swedish Society for Nature Conservation has requested for a boycott against Black tiger shrimp (Dagens Nyheter, 2000)

Chemicals and drugs are widely used in shrimp culture for prevention or treatment of

diseases, to be used as disinfectants and pesticides, or for soil and water treatment The use of chemicals and antibiotics has decreased during recent years according to Tookwinas (pers comm., 2001) Intensive shrimp farming has introduced a wide variety of side industries at different stages of the shrimp production: feed and chemical manufacturing industries,

hatcheries, cold-storage factories, processing industries and exporters (Huitric et al., 2000) Today, approximately 2 million people are employed in the shrimp farming industry

(Tookwinas, pers comm., 2001) Depending on the farm size, farmers are sometimes hired to manage the ponds These workers often live and work at the farms

6 Environmental settings

6.1 Black tiger shrimp (Penaeus monodon)

The Black tiger shrimp (or Giant tiger shrimp) is named for its huge size and banded tail and

it dominates the production everywhere in Asia except in Japan and China (Rosenberry, 2001) The shrimps are generally found from near shore shallow waters to as far as 100 km off shore at depths greater than 100 m (ASCC News, 1996) It accounts for more than half of the total output of world shrimp aquaculture The black tiger shrimp is the largest and fastest growing farmed shrimp It can reach a size of 360 mm and weight over 150 g The shrimp can tolerate a wide range of salinities, but is highly susceptible to two of the most lethal shrimp viruses: Yellow Head Disease (YHD) and White Spot Disease (WSD) There are often

shortages of wild broodstock and captive breeding is difficult The black tiger shrimp is a very popular luxury food in Japan, USA and Europe (Rönnbäck, 2001)

6.2 The natural cycle of shrimp development

In the wild, shrimps mate in the open sea After 15 to 20 days the females spawn

approximately 500 000 to one million eggs directly into the sea The larva develops through

12 stages of nauplius, protozoa and mysis before metamorphosing into a post-larva (Figure 2)

In these stages of rapid growth, the shrimps migrate from the open sea to the estuaries When the shrimp has reached the post-larval stage it enters the estuaries, seeking for shallower, often less saline waters where it can find abundant food In the nutrient-rich mangrove forest the shrimps develop into juveniles They later return to the sea once again for mating The natural life span of black tiger shrimp is normally 1-1.5 years, whereas they reach sexual maturity in about 10 months (Tobey et al., 1998)

Figure 2 The life cycle of the Black tiger shrimp (ASCC, 1996)

6.3 The mangrove forest

The mangrove forests are found along sheltered tropical and subtropical shorelines of Africa, Australia, Asia, and America and act as barriers between land and sea Mangrove forests are comprised of taxonomically diverse halophytes (salt-tolerant plant species), which grow in the inter-tidal zones of the tropics Mangrove trees have adapted aerial, salt-filtering roots and salt-excreting leaves that allow them to cope with the saline environment in the wetlands where other plant species cannot survive (Figure 3) Mangroves vary in height according to

species and environment, from mere shrubs to 40 m high trees Certain plant species occupy particular areas, or niches, within the ecosystem at various distances from the sea The

composition of species occurring in a zone depends on how often the zone is covered by the tide, how salty the soil is and how much fresh water that is available (Platong, 1998)

Figure 3 Mangrove roots.

In Chapter 8 the values of the mangrove forest and the impacts of the destruction of the mangroves are described in greater detail In short, the values of the mangrove forest can be summarised as follows The mangrove forest:

• provides nutrients for the marine environment and supports complex food webs

• creates breeding habitats and restrictive impounds that can offer protection for maturing offspring

• supports other ecosystems like mudflats, sea grass beds and coral reefs

• filters nutrients and traps pollutants and thereby improves the water quality

• protects the coastal areas from erosion, storm damage, and heavy winds by stabilising the sediments

• has a high conservation value because of its huge biodiversity

• has a high potential value due to the vast genetic resources that can be found there and can

be used in the production of drugs and chemicals

• supplies the coastal communities with food, medicines, fuel wood and construction

materials (table, appendix 3)

• provides many commercially important products (table, appendix 3) like charcoal, paper, textile, leather, tannins and seafood

Mangrove forests are among the most threatened habitats in the world and are disappearing at

an accelerating rate The forests are suffering from pollutants, attacks by parasites and

prolonged flooding from artificial dikes, etc In addition, the charcoal and timber industries as well as urbanization, agriculture, aquaculture and tourism have severely impacted mangrove forests Also over-exploitation by traditional users and mining, whose dominant effect is deposition of sediments, have greatly affected the mangrove forest The rapidly expanding shrimp aquaculture industry is today a great threat to the mangroves both through

deforestation and through sedimentation and pollution from the waste water from the ponds Globally, shrimp farming may be responsible for between 10 and 25% of the mangrove clearing since 1960 (Tobey et al., 1998) and in Thailand for about 30% (Tookwinas, pers comm., 2001)

Traditionally, shrimp farming was initiated in mangrove areas These extensive farms

depended on the tide to bring in seed and feed into the pond It is today recognized that

mangroves are unsuitable for semi-intensive and intensive ponds because of the acid sulfate soils (Tobey et al., 1998) Additionally, the mangrove soil is very soft and contains plenty of roots and stumps and consequently is not suitable for pond construction

According to Plathong (1998), the dramatic decrease in mangrove forest in southern Thailand has been attributed mainly to conversion to shrimp farming Mangroves along the east coast

of southern Thailand have, though, been converted for various land-uses such as salt ponds, shrimp ponds, coconut plantations, paddy fields or buildings According to John Hambrey (The Mangrove Questions), Funge-Smith (pers comm., 2001), and others, shrimp farming is only one of many pressures on the mangrove and rarely the most significant There is

confusion concerning the definition of mangrove because different countries use different definitions Should the non-flooded secondary forest behind the mangrove forest be defined as

a mangrove? To date most intensive shrimp farm developments have taken place in this flooded area or in salt marshes In contrast, extensive shrimp ponds are typically built in the flooded parts of the mangrove Figures blaming the shrimp industry for the destruction of about 30% of the mangrove forest in Thailand often refer to this secondary forest behind the primary mangrove Additionally, pristine mangrove forests are very rarely destroyed in

non-Thailand at the present time Most of the mangrove in non-Thailand today is young because of intense charcoal harvesting some decades ago and therefore the conservation value of this young forest is questionable (Funge-Smith, pers comm., 2001)

6.4 Hatcheries

To cope with the high demand for post-larvae in Thailand, hatcheries have become a great industry in the country Actually, all post-larvae in Thailand are hatchery-produced from wild broodstock (Funge-Smith and Stewart, 1996) This causes high pressure on the fishing for these wild shrimp The hatcheries sell two types of products: nauplii (tiny, newly hatched first stage larvae) and post-larvae Nauplii are sold to specialists who grow them to the post-larval stage Post-larvae are stocked in nursery ponds or directly in grow-out ponds

Gravid shrimp are either captured in the wild or matured in the hatchery The shrimp spawn in the dark, so through photoperiod manipulation they can be induced to spawn at any time Eye ablation (cutting off one eye from the female) to initiate spawning in the female shrimp is common in Thailand today This results, however, in a rapid death for the shrimp and thereby this method is less sustainable than the one for pond-reared brood stock (Funge-Smith and Stewart, 1996) One day after spawning the eggs hatch into nauplii These metamorphose into zoeae after a couple of days and then into myses, which is the third and final larval stage This stage lasts another three or four days and then the myses metamorphose into post-larvae Post-larvae look like small adult shrimps and feed on zooplankton, detritus and commercial feeds The entire process from hatched eggs to post-larvae lasts approximately 18 - 20 days

(Rosenberry, 2001)

Post-larvae may be placed in nursery ponds where they are cultured for 30 - 45 days before being placed in grow-out ponds The grow-out ponds are the only ponds that can produce harvest-sized shrimp Therefore these ponds should be cycled as frequently as possible during the growing season This is facilitated by the use of nursery ponds This technique is called

"staging" and facilitates the feeding and counting of the shrimp (Tobey et al., 1998)

6.5 Grow-out techniques

The long coast line of Thailand and the tropical climate provide ideal conditions for round shrimp culture Marine shrimp farming systems can be classified into three categories

year-of intensity: extensive (traditional), semi-intensive and intensive farming systems The

different types are classified in terms of cultured area and stocking density

Extensive culture

The extensive shrimp farming system is primarily used by farmers in areas with limited infrastructure, few trained aquaculture specialists, inexpensive land and high interest rates The ponds are located along bays and tidal rivers and are constructed by the accumulation of elevated mud walls around the bottom of the ponds The trapped larvae are prevented from returning to the sea with the withdrawal of the tide by a screen placed in the sluice of the wall When local waters are known to have high densities of young shrimp, the farmer opens the gates of the pond, captures the wild shrimp and grows them to market size (Tobey et al., 1998)

Several species coexist together in the pond and producers rely on the tide for water exchange (0-5% water exchange per day) and to bring in seed and food (Rosenberry, 2001) Survival and yield are low in extensive culture, as are costs and risk The density of shrimp is 2 – 5 shrimp per m2 (Dierberg and Kiattisimkul, 1996) in traditional farming and the ponds are large (5-10 ha) The farms have few inputs and are mostly family-owned Extensive pond enclosures have an irregular shoreline, the depth is variable but shallow and there may be a considerable amount of vegetation left in the pond The extensive shrimp farms are often established in mangrove swamps or in salt flats, because the conditions for more intensive culture are poor in these areas In some cases, fertilisers or manure are added to promote algal growth Disease outbreak is rare because of the low densities Most of the extensive farms in southern Thailand are located in Nakhorn Sri Thammarat (Tookwinas and Thanomkiat, unpublished)

Semi-intensive culture

Semi-intensive shrimp farms are conducted above the high tide line The stocking densities are higher (5 – 10 shrimp per m2) than the natural environment can sustain without additional input of, for example, feed (Dierberg and Kiattisimkul, 1996) The ponds are smaller (1-6 ha) than the ones used in extensive culture and are more regular in shape (Tookwinas and

Thanomkiat, unpublished) This leads to better control over the grow-out environment The ponds have dikes and are easier to harvest than the extensive farms Nursery ponds are often used In semi-intensive shrimp farming, pumping systems and sometimes aerators driven by diesel or electrical energy are used to regulate the water exchange and to bring oxygen to the bottom of the pond The daily water exchange rate is 0 – 25% (Rosenberry, 2001) Skilled management and labour is needed and the farm depends on purchased feed and seed stock The shrimps are fed both with natural food and purchased shrimp feed According to

Tookwinas (pers comm., 2001), there are hardly any semi-intensive shrimp farms in Thailand

at the present time

Intensive culture

In intensive shrimp farming the ponds varies in size from 0.16 to 1 ha (Tookwinas and

Thanomkiat, unpublished) The intensive system demands around the clock management There are greater inputs of operating capital, equipment, skilled labour, feed, nutrients,

chemicals, drugs and antibiotics The shrimp are fed up to five times daily supplemented with

vitamins and minerals The ponds are aerated with the use of paddle wheels The stocking

densities are high (30 – 60 shrimp per m2) In intensive shrimp culture, there are 2 - 3 harvests

per year and water exchange rates can be as high as 40% daily (Dierberg and Kiattisimkul,

1996) Usually, intensive systems are coupled to their own hatcheries and nursery ponds The

risk of disease is high and a whole crop can be lost in hours There are different types of

intensive cultivation systems: open, semi-closed, closed and super-intensive systems

Open intensive systems

Traditionally, water quality has been maintained in shrimp production through the use of a

high rate of water exchange to flush excess plankton and nutrients out of the pond The open

intensive ponds require large amounts of daily water exchange to maintain suitable water

quality

Semi-closed intensive systems

Due to increasing farm density, deteriorating influent water quality and the rise in viral

diseases, there has been increasing resistance amongst farmers to the use of high water

exchange In semi-closed farming systems there is no water exchange during the first month

of production (except for compensation of evaporative loss) due to the high risk of disease

during this time A limited water exchange commences during the second month of

production

Closed intensive systems

In fully closed intensive shrimp farming there is no water exchange to the outside at all during

the whole production period Water is only added for compensation of evaporative loss and

seepage In most closed systems, water is discharged to the environment at harvest Some

closed intensive farms, however, treat and recirculate the water at harvest and thus have zero

water exchange systems

Super-intensive systems

Super-intensive shrimp farming is still in its experimental stages It requires huge amounts of

water, around 50% daily water exchange and can produce yields of 10-100 t/ha/year

(Rönnbäck, 2001) Super-intensive production requires huge investments in technology,

equipment, staff expertise and overall management Generally, these farms have problems

with management, diseases, crop failures, water quality, finances and the environment

(Rosenberry, 2001)

Table 2 Percentage water exchange in different shrimp production systems in southern Thailand

Percentage water exchange (% per month) Month of

production

Open system (clay soil)

Open system (mangrove soil)

Semi-closed system

6.6 Inland shrimp farming

The establishment of low salinity shrimp farms in areas far inland from the coast has greatly contributed to maintaining the high production of shrimp in Thailand Low salinity shrimp farming relies on salt water trucked in from the coast The farms are established in

predominating rice-growing areas, 100 km or more inland from the coast (Flaherty et al., 2000) When low salinity shrimp culture techniques developed in the nineties the shrimp

species Penaeus monodon was used for reasons of familiarity and availability This species is

well known for its tolerance to variations in temperature and salinity The development of low salinity shrimp farming was dependent on the availability of suitable shrimp post-larvae that had been acclimatized to low salinity levels (Flaherty et al., 1999)

The largest concentration of inland shrimp farms is in the lower central plain of Thailand, where rice paddies are widespread It is not surprising that low salinity shrimp farming

evolved in traditional rice-growing areas In these areas there are plenty of water supplies, which are critical to the success of shrimp farming Additionally, the irrigation infrastructure that was originally developed for rice cultivation is easy to adapt to shrimp farming The primary difference between inland and coastal farming is the salinity level in the grow-out pond The salinity in coastal shrimp ponds varies between 10-30 ppt and in inland shrimp ponds between 4-10 ppt The standard grow-out period for inland culture systems is relatively short, 120 days This is because the falling salinity levels, due to the continual addition of freshwater in the ponds, have negative effects on shrimp health and development (Flaherty et al., 2000)

The most serious impact from inland shrimp farming is salinisation of surrounding agriculture and ground water Recent estimates of the total land area subject to direct salinisation impacts

as a result of inland shrimp farming is 22 455 ha, according to DOF, 1998 Much of this land was previously used for rice production and the possibility of returning to rice cultivation if shrimp production fails in these areas is very uncertain It is difficult to estimate the

production of shrimp from inland farming because the Department of Fisheries in Thailand does not identify if the shrimp originates from inland or from coastal farming However, it has been suggested that inland low salinity cultures account for 30-40% of Thailand’s production (Flaherty et al., 2000) Another source estimated that inland farming accounted for 40-50% of Thailand’s cultured shrimp production (Vandergees et al., 1999) According to the DOF, only 5% of the shrimp farms in Thailand are inland farms (Tookwinas, pers comm., 2001) These differences in estimations are mainly due to the large number of unregistered inland shrimp farms in Thailand today An association of inland shrimp farmers reported that inland shrimp farms have a total pond area of about 22 400 ha and would be able to produce approximately

100 000 tons of shrimp if the ban on inland shrimp farming is withdrawn (Asian Aquaculture Magazine, 2000)

6.7 Production process and water treatment

The production process involves four different stages: pond preparation, stocking, culturing and harvesting Pond preparation normally begins immediately after harvest and may take up

to a month After harvest the pond is cleaned of the wet mud using a tractor or a water jet Lime is used to sterilize the pond sediment and to reduce acidity in mangrove areas and other chemicals are used, for example, to reduce pests When the pond has dried out, seawater is pumped into the pond and the zoo- and phytoplankton multiply until they reach a sufficiently high concentration At the second stage the shrimp post-larvae are put into the pond

The culturing stage involves feeding, aeration, disease management and water management Feeding takes place 4 –5 times a day and the feed is mostly artificial Aeration is necessary in intensive shrimp farming to keep the oxygen levels high throughout the production The water currents created during aeration move uneaten feed and fecal material to the middle of the pond bottom In that way the feeding area along the sides of the pond is separated from the waste material For a 1 ha shrimp farm, seven aerators are commonly used (Patmasiriwat, 1998) If there are signs of disease symptoms the farmer normally treats the pond with

chemicals, but some farmers decrease the water exchange to almost zero out of fear for

disease and pollution

Water exchange is carried out to control water quality and to maintain the concentration of plankton at appropriate levels Maintenance of water quality is very important for the success

of shrimp farming Salinity, temperature, dissolved oxygen, pH, hydrogen sulphide,

biochemical oxygen demand (B.O.D), ammonia, nitrite, nitrate and chlorophyll levels have to

be optimized because of the high biomass content in the pond A number of practices can be used to improve the quality of the pond water These practices include the use of a

sedimentation pond and the use of a treatment pond (Thongrak et al., 1997)

A sedimentation pond is a reservoir used to settle out suspended sediments in the water before the water is pumped into the grow-out pond Presently, few farmers in Thailand use

sedimentation ponds since it requires converting a grow-out pond into a sedimentation pond, which reduces production Treatment ponds can be used in all the different intensive shrimp farming systems described above However, the practice is costly because it requires setting aside a pond for water treatment Throughout production, the water can be recirculated from the grow-out pond to a treatment pond and back again The recirculating system is a concept

in which the water from the shrimp pond is reused following various types of treatment processes This is done to ensure the quality and enhance the water utilization If the waste water is also recirculated at harvest there is a reduction of waste water discharge to the

• Biological treatment: By using filter feeding organisms such as mussels and oysters or nutrient-uptake organisms such as algae, seaweed and filter feeding fish (sea bass, mullet, tilapia etc.) the water will be cleaned

• Chemical treatment: Different chemicals and water treatment products are used that have different properties, for example liming materials, disinfectants and pesticides (The chemicals are described in greater detail in Chapter 6:10.)

Table 3 Potential natural treatment methods

Method Benefits

Mussel and oyster Removal of particulate organic matter and

phytoplankton from the water column Brackish water fish Removal of particulate organic matter

Red algae Removal of dissolved nutrients (nitrogen and

phosphorus)Sedimentation pond plus adding calcium

oxide and zeolite

Removal of particulate organic matter

Mangrove Used as a wetland to absorb nutrient and

increase the silting rate by mangrove trees

(Source: Tookwinas, 1995)

The fourth stage of the production process is harvesting, which is done about 120 – 140 days

after stocking The usual method is to cover the pond gate with a net and allow the water to

flow out of the pond This work is often carried out by professional harvesters

6.8 Diseases of cultured black tiger shrimp

In intensive shrimp farming systems there is a high risk of disease outbreaks, which are

caused by bacteria, virus, fungi or other pathogens The effect of a disease on a shrimp farm is

mostly seen as loss of production or loss of crop To prevent diseases it is recommended to

daily check the water quality and health of the shrimp Signs of illness include changes in

body colour and changes in activity (Patmasiriwat et al., 1998) The best ways to maintain

healthy shrimps are to use good quality post-larvae, to minimize stress, to have optimal water

quality, to avoid overfeeding and overcrowding in the shrimp pond and to use proper aeration

and pond preparations (ASCC News, 1996) If these conditions are not monitored, the

microflora, which is always present in the pond, can bloom at the expense of the shrimp

Today, immunostimulants such as betaglucans and glycans are tools for disease control in

shrimp These substances make the shrimps more resistant to viral, bacterial and other

infections (Primavera, 1998) Shrimp farming with closed systems has developed in a way to

reduce the risk for disease, while many bacterial and viral diseases can be transmitted through

water The most common shrimp diseases are Vibriosis, Yellow Head Disease and White Spot

Disease, which are described below

Bacterial diseases

Vibriosis caused by the bacteria Vibrio is a serious disease associated with poor husbandry

techniques in shrimp farming (ASCC News, 1996) In the grow-out pond, Vibriosis may

cause infections, usually one to two months after stocking Shrimp morbidity and mortalitity

may range from between 5% up to 80% in only a few days (Patmasiriwat et al., 1998) Poor

preparation of the pond bottom and pond water before stocking the shrimp might cause

Vibriosis by increasing benthic algal blooms on the pond bottom When the algae die the

number of pathogenic bacteria in the pond increase and the water quality deteriorates Weak,

unhealthy shrimp in poor water quality are more susceptible to pathogenic bacteria than

healthy shrimp Bacterial diseases are, though, treatable with antibiotics (ASCC News, 1996)

Viral diseases

The Yellow Head Disease is a viral disease that is caused by the yellow head virus The disease is activated by sudden changes in pH or by low dissolved oxygen levels in the pond (Kautsky et al., 2000) YHD is the most threatening disease of the shrimp diseases, although the pathogenicity of this virus appears to be decreasing

Another common viral disease is the White Spot Disease, which is caused by the SEMB virus (Patmasiriwat et al., 1998) This disease is the most recent of the Asian viruses The virus is extremely pathogenic and is considered responsible for severe production losses in Asia (Funge-Smith and Stewart, 1996) There are many other viruses such as Monodon Baculo Virus (MBV) and Hepatopancreatic Parvo Virus (HPV) that pose a threat to the shrimp The virus diseases mostly strike after periods of heavy rain when temperatures, salinities and water quality variables vary a lot (Rosenberry, 2001) It appears that White Spot Disease can

be introduced with post-larvae (Funge-Smith and Stewart, 1996) Thereby closed water systems may not be effective in reducing the risk for this disease

Viral diseases are not treatable although management techniques that lessen their impact have been developed A common practice is to harvest the shrimp in advance when they have viral diseases and sell them at the local market If the farmer waits too long before harvest the result will be high mortality and severe economic losses (Funge-Smith and Stewart, 1996)

6.9 Artificial shrimp feed

The use of artificial shrimp feed increases the profits and improves the production, although the feed is the largest component of production costs in intensive shrimp farming There are approximately 40 essential nutrients that are believed to be required by the shrimp Proteins and lipids are needed and are easily digested Fibres (carbohydrates) are not so easily digested and therefore increase the faecal production and pollute the water The commercial feed is enriched with vitamins but in high density ponds extra vitamins must be added to the feed to achieve normal growth The shrimp needs about 15 vitamins and there are also about 20 minerals in the feed Shrimp can absorb minerals directly from the aquatic environment via the gills and body surfaces Calcium is not needed in the feed because the brackish water usually contains high levels of this mineral Phosphorus, though, is usually limited in brackish water and is therefore needed in the feed (ASCC News, 1996)

A study of the composition of different brands of shrimp feed available in the south of

Thailand revealed no significant difference in gross composition (Funge-Smith and Stewart, 1996) About 60 – 70% of the Thai farmers buy their feed from the CP-company, who also export feed to other countries like Australia, Malaysia and Saudi Arabia According to theCP-company their shrimp feed contains 30% fish meal, 15% soya bean meal, 25% wheat flour, 8% fresh fish, 5% fish oil/squid oil, 5% cuttle fish meal, 5% shrimp head (dry) There

are also vitamins, minerals and probiotics in the feed The content of the remaining 7% of the feed is confidential (Kunjera, pers comm., 2001) There is a high demand for good quality fishmeal in Thailand since locally produced Thai fishmeal is of poor quality Fishmeal is therefore often imported from Central America and Norway and this practice keeps the price

of shrimp feed high

Most of the feed bags in Thailand are labeled with minimum protein, fat and with maximum fibre, minerals, calcium and phosphorus The date of manufacturing is also often indicated, because shrimp feed deteriorates quickly Shrimp feed should not be stored longer than three months from the time of processing even if stored in a cool and dry place (ASCC News, 1996)

6.10 Chemicals and biological products

Large amounts of chemicals are used in the shrimp farming industry today (Appendix 2) During 1995, almost 100 million US$ were spent on chemicals and drugs in Thailand

(Gräslund and Bengtsson, 2001) The most common products used in shrimp culture are liming materials and fertilizers To improve production, disinfectants, pesticides, antibiotics and probiotics are often used Some chemicals are used to control aquatic vegetation or to remove irritating organisms Other chemicals are used to disinfect pond water, to increase productivity or to increase the natural growth in the pond (Flaherty et al., 1999) Some of the chemicals are not functional at all Drugs and disinfectants may even have a negative effect

on the shrimp or on the pond environment Sometimes treatment is undertaken too late to have a beneficial effect

Free chlorinated residuals, such as hypochlorite, that are added to the natural water may react with organic substances and create chlorinated compounds Chloramines, that are produced when chlorine reacts with ammonia, and organochlorine compounds are less acutely toxic than free chlorine residuals The chlorinated hydrocarbons are probably formed after a

chlorination process of water, which contains organic matter The free residual chlorine and

combined residual chlorine has long been known to be toxic to several aquatic animals

(Gräslund, 1999)

Fertilizers

To increase the growth of natural food, fertilizers are widely used in the shrimp farming industry Normally, there is no need to fertilize the pond if commercial feed is added The organic group of fertilizers consists mostly of chicken manure The inorganic fertilizers are often mixes of ammonium phosphate and urea (Gräslund and Bengtsson, 2001)

Pesticides

To enhance agricultural production pesticides are used (insecticides, herbicides, fungicides, etc) to kill certain groups of unwanted organisms This is a serious threat to the shrimp culture industry itself because shrimps are among the most susceptible animals to pesticide toxicity both directly and indirectly Several pesticides are used in the shrimp industry, such as tea seed cake, which is widely used in Thailand to induce moulting in shrimps and to clean water before stocking Rotenone is another chemical that is used for removing unwanted fish from the pond water before stocking (Primavera et al., 1993; Gräslund and Bengtsson, 2001)

Probiotics

The hatchery-produced shrimp larvae can not reject diseases as well as wild-caught larvae The hatchery is a fairly sterile environment and therefore the hatchery-reared post-larvae have a low tolerance towards disease To reduce this risk of disease outbreaks, farmers use probiotics These are friendly microbes and are used to hold back and out-compete

post-pathogenic ones (Kautsky et al., 2000) According to Funge-Smith and Stewart (1996), the probiotics are widely used because of strong advertising campaigns by the companies and agents promoting them The products are said to improve the environment in the pond but the efficiency of the probiotics is not fully known They do not directly harm a shrimp pond since the bacteria are non-pathogenic, but they are a waste of money and may prevent the farmer from using other more efficient methods (Funge-Smith and Stewart, 1996)

Antibiotics

The widespread use of antibiotics to treat bacterial diseases in the shrimp culture industry has attracted a lot of concern Antibiotics should be used with caution to avoid unnecessary expense and increased bacterial resistance (Pednekar and Ochieng, unpublished) Antibiotics are commonly used in intensive shrimp farming, both in the hatcheries and in the grow-out ponds Many farmers use antibiotics not only when the shrimp show signs of disease but also prophylactically to prevent outbreaks of disease (Flaherty et al., 1999) It is, for example, common to use antibiotics in the last week of the first month after stocking to prevent the one-month disease The antibiotics are either added in the pond water or mixed with the shrimp feed (Primavera et al., 1993)

Antibiotic usage is common in shrimp farming in Thailand and the most common drug is oxytetracyclin, which is also known as the cheapest on the market Norfloxacin, oxolinic acid and chloramfenicol are other common antibiotics in the shrimp farming industry (Funge-Smith and Stewart, 1996)

Corticosteroids, anabolic steroids and steroid hormones have been identified in some shrimp diets These substances are sometimes added to shrimp hatcheries to give the larval shrimp a uniform size and a good appearance When these post-larvae are transferred to nursery and grow-out ponds, they are very sensitive to external stress and pathogens and growth

retardation and mass death may occur The drugs apparently damage the immune system of the shrimp These drugs in shrimp feed may have had a great contribution to the Taiwanese collapse of the shrimp industry (ASCC News, 1996)

7 Description of the alternatives

7.1 Zero alternative: Semi-closed intensive system

If the situation does not change, a semi-closed intensive shrimp farming system will still be the most common used method in Thailand in the future (Figure 4) The size of an average semi-closed farm is about 2 ha

In this alternative the water is treated in the grow-out pond before stocking with, for example, lime, dolomite and zeolite There is no water exchange in the pond during the first two

months Thereafter, 5% of the water is exchanged every week No treatment pond exists Fertilizers, bacteria and plankton are added to the pond during culture Antibiotics are used when the shrimp are stressed and show signs of disease, but also prophylactically the last week of the first month Chemicals like chlorine, iodine, tea seed cake, hydrogen peroxide, malachite green, formaline and potassium permanganate are used before stocking or during the grow-out period The farmer feeds the shrimp with pellets about five times a day and vitamins are also added

Paddles are used to oxygenize the pond Typical daily fuel consumption for diesel aeration in southern Thailand is between four and twelve litres per rai and day according to Funge-Smith and Stewart (1996) The paddles are operating all day except at the time of feeding

The accumulated sludge at the bottom of the pond is removed mechanically with heavy

machinery after harvest Special dumping sites exist in some areas of Thailand but mostly the sludge is removed after each crop and is put in a pile next to the pond or is used to build dikes (Funge-Smith and Stewart, 1996) Semi-closed intensive shrimp farms have a maximum life

of 10 years in Thailand (Gujja and Finger-Stich, 1996) According to a survey performed by Funge-Smith and Stewart (1996) the average life of shrimp farms in southern Thailand is

2 – 5 years

Since the semi-closed intensive farms operating in Thailand today are situated both

close to the mangrove forest and in non-mangrove coastal areas, the zero-alternative is

divided into two examples In the southeastern parts of Thailand most of the farms are located

in non-mangrove areas This means that the zero-alternative A is the most common example

Zero-alternative A

In this variation of the zero-alternative the shrimp farm is located in a coastal area far away from the mangrove forest The intake water is transported to the farm through pipes from a common water canal Many farms in one area use the same water resource because of the high costs of transporting water through pipes directly from the sea Consequently, the waste water from one farm becomes the intake water of the neighbouring farm A typical example of an area with this kind of shrimp farm is Ranod in the province of Songkhla (Figure 1)

Zero-alternative B

In this example of the zero-alternative the shrimp farm is situated behind the flooded

mangrove fringe, that is in the secondary forest or on mudflats The seawater is transported through pipes directly to the grow-out pond An example of an area with this kind of shrimp farms is Nakhorn Sri Thammarat

Figure 4 Semi-intensive shrimp farming (zero-alternative)

7.2 Alternative 1: Closed recirculating system

In this alternative a closed recirculating, intensive shrimp farming system is used (Figure 5) The farm is not located in a mangrove forest area and consists of several ponds The initial incoming sea water is transferred through a settlement pond before reaching the grow-out ponds The intake water is prepared with the use of tea seed cake and agricultural lime like calcium bicarbonate and dolomite If needed, fertilizers are added to accelerate the growth of phytoplankton in the pond

Four sets of paddle wheel aerators (8 hp per pond), each with four wheels, are used to move the sediment in the pond towards the middle and to aerate the water The paddles are working about 10 hours a day and electric energy is used instead of diesel Bottom aeration, with submerged air diffusion tubes (one tube about every ten meters), is used to enhance the

vertical circulation and thereby bring oxygen to the bottom of the pond The aeration tubes are connected to an electric motor (1 hp per pond) and are used about 20 hours a day In this way

a lot of energy is saved

Normally about 3-5% of the water in the grow-out pond is transported to a treatment pond every day This occurs twice the first month, three times the second month and five to eight times during the third and fourth months In cases of poor water quality, a continuous

circulation is carried out until the water quality has improved In the treatment pond the water

is cleaned by the use of seaweed, plankton and different fish (for example Tilapia and Dwarf goby) A biological sand filter with oyster shells is also used The farmer feeds the shrimp with pellets about five times a day and vitamins are also added

At harvest the waste water is not discharged into the surrounding water bodies, it is

transported to a waste water treatment pond In this pond, fish, molluscs, seaweed and a sand filter are used to treat the water After treatment, the water is recirculated to the grow-out pond and is used again After the water is drained from the grow-out pond the pond rests for two months, which enables the sludge to decompose by natural microbal activity Some water

is added in order to maintain moisture and to increase the microbal activity This means that

no sludge needs to be disposed of at all (Songsangjinda, pers comm., 2001; Tookwinas, 2000)

Figure 5 Closed recirculating system (alternative 1), with air diffusion tubes

7.3 Alternative 2: Sludge removal system

In this alternative, a sludge removal system is used and the farm is not located in a mangrove area (Figure 6) The intake water is taken from the sea and is treated with lime Aeration paddles driven by electricity oxygenize the water Normally, 16 paddles, operating 24 hours a day, per 1000 sq.m pond surface are used There is no water exchange during the grow-out period No antibiotics or chemicals are used during the production period on a regular basis Formaldehyde is sometimes used to kill plankton Fertilizers, bacteria and plankton are added

to the pond during culture The farmer feeds the shrimp with pellets about five times a day and vitamins are also added

At harvest, the water is drained into the surrounding environment without any treatment In this alternative the sludge is removed from the ponds during the whole growth period This is carried out by a moving chain, which is dragged along the bottom of the pond and thereby suspends the sludge The sludge is pumped through a trickle filter, which needs ammonia to feed the microorganisms on the filter Four grow-out ponds at different production stages use the same trickle-filter, in this way no extra ammonia needs to be added to the filter By removing the sludge during production, the nitrogen outlet is decreased by 70% and the phosphorus by 90% The remaining 30% and 10%, respectively, are due to the waste water outlet at harvest The sludge is transported to a concrete tank and could in the future be stabilized and used in the ponds to protect the walls against erosion (Andersen, pers comm., 2001; Andersen, 2000)

Figure 6 Sludge removal system (alternative 2), with trickle filter treatment

8 Environmental impacts

8.1 Mangrove deforestation

Mangrove forests are highly productive and are vital for healthy coastal ecosystems The destruction of the mangrove forest in order to construct shrimp farms results both in a loss of the important mangrove ecosystem and the mangrove-related ecosystems of mudflats, sea grass beds and coral reefs, which the mangroves support

The forest detritus, consisting mainly of fallen leaves and branches from the mangroves, provides nutrients for the marine environment and supports immense varieties of sea life in complex food webs Many fish, crabs, shrimp, and molluscs use mangroves as nursery

grounds and shelter during their juvenile stages The loss of the mangroves has severe

consequences for the marine environment

Mangroves are crucial nesting and migratory sites for many bird species Thousands of shore birds roam on mud flats and mangrove forests in the Gulf of Thailand on their way from the Arctic circle to Australia and New Zealand Shrimp farms and salt farms also provide suitable habitats for birds such as egrets or stilts The abandoned shrimp farming areas of the Inner Gulf of Thailand are providing a paradise for shore birds Because its importance as a resting place, the Inner Gulf of Thailand was designated an important bird area by the Bird

Conservation Society of Thailand The Gulf is also recognised internationally for its

importance in providing a habitat for endangered birds Altogether, the Inner Gulf provides a home to some 67 species of water birds (Wetlands International) Manatees, crab-eating monkeys, fishing cats, monitor lizards and sea turtles also make use of the mangrove

wetlands Seagrass beds provide food for some sea-turtles and dugongs, both of which are near extinction in Thailand

Suspended materials are filtered by the forest, which also assimilates dissolved nutrients, thereby recycling nutrients and reducing pollution by trapping heavy metals and pesticides In addition to the filtration of nutrients and pollutants, the water quality is maintained by

neutralization of potential sulfuric acids by frequent flooding and by maintenance of

groundwater levels and prevention of salt water intrusion Vital coral reefs and sea grass beds are also protected from damaging siltation in this way Ideally, shrimp farms should be

situated behind the mangrove areas and discharge effluents through the mangrove system The roots protect the coastlines from erosion, storm damage and heavy winds by stabilizing the sediments Erosion rates on coast lines where the mangroves have been removed can be as much as 20 times greater than along undisturbed mangrove coast line (Platong, 1998) Also the coastal areas behind the mangrove fringe forest are protected from wave damage and erosion

The destruction of the mangrove forest decreases the possibility for carbon dioxide to be assimilated This may increase the greenhouse effect because carbon dioxide is a greenhouse gas If the mangroves are removed, the biodiversity is negatively affected The mangrove forest has a high conservation value because of this

Zero alternative

At the present time, construction of shrimp farms is banned in mangrove forests in Thailand Many farms are still situated in mangrove areas and some illegal farms are constructed despite

of the ban In zero-alternative B, where the pond is located in the secondary mangrove forest, some of the impacts above are valid Since the secondary mangrove forest is not flooded continually there will be a limited amount of marine animals like crustaceans and molluscs in this area Other animals like monkeys and sea turtles will, though, be affected if this

secondary mangrove forest is cut down If the shrimp pond is constructed on a mud flat, many bird species will be impacted Since, in this case, only the secondary forest is cut down, there will still be some flooded mangrove left that can filtrate the water in the area and trap

nutrients and chemicals This flooded forest will protect the coast from erosion, although the ability will be decreased when the secondary forest disappears

Zero alternative

The semi-closed shrimp farms in Thailand that are situated in the secondary mangrove

(zero-alternative B) can impact the forest negatively through changes in the hydrology of the area Despite the limited size of the farming area these farms can create barriers for the

spreading of mangrove fauna and flora, especially if many farms are situated close together

In most shrimp farming areas, the ponds are very densely located along the coast, which causes huge physical barriers In zero-alternative A, where the shrimp farm is situated in a non-mangrove area, the negative impact is mainly that the densely located farms can create barriers for animals that wish to reach the sea

Alternative 1

In this alternative, a large farming area is needed for the construction of treatment ponds and recirculating canals This suggests that the farm area can change and restrict natural water movements The large farm area can also create a significant barrier for the spreading of wild flora and fauna Together with many other shrimp farms in the same area, the farm creates a considerable barrier

Alternative 2

According to the second alternative, the farming area is also quite big since four ponds are placed closely together This will give rise to physical barriers for the spread of wild flora and fauna but also changes in natural water movements If the farm is situated in an area with a large number of shrimp farms, the effect of the barrier is even more significant

8.3 Pollution by chemicals and water treatment products

Chemicals may enter the environment directly or pass through the body unabsorbed and be excreted in the faeces (Primavera, 1993) Many of the chemicals used in the shrimp farming industry may pose a risk not only to the unwanted target species but also to the local flora and fauna and even to the cultured shrimp itself Their potential effect on non-target organisms depends on toxicity, amount, degradation rate, dilution and distribution (Pednekar and

Ochieng, unpublished) The chemicals may be acute toxic, mutagenic or cause other lethal effects on the local flora and fauna (Gräslund and Bengtsson, 2001) The toxic waste water from the shrimp ponds pollutes the mangrove forest, which gives rise to the same negative impacts as described above In areas densely covered with intensive shrimp farms, considerable impacts on the environment can occur Waste water from shrimp farming

sub-together with urban, industrial, agricultural and other aquacultural chemical pollution gives rise to vast negative impacts on the environment

The widespread use of antibiotics in shrimp farms and hatcheries might cause resistance among pathogens and cause changes in the composition of microorganisms in the aquatic environment (Gräslund and Bengtsson, 2001) Antibiotic use reduces natural microbial

activity, which leads to waste accumulation and reduced degradation and nutrient recycling The entire ecological structure of the benthic microbial communities may be influenced (Rönnbäck, 2001)

The impact on the soil is related to the water quality When waste water reaches the

surroundings, soil conditions such as pH, salinity and oxygen content are changed Another important issue is the persistence of chemicals Chemicals such as organophosphates, copper compounds and other compounds that have high affinity to sediment are used in the shrimp farming industry These chemicals produce persistent, toxic residues that have an expected negative impact on the environment These persistant antibiotic and chemical residues can remain for a long time in sludge piles that are not sun-dried properly (Funge-Smith, pers comm., 2001) A substantial persistence of a chemical or by-product may change organisms living in contact with the ponds and organisms in other ecosystems through bioaccumulation, biomagnification or physical transport through air, water or soil (Gräslund and Bengtsson, 2001)

Zero alternative

Waste water from the shrimp ponds is discharged or leaches out into the natural waterways, the surrounding soil or along the coast without any treatment The present method of intensive shrimp farming is heavily dependent on use of chemicals and drugs during the grow-out period because of frequent problems with poor water quality and disease (Appendix 2) Today there is a lack of information about the quantities of chemicals being used in the shrimp farming industry in Thailand, which leads to difficulties in estimating the potential impact of chemicals on the environment Since the Thai shrimp farms are often situated very close to each other and the water sources often are shared, the risk for widespread pollution by

cumulative effects is very high Since large amounts of antibiotics are used in the

zero-alternative, resistance among pathogens and changes in the composition of

microorganisms may occur

If the farm is not located in a mangrove area (zero-alternative A) the chemicals still pose a threat to the local flora and fauna and also to the marine environment In zero-alternative B, where the farm is situated in the secondary mangrove forest, there is a high risk that the

sensitive local flora and fauna is negatively impacted by the pollution Chemicals can build up

in the mangrove soil and bioaccumulation in animal tissue can easily occur On the other hand, the negative effects of pollution on the marine flora and fauna further away from the pond is reduced since the forest traps heavy metals and pesticides

Alternative 1

Since the only chemicals used are tea seed cake and antibiotics, the waste water does not contain large amounts of chemicals There is, though, a limited risk for antibiotic resistance and changes in the composition of microorganisms Liming materials like dolomite and calcium bicarbonate are used, which can impact the environment if used in high amounts The system is recirculating, therefore no waste water will be discharged into the nearby water bodies, other than at seepage This minimizes the negative impacts

Alternative 2

In this case, only formaldehyde and lime are used and therefore there are only small amounts

of chemicals in the waste water The waste water is only released into the environment at harvest No problems with antibiotic resistance will occur since no antibiotics at all are used

8.4 Sedimentation

In 1994, approximately 16 million metric tons of dry sediment were produced from the

40 000 ha of intensive ponds in operation in Thailand that year Between 139 and 150 m3 of sediments per ha are accumulated at the bottom of an intensive shrimp pond This pond

sediment is unusable as an agricultural fertilizer because of its high salt content, low organic content and its potential chemical and antibiotic content (Dierberg and Kiattisimkul, 1996)

According to Funge-Smith and Briggs (1998), erosion of the pond soil is the major source of solids (88-93%) in intensive shrimp farms The erosion is mainly due to water currents

induced by the aeration paddles The eroded material is either suspended and discharged with the waste water or is removed as sludge from the bottom of the pond Particles transported with the discharge water will not decompose and may cause turbidity of water courses,

shoaling of offshore waters and siltation of canals and river mouths The mangrove forest is negatively impacted by the sedimentation, since the roots get choked Coral reefs and sea grass beds are also affected by the sedimentation

Zero alternative

The massive aeration of the ponds in intensive shrimp farming causes large amounts of solids

to erode from the pond walls and be transported to the sludge on the bottom of the pond The practice of discarding the sludge directly into waterways, using water jets, is banned in

Thailand In fact, the effect if the sludge is put on a pile is actually identical to the effect if the sludge is flushed into the waterways, while rainfall easily can transport the sludge into the canals

In zero-alternative A, where the farms are not in a mangrove area the major impact is that canals are clogged and dried out because of siltation When, on the other hand, the farm is located in or near the mangrove as in zero-alternative B, the sludge that ends up in the

surrounding environment will impact the mangrove negatively by sedimentation and thereby also the sea grass beds and the coral reefs As the mangrove forests are considered common property, many shrimp farms that are situated in or near the mangrove illegally dispose the

sludge from the pond cleaning directly into the forest and this causes damage and death to the flora and fauna

Alternative 1

Since there is no external water exchange during the whole production phase, no sludge is let out into the surrounding environment At harvest the waste water is recirculated to a treatment pond The sludge from the pond bottom is not removed but is left to decompose In this way

no problems of sedimentation due to sludge discharge will occur Since only a few aeration paddles are used there will only be a limited erosion from the pond walls and a relatively small amount of solids will be transported to the bottom sludge

Alternative 2

In this system the sludge is removed and cleaned every day The removed sludge is put inside

a concrete pond where no leakage can occur, but this is only a temporary solution There are plans to reuse the sludge in the shrimp pond The idea is to build bricks of the sludge and place them on the pond wall to prevent the sides from erosion In the meantime, the sludge is put in concrete ponds

In this alternative, the aeration of the pond will be similar to the zero alternatives and a large amount of solids will be transported to the pond bottom At harvest, the water is drained into the waterways, but at this point the water does not contain much solids since it is cleaned every day

8.5 Salinisation and the extraction of groundwater

Shrimp farming in non-mangrove coastal areas, agricultural areas and in freshwater wetlands cause surface and subsurface saltwater intrusion into the surrounding environment This is generated by the discharge of wastewater into canals and by saltwater leakage or overflow from the earthen shrimp ponds and leakage from sludge piles during rainfalls In the south of Thailand, the most obvious impact from the leaking of brackish water to the surroundings is the loss of sugar palm trees that once grew on the rice fields (Figure 7)

To compensate for evaporation and reduced salinity, groundwater is often extracted from freshwater aquifers This lowers the water table and causes sea water to flow inland into freshwater sources (Funge-Smith and Stewart, 1996) In Ranod province, the groundwater level sank four meters in two years, from 1989 to 1991 Today, sinking water tables due to high densities of shrimp farms in, for example, Taiwan have even been reported to cause sinking land levels (Barraclough and Finger-Stich, 1996)

Figure 7 A common sight in shrimp farming

areas, polluted canals and dead sugar palms The

sugar palms can not cope with saline water

intrusion from adjacent shrimp ponds

Zero alternative

In the semi-closed system there is a limited water exchange after the first month and therefore salinisation of the surrounding environment is a problem A certain leakage from the earthen ponds also occurs as well as a significant salinisation due to rainfall on the sludge piles Groundwater is sometimes extracted or fresh water is taken from nearby waters

A shrimp farm that is situated in a non-mangrove area (zero-alternative A) will bring about problems with salinisation while a farm in a mangrove area (zero-alternative B) will not cause any particular problems, because of the already saline soil Since the farm is located in the fringe of the mangrove forest there is, though, a possibility that adjacent agricultural activities may become negatively impacted

Alternative 1

In the closed farming system there is no salinisation problem due to water exchange

Salinisation may, though, occur through seepage Since the water is recirculated and is not exchanged it will be very salty due to evaporation, therefore fresh water has to be added on a regular basis No ground water is extracted

Alternative 2

In this alternative there is no salinisation problem due to water exchange except at harvest Salinisation may, however, occur through seepage Since the water is not exchanged there will be a build-up of salt due to evaporation Therefore fresh water has to be added on a regular basis No ground water is extracted