shellfish aquaculture in thailand

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Shellfish aquaculture in ThailandK. Chalermwat a , B.W. Szuster b & M. Flaherty ca Department of Aquatic Science , Burapha University , Bang Saen, Chonburi, 20131,Thailand Phone: +66 38 745900 x 3092 Fax: +66 38 745900 x 3092 E-mail:b Thailand Aquaculture Management Project , Burapha University , Thailandc Department of Geography , University of Victoria , CanadaPublished online: 13 Nov 2008.

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COUNTRY REVIEW

Shellfish aquaculture in Thailand

K. CHALERMWAT1, B.W. SZUSTER2 AND M. FLAHERTY3

1 Department of Aquatic Science, Burapha University, Thailand2 Thailand Aquaculture Management Project, Burapha University, Thailand3 Department of Geography, University of Victoria, Canada

Abstract

Shellfish have been farmed in Thailand for over 100 years, and during this time, traditionalculture techniques have gradually given way to more sophisticated and capital intensivemethods. Farmed shellfish production increased from 73,976 to 138,202 metric tonnesbetween 1988 and 2000. Major species currently under cultivation include the green musselPerna viridis, the blood cockle Anadara granosa, and three species of oyster (Saccostreacucullata, Crassostrea belcheri, and Crassostrea iredalei). The horse mussel Arcuatulaarcuatula is also produced in limited amounts for animal feed, and gastropods such as theabalone Haliotis asinina and the spotted babylon Babylonia areolata are in the initial phasesof commercialization. With the globalization of fisheries commodity markets, the Thaishellfish sector is slowly implementing more rigorous management and certificationprocesses. These procedures are required to access European, American and Japanesemarkets, and would also serve to decrease the risk of gastrointestinal disease for localconsumers.

Key words: Thailand, shellfish, aquaculture

Introduction

Shellfish have long been an important source of food for the Thai people who consumeapproximately 3.42 kg of these products each year on a per capita basis (FAO 2002). Thecommercial shellfish sector in Thailand can be divided into three main categories: speciesobtained from a wild harvest on natural grounds; species produced through traditionalaquaculture techniques without associated hatcheries; and species whose cultivation is whollydependent upon hatchery technology. The first category includes a variety of bivalves withthe largest existing fishery focusing on the harvest of the short-necked clam Paphia undulata.Smaller fisheries also exists for scallops such as Amusium pleitronectes and the razor clamSolen strictus. Traditional aquaculture techniques such as bamboo stake culture wereimported by Chinese immigrants, and cultivation methods evolved in conjunction with theheavy exploitation of natural stocks. Bivalves currently farmed in Thailand using traditionaltechniques include: the green mussel Perna viridis, the blood cockle Anadara granosa, thehorse mussel Arcuatula arcuatula, and three species of oyster. Saccostrea cucullata ("smallrock oyster") is primarily grown in the Upper Gulf and eastern regions of Thailand, while

Correspondence Dr Kashane Chalermwat, Department of Aquatic Science, Burapha University,Bang Saen, Chonburi 20131 Thailand. Tel: +66 38 745900 x 3092. Fax: +66 38 393491. Email:[email protected].

Aquaculture Economics & Management 7(3/4) 2003 249

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250 Shellfish aquaculture in Thailand • K. Chalermwat et al.

Crassostrea belcheri and Crassostrea iredalei ("big oysters") are generally raised in southernThailand. The final category of commercial shellfish production is wholly dependent onhatchery technology and harvests are very small compared with the wild harvest andtraditional aquaculture categories. Species currently produced with hatchery technologyinclude the abalone Hàliotis asinina (Jarayabhand and Paphavasit 1996) and the spottedbabylon Babylonia areolata (Chaitanawisuti and Kritsanapuntu 1997a, 1997b, 1998).

Major cultivated species

Molluscan shellfish farming is practiced in every coastal province of Thailand (Figure 1).Aquaculture has emerged as an increasingly important component of overall shellfishproduction as wild harvests declined dramatically during the late 1980s and early 1990s(Figure 2). Natural shellfish harvests have deteriorated as a result of over-exploitation, andover 70% of all shellfish produced in Thailand each year are now derived from aquaculture.Recent increases in farmed harvests has even allowed total annual shellfish production torebound in spite of substantial declines in the wild fishery.

vr

AndamanSea =0 0-VA

\ Malaysia ^ ' j , /

Figure 1 Coastal Provinces of Thailand

Aquaculture Economics & Management 7(3/4) 2003,

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K. Chalermwat et al» Shellfish aquaculture in Thailand 251

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Figure 2 Total Shellfish Production in Thailand (1988-2000)

Source: Department of Fisheries 2000 and FAO 2002

Although traditional aquaculture methods are still very prevalent, the quantity and value offarmed shellfish in Thailand have increased through the introduction of culture systems suchas oyster rafts and mussel long-lines. Unfavorable environmental conditions (e.g., extremesalinity changes during the growing season) have reduced fanned shellfish production in keygrowing regions during individual years, but these events have been exceptions in an overallpattern of steady growth. Total farmed shellfish production was 138,202 tonnes in 2000,which was valued at approximately $47 million USD1. Green mussels and blood cocklesrepresent over 80% of the total cultured shellfish harvest by weight, but the relatively smalloyster harvest is much more valuable and provides almost 50% of the total annual farmedshellfish crop value (Figures 3 and 4).

Figure 3 Distribution of Thai Cultured Shellfish Harvest - Tonnage (2000)

Sources: Fisheries 2000 and FAO 2002

1 Thailand's exchange rate was fixed at 25 baht to the US dollar between 1988 and 1997. The baht was floatedin 1997 and decreased to approximately 40 baht to the US dollar in 1998. This later exchange rate was usedto calculate production values in 1998-2000.

Aquaculture Economics & Management 7ß/4) 2003

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Figure 4 Distribution of Thai Cultured Shellfish Harvest - Value (2000)

Sources: Department of Fisheries 2000 and FAO 2002

Green MusselsThailand is a major producer of the green mussel Perna viridis which is generally marketedfresh and consumed in the domestic market Aquaculture provided the entire green musselharvest of 61,202 tonnes in 2000 (FAO 2002; Department of Fisheries 2000) and this cropwas worth approximately $5 million USD (Figure 5). Over 90% of the total annual greenmussel crop was raised in Upper Gulf of Thailand provinces such as Phetchaburi, SamutSongkhram, Chonburi and Chachoengsao (Table 1). Green mussel harvests have been fairlystable and typically within the range of 50,00 to 70,000 tonnes per year during the 1988-2000period. An exception to this was 1992 when harvests were affected by poor water qualityconditions in the Upper Gulf of Thailand.

90,000

80,000

70,000

60,000

g, 50,000

g 40,000

° 30,000

20,000

10,000

0

/ — \

' \..--A if-

é

• \

"'•• A-J x

— Quantity- - Value

$12,000,000

$10,000,000

$8,000,000

$6,000,000

$4,000,000

$2,000,000

$0

DCO

o

I

CD

8

Year

Figures Green Mussel Production in Thailand (1988-2000)


Green mussels were initially raised as a secondary opportunistic crop that formed on bamboopoles used to construct off-shore fish traps in the Gulf of Thailand (Chalermwat and Lutz1989). Bamboo pole and palm stake substrates were subsequently introduced in coastal

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K. Chalermwat et cd» Shellfish aquaculture in Thailand 253

regions during the late 1950's as Thai aquaculturalists began to view green mussels as afeasible primary crop. The bamboo poles are typically 6-8 meters in length (depending onwater depth) and are staked into the sea floor approximately 1 meter apart. In shallower waterareas such as Chachoengsao, farms tends to be smaller and use 2000-8000 poles per farm. Indeeper water areas such as Phetchaburi, farms are larger and can use up to 250,000 poles(ibid.). Palm stake are used in shallower areas. Very little additional attention is needed afterthe poles or stakes are set by farmers as this system depends completely on abundant naturalspatfalls. Harvesting usually takes place after six months when the mussels have reached asize of 60-70 mm (Vakily 1989). Harvesting the mussel masses is performed using dip nets ifthe poles are left in-situ, or a sharpened iron bar if the poles are removed and hauled into aboat. The harvesting of green mussels from fish traps continues, but this represents anincreasingly smaller proportion of over-all harvests because fewer of these structures areconstructed in the Gulf of Thailand each year. Only 5,200 tonnes of green mussels wereharvested from fish traps in 2000 which represented 8.5% of the overall farmed green musselproduction during that year.

Table 1 Shellfish Production by Zone and Province (1998)

PROVINCE

Coastal Zone 1TratChantaburiRayong

Coastal Zone 2ChonBuriChachoengsaoSamut PrakhanSamut SakhonSamut SongkhramPhetchaburi

Coastal Zone 3Prachuab Kriri KhanChumphonSuratThani

Coastal Zone 4Nakhon Si ThammaratSongkhlaPattanlNarathiwat

Coastal Zone 5RanongPhangngaPhuketKrabiTrangSatun

COCKLEQuantity

431

431-

7,011-

9156,096

19,981

-19,981

1,313750

-563

-

15,414-

11,193

4,221

Value$167,025

.$167,025

-

$2,247,925-

$343,075$1,904,850

$6,583,125

$6,583,125

$316,700$150,000

$166,700-

$3,572,675

$2,238.550•

-

$1,334,125

GREEN MUSSELQuantity

168168

-

52,16710,50712,1673,683

.5,223

20,587

4,410

4,410-

0

--

197197

Value$14,700$14,700

•

-

$5,236,400$619,250$912,450$433,825

•

$432,550$2,838,325

$330,775

$330,775-

$0

$65$65

125125

--

OYSTERQuantity

713482231

-

10,01110,011

-

-

7,8471020

7,817

1---1

3,89663

3,833.•

-

-

Value536,35074,675461,675

-

6,058,0256,058,025

-•

-

-

9,861,300218003,950

9,835,550

1,150•

-

-

1150

4,260,825147,575

4,113,250----

Source: Department of Fisheries 2000

Non-traditional culture systems that utilize rafts and long lines have also been adopted forgreen mussel production in Thailand. Raft culture was introduced in the late 1980's and isnow practiced in several major mussel growing regions (Chaitanawisuti and Menasveta1987). Long line techniques were recently developed by the Department of Fisheries and theKasetsart University Research Station in Chonburi province, and this technology appears tohave significant potential to further increase mussel production. Water quality conditions in


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the Upper Gulf of Thailand are of concern, however, because this important production areareceives runoff from four major rivers that drain a majority of the Thai landmass. Asubstantial amount of industrial and municipal effluent is entrained within this runoff, andmussels grown in the Upper Gulf of Thailand are susceptible to contamination from heavymetals, fecal coliforms, and toxic dinoflagellates. Deteriorating environmental conditionsrepresent a serious constraint to mussel production, and little potential exists for thedevelopment of export markets unless water quality conditions improve markedly.

OystersThe Thai oyster farming industry has achieved major advances in recent years and is now thesingle most valuable component of the entire farmed shellfish sector. All Thai oysters areproduced by aquaculture and annual production reached 22,000 tonnes in 2000 (Figure 6).Although this represents only approximately 16% of the total farmed shellfish output, thevalue of this crop is significant and worth more than $22 million USD. Oyster production hasincreased steadily over the past decade with the exception of 1997 when mass mortalitiesoccurred in Surat Thani as a result of unusually low water salinity. Three species of oystersare raised in Thailand. The small rock oyster Saccostrea cucullaia is largely produced inChonburi province and is a popular food item for people in the Bangkok region. The "smalloyster" is typically sold as shucked meat in local markets, bottled in brine, or frozen for salein more distant locations (Tiensongrasmee 2000). Crassostrea belcheri and Crassostreairedaleii are larger sized oysters that are primarily raised in the southern Thai provinces ofSurat Thani and Phangnga (Table 1). Attempts have been made to raise big oysters in easternThailand, but these efforts have achieved only limited success. Crassostrea belcheri andCrassostrea iredalei are typically sold fresh and "shell-on" to local restaurants, shucked forsale in local markets, or preserved by smoking or brining. The "big oyster" of Surat Thanicurrently represents the only significant shellfish product exported by Thailand to markets inSingapore and Hong Kong.

$40,000,000

$35,000,000

$30,000,000

$25,000,000

$20,000,000

$15,000,000

$10,000,000

$5,000,000

$0

Figure 6 Oyster Production in Thailand (1988-2000)


Grow-out techniques have evolved substantially since Saccostrea cucullata was firstcultivated commercially in eastern Thailand in 1942 (Brohmanonda et al. 1988). Traditionaloyster culture methods involved placing rocks on hard or sandy substrates to promote natural

ato

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K. Chalermwat el al» Shellfish aquaculture in Thailand 255

spat settlement. Semi-traditional techniques utilize bamboo poles or cement objects such aspoles, blocks, or pipes driven into the seabed. These concrete objects can be used as spatcollectors, or oyster seed can be obtained using other materials such as bamboo poles orcement disks and transferred to the grow-out medium. Semi-traditional techniques continueto be used throughout Thailand's main oyster production areas and require 1.5-2 years foroysters to reach a marketable size. Modern grow-out techniques focus on the use of hangingculture or trays. With regard to Saccostrea cucullata, oyster spat collected in Chantaburi andRayong provinces are transported to grow-out sites along the Eastern Seaboard. The oysterspat are then transferred to lines and hung on bamboo racks or rafts in deeper water protectedfrom winds and high waves. A similar process is followed in southern Thailand for theculture of big oysters, but spat is collected in Songkhla province (Crassostrea iredcdeî) andPrachuap Khiri Khan province (Crassostrea belcheri). Hanging culture techniques havesignificantly increased the productivity of oyster production in Thailand, and in some areassuch as Chonburi province, have largely replaced semi-traditional culture methods. Althoughthe Thai oyster industry has progressed rapidly in recent years, future growth is constrainedby a lack of hatchery support to ensure a consistant supply of seed stock. All farmed oystersare obtained from natural sets and the lack of hatchery-raised oyster spat leaves the industrysusceptible to variations in the natural environment that can severely reduce both seedsupplies and harvests.

Blood CocklesThe production of the blood cockle Anadara granosa has become an increasingly importantcomponent of the overall farmed shellfish sector in Thailand. The entire Thai cockle harvestis supplied by aquaculture and production has increased substantially in recent years to55,000 tonnes (Figure 7). Value of the cockle harvest in the year 2000 was approximately$20 million USD. Cockles are exclusively produced for the domestic Thai consumer wherethey are sold fresh in markets throughout the country. Traditional production areas includethe Upper Gulf of Thailand region and the southern Andaman coast, but the emergence ofSurat Thani as a major new cockle farming area has greatly increased total annual harvests inrecent years (Table 1).

QCO

S

YearFigure 7 Blood Cockle Production in Thailand (1988-2000)



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Blood cockles are a shallow water species found in abundance on tidal flats within coastaland estuarine areas. Cockles prefer a fine muddy substrate that allows them to create shallowburrows for protection. Existing traditional forms of cockle farming have been practiced inThailand since the early 1900s when semi-culture practices were introduced to Petchaburiregion (Tookwinas 1985). Early farms operated by collecting natural spat from local growingareas and transporting this seed to penned mudflats where it was re-sown and raised to amarketable size. Cockle pens are made of small bamboo slats approximately 50 cm in heightand typically cover an area of 1-2 hectares. Harvesting occurs after 1-2 years when thecockles reach a diameter of 4 cm (or 25 gm) and is performed manually using a self-propelledmud-ski or a metal cockle rake. Traditional forms of semi-culture continued relativelyunchanged into the early 1970s when a deterioration of natural cockle sets forced Thaiproducers to import seed from Malaysia. At present, cockles are primarily cultivated insouthern Thailand as a result of poor water quality conditions in the Upper Gulf of Thailand.Traditional culture practices remain the norm and seed continues to be imported fromMalaysia. Natural cockle sets have increased in some areas, however, and this has allowedfor some additional expansion. The most important existing cockle production areas includeSurat Thani, Phangnga, Satun, and Phetchaburi provinces.

Other Cultivated SpeciesThe striped horse mussel Arcuatula arcuatula is a small species primarily utilized as animalfeed in Thailand as opposed to human consumption. Production of this species has declinedto very low levels in recent years, but these molluscs are still a preferred source of feed fortiger prawn {Penaeus monodori) broodstock rearing operations. Striped horse mussels aretypically gathered from natural growing areas when they are about 0.5 cm long, andredistributed within plots that are located in shallow, muddy areas close to shore (Lutz et al.1991). The horse mussels are retained in the plots for 2 to 3 months until they reach a size of3 to 4 cm in length and are then harvested.

The cultivation of gastropods in Thailand has only recently been promoted, and initialefforts began with the development of hatchery techniques for the tropical abalone Haliotisasinina in the late 1990s. This small abalone (maximum shell length of 10 cm) has been thesubject of several research and production initiatives conducted by the Department ofFisheries and the Thailand Research Fund on the basis of its export potential. Severalcommercial grow-out operations have also been constructed and the first commercial harvestsare expected by 2003 or 2004 (Jarayaphand and Papavasit 1996). A notable example isPhuket Abalone Farm in southern Thailand which is expected to produce approximately 10tonnes of abalone per year for consumption in domestic restaurants and for export (PhuketAbalone Farm 2003). Expansion of the abalone farming sector has, however, not yet metexpectations because of a lack of broodstock and seaweed shortages. A smaller number ofhatcheries and grow-out operations for the spotted babylon Babylonia areolata are also beingdeveloped in Thailand, and this species may possess significant future export potential(ChaitanawisutiandKrisnapuntu 1997a, 1997b, 1998).

Shellfish management issues

Aquaculture Development PlanningShellfish aquaculture in Thailand has generally been viewed as a small-scale traditionalactivity that produces seafood for local markets. This perception allowed the industry toevolve in a relatively uncoordinated manner, and the Thai government has had relatively littledirect involvement in shellfish development planning. The recent expansion of Crassostrea


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K. ChaUrmwat et al» Shellfish aquaculture in Thailand 257

belcheri production in southern Thailand has, however, highlighted the potential of shellfishfanning to provide substantial economic benefits in coastal communities. If this potential is tobe realized and expanded to include additional value-added and export production, coastalareas capable of supporting higher value shellfish production must be identified and managedappropriately. Over 60,000 hectares of land along the Gulf of Thailand and the Andaman Seacoasts were previously found to be capable of supporting shellfish culture (Rabanal et al.1977). Unfortunately, many areas such as the Upper Gulf of Thailand have subsequentlybecome unsuitable for the production of export quality shellfish as a result of water qualityconcerns. These problems limit the suitability of many production sites located near majorpopulation centers such as Bangkok, but more remote areas still possess clean growingwaters. Chantaburi and Trat provinces in the eastern region and certain parts of southernThailand could likely support additional high value shellfish production, and biophysicalcapability studies are needed to identify these areas. After the completion of these studies,coastal sites possessing significant potential for shellfish development could be legallydesignated through zoning. Benefits associated with aquaculture zoning include: encouragingthe culture of specific high value species for export production in appropriate areas, andexcluding development activities that are potentially harmful to shellfish production. Zoningwould also provide a venue for increased government involvement in extension activities,growing water management programs, and marketing initiatives.

Hatchery DevelopmentGiven the reliance on traditional grow-out techniques and focus on local markets, it is notsurprising that the production of molluscan bivalves in Thailand continues to rely on naturalseed supplies. Wild spat are generally inexpensive to obtain and abundant, and these factorsrepresent important benefits for small-scale rural aquaculturalists. This approach does,however, leave the industry susceptible to seed shortages when unfavorable environmentalconditions exist in spat collection areas. The situation facing the bivalve farming sector canbe contrasted to the culture of the gastropods H. asinina and B. areolata, both of which arebeing raised to supply high value export markets. A hatchery-based seed production systemfor both species insures seed availability, and provides the potential to enhance productquality which is of critical importance to export markets. Coordinated efforts to transferbivalve hatchery technology from industrialized countries to Thailand were initiated in theearly to mid 1980's (ICLARM 1985), and research on seed production for a variety ofmolluscan species has also been carried out by the Thai Department of Fisheries. A dedicatedcommercial bivalve hatchery system failed to materialize in spite of these efforts because themarket value of green mussels, horse mussels, or cockles within Thailand is simply toolimited. The recent expansion of oyster production could alter this situation, however, and ahigher value species with export potential such as Crassostrea belcheri may finally providethe financial incentive to support the development of commercial bivalve hatcheries inThailand.

Growing Water Quality ManagementThe presence of microbial pathogens in shellfish presents a public health hazard, and marinegrowing waters must be evaluated for pollution, classified into approved harvesting areas,and monitored to insure on-going safety. Areas contaminated by direct fecal wastes,radionucleides or toxic substances should be closed irrespective of the results ofbacteriological analysis. The Fish Inspection and Quality Control Division (FIQD) of theDepartment of Fisheries, Ministry of Agriculture and Cooperatives was established in 1992.One of the main responsibilities of the FIQD is to survey coastal water quality and classifypotential shellfish growing areas. A classification scheme using criteria such as the presence


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of pathogenic bacteria, the incidence of shellfish biotoxins, and the occurrence of heavymetals is currently under development This classification scheme includes three zones (A, Band C) to facilitate the evaluation of growing water quality. Zone "A" includes areas whereshellfish are produced for immediate human consumption, while shellfish from "Zones "B"and Zone "C" are subject to sterilization by boiling or cooking to destroy pathogenic bacteria.Currently only three coastal areas have been assessed under this new classification scheme.Parts of Trat province in the eastern region and Surat Thani province in the southern regionhave been designated Zone "A", while coastal areas of Chumphon province have beendesignated Zone "C".

The FIQD has also established a monitoring program to insure that growing waters inapproved shellfish harvesting areas do not contain harmful microorganisms or toxicsubstances. The surveillance program collects water samples that are evaluated for BOD, pH,ammonia and marine plankton at bi-monthly intervals. Microbiological and biotoxinevaluations are performed monthly and heavy metals are assessed quarterly. An intensivesurvey program has also been established to manage areas that develop serious healthconcerns. The Department of Fisheries co-ordinates a monthly sampling of plankton for thepresence of red tide organisms in the water column and sea bed. Weekly air surveys andperiodic water sampling in coastal areas susceptible to red tides are also performed. Mostphytoplankton blooms in the Gulf of Thailand are not toxic (Chongprasith et al. 1995) andspecies found to bloom most frequently include the blue-green algae Trichodesmiumetythraem and the dinoflagellates Ceratium fiirca and Noctiluca scintillons. The diatomsBacteriastrum, Coscinodiscus, Nitzschia, Hemidiscus, and Rhizosolenia are also foundoccasionally in very high cell densities.

Growing water evaluation and monitoring has only recently been implemented inThailand to minimise public health hazards associated with shellfish consumption. Furtherimprovements in these processes are required to enhance the safety of bivalve molluscsproduced for domestic consumption, and to comply with the shellfish quality assurancerequirements of importing nations in Asia, North America and the European Union. The threeexisting approved growing zones represent a small proportion of the total shellfish farm areain Thailand, and significant resources will be required to expand this system into othercoastal areas that support shellfish aquaculture.

Shellfish Processing and CertificationMany shellfish harvesting and processing operations in Thailand are traditional in nature andcannot meet sanitation standards required for export. This has led to public safety concernswithin importing nations, and the Department of Fisheries implemented a voluntary ban ofThai mollusc exports to Europe after an inspection commission visit in 1998 (EuropeanUnion 2000). Initial measures designed to address these concerns include a "bivalveproduction and sanitation program" organized by the Fish Inspection and Quality ControlDivision. Four fish inspection centers were established in Bangkok, Samut Sakom, Songkla,and Surat Thani provinces. These centers are responsible for the inspection and certificationof bivalve mollusc processing establishments and laboratory testing of seafood products. Allof the centres perform microbiological and heavy metals analysis on the flesh of bivalves(typically the short-necked clam Paphia undulata) and the Bangkok center acts as the centrallaboratory for biotoxins analysis. The Eastern Marine Fisheries Development Center inRayong province performs microbiological and heavy metal tests of bivalve flesh from theTrat harvesting area.

The Thai government has also put significant resources into improving sanitaryconditions at landing sites, de-shelling stations, and processing plants. Thai governmentagencies have worked in close collaboration with the Thai Frozen Food Association, the Thai


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K. Chaiermwat et ci» Shellfish aquaculture in Thailand 259

Food Processor's Association, and Fish Marketing Organizations to upgrade processingfacilities, improve water treatment systems, implement safe product handling practices, andorganize regular sanitary inspections. A list of de-shelling stations and bivalve processingplants that are in compliance with European Union directives was established, and theseimproved facilities were open to auditing by European Union inspectors. Depuration policiesfor bivalves destined for export have been implemented in conjunction with researchdesigned to determine the most appropriate conditions for these operations in Thailand(Areerat and Gannarong 2000; Gannarong et al. 2001). Seafood HACCP plans have also beenused to enhance public safety and export quality control, and the design and implementationof HACCP plans within processing plants has been given a high priority by both thegovernment and private sectors in Thailand (Kirativiriyaporn 2000).

Although significant improvements have been achieved in the areas of seafood safetyand sanitation in Thailand, these advances have been restricted to a small number ofrelatively sophisticated commercial operations exporting wild or farmed molluscs to marketsin Japan, Europe and North America. A far larger number of small-scale traditionalbusinesses supply molluscs to the Thai domestic market, and these operations regularlyharvest, process, and market bivalves in conditions that have the potential to compromisepublic safety. Extending safe and hygienic shellfish processing practices into the domesticsector presents a significant challenge because many small-scale aquaculturalists in ruralThailand possess limited skills and education. Extension programs directed at small-scaleproducers could enhance the quality and safety of molluscs consumed in Thailand, andsuccessful implementation of these programs could potentially allow this group to accessmore lucrative export markets.

Conclusions

Aquaculture now represents the majority of shellfish produced in Thailand each year. Lowervalue crops such as the green mussel still provide a large proportion of the total annualfarmed harvest, but oyster and blood cockle production has expanded dramatically inresponse to higher rates of return for these species. Although the shellfish farming sector hasexpanded, production is still largely restricted to local markets as a result of severalconstraints. Consumer safety and public health issues represent a significant impediment toexpanding international distribution. In particular, the implementation of growing watermanagement measures, product testing procedures, and sanitation protocols must be appliedto a much larger segment of the industry. Financial and technical support from the Thaigovernment is also required to spread knowledge of improved husbandry techniques andsanitary management procedures to a much wider group of shellfish growers than has beenattempted to date. Improvements in production, processing and marketing are important, butthe ultimate fate of the Thai shellfish industry lies in maintaining environmental conditions inkey productions areas such as Surat Thani, Phangnga, Chantaburi and Trat. Excellentshellfish grounds in the Upper Gulf of Thailand have been degraded by water pollution inrecent years, and other important growing areas could also be affected unless more stringentenvironmental control measures are implemented by the Thai government and localauthorities.

Acknowledgements

The Thailand Aquaculture Management Project at Burapha University provided technicalsupport during the preparation of this manuscript. Graphs included in this paper were


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prepared by Belinda Ward-Campbell of Burapha University Department of BiologicalSciences, and maps were prepared by Ole Hagan of the University of Victoria Department ofGeography.

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