Coastal Shrimp Aquaculture in Thailand: Key Issues for Research

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during the rainy season, some deterioration of inshore water quality has been noted attimes.Elsewhere, and notably in the Upper Gulf of Thailand, the nutrient loads fromcoastal shrimp farms have been shown to be insignificant when compared to othersources of the coastal nutrient loads, particularly nitrogen and phosphorus from agriculturaland domestic sources (Pollution Control Department 1997).Treatment of effluent waterOn smaller farms, most effluent water is discharged without treatment. Wherewater is treated, settlement ponds are the most commonly used method. These areeffective at decreasing the levels of phosphorus, dissolved nitrogen and suspendedsolids, but BOD can increase because of the high nutrient levels in the ponds andbecause of phytoplankton blooms (Briggs and Funge-Smith 1994). On larger farms,greater than 50 rai, Thai Government regulations that came into effect in 1991 stipulatethat effluent must be treated via settlement ponds of a size equivalent to or largerthan 10% of the total farm area.In one study, the required size of settlement ponds was calculated from measurementsof the settling velocity of particulate matter in the effluent (Smith 1995). A settlementpond of 0.75 ha for an effluent discharge of 1 m 3 /s was found to be suitable.The study showed that more than 90% of the diatomaceous silica (in diatom shells)that accumulated in ponds was derived from the weathering of clay from pond walls.Also, the effluent contained a high level of inorganic material that was eroded fromthe soil in the ponds. Consequently, much can be done to reduce sediment loadingsby improving soil conservation on the farm, and particularly through the use of linersand other methods to keep pond walls intact.Biological methods of water treatment have been investigated in Thailand and elsewhere.The green mussel Perna viridis has been trialled (DOF 1992) with some successat reducing BOD, organic solids and phytoplankton. This mussel, however, is sensitiveto salinity fluctuations and its production of faeces and pseudo-faeces may add to sedimentloads. The seaweed Gracilaria has been grown in conjunction with green musselsand shown to reduce soluble nutrients. Unfortunately it is also sensitive to salinity fluctuations,and in turbid and eutrophic pond effluent suffers from light limitation, as wellas smothering by sediment and epiphytic microbial growth. Currently under investigationat the Petchaburi Coastal Aquaculture Centre is the use of a native seagrass.Various groups of bacteria are under examination to assess their usefulness in acceleratingthe breakdown of pond wastes (Keawchum 1993).Sediment disposalSediment from ponds is usually removed at the completion of the productioncycle. NACA (1994a) found that 36% of surveyed farms dumped sediment along thepond dykes, 36% in designated sediment disposal areas, and the other farms disposedof it elsewhere. Discharge of pond sediment into water bodies has the potential toaffect them in a similar way to effluent water, but there is a high degree of awarenessamong farmers of this problem and most places of disposal are now away fromwaterways. Because it is high in salinity, it is not colonised readily by most plantsuntil the rain has had chance to wash away some of the salt, which usually takes"'
around two years. Some farmers recycle the sediment after two years to repair dykesand pond walls.Self-pollutionThe discharge of effluent water into the same canals used for water supply meansthat farms may pollute their own and their neighbour’s supply, contributing to waterquality deterioration. In recognition of the problem, DOF and the Irrigation Departmentshave embarked on a number of engineering works aimed at separating effluentdrains from intakes. In Surat Thani Province, some farmers have attempted toaddress the problem of self-pollution with a flag system that warns neighbours wheneffluent discharge is in progress (MacIntosh and Phillips 1992). In other areas,farmers have stipulated times for effluent release coordinated with the tides. DOF istrying to further promote such coordination between farms. In the south, the AquastarCompany constructed large seawater intakes, 200 m out to sea, to service its contractedfarms. These intakes are able to access cleaner water than can be obtainedcloser to shore.Spread of shrimp diseaseDisease-causing micro-organisms discharged in effluent water may be spread tonearby farms or to organisms in the natural environment. Smith (1993, 1998) hasshown that the organisms of the family Vibrionaceae are significantly higher in mangrovesediments close to farms compared to those at a distance. This finding suggeststhat farms should maximise the distance between their intake point and their effluentcanal or their neighbours. However, in general the interactions between farm location,density and shrimp disease occurrence are poorly understood, and more researchis needed to develop guidelines on this subject.Salinisation of land and waterIn some places, saline effluent water and seepage from ponds have contributed toyear-round salinisation of canals that were previously saline only in the driest periodsof the year. Where this occurs, traditional agriculture and sometimes drinking waterhave been affected. Although a number of other factors have contributed to salinisationof land and water in Thailand, where it occurs in shrimp farming areas, thesefarms tend to be the obvious focus for blame. Conflicts between non-shrimp farmingresidents and shrimp farmers in some coastal areas of Thailand were common,although these problems are fairly rare today. Of more recent concern are the effectsof inland shrimp farming on agricultural areas, although there is a lack of scientificstudy on this particular problem (Lin 1998).In Ranot District in southern Thailand, the watertable dropped from 3 m to 7 mbetween 1989 and 1991. This was attributed not to shrimp farming, but to deforestationof catchment areas resulting in decreased percolation of water into the soil,and decreasing rainfall over the period (NACA 1994a). This shows the complexityof judging environmental change and the need to consider the potential impacts ofshrimp culture within the context of all activities in the coastal area of the watershed."(
Page 8 and 9: !The 1994 Workshop had a working hy
Page 11 and 12: !The Workshop at Hat Yai, SongkhlaA
Page 13 and 14: !ReferenceSmith, P.T., ed.. 1999. T
Page 15 and 16: !Shrimp Farming in ThailandOver the
Page 18 and 19: ! !Table 1. World production (# 1,0
Page 20 and 21: !Domestic and world demandJapan is
Page 22 and 23: !Intensification of farms has been
Page 24 and 25: !no significant difference between
Page 26 and 27: !Production Practices and Technique
Page 28 and 29: !use water which is almost fresh (F
Page 30 and 31: !mended quantities for application
Page 32 and 33: !the biological processes in sedime
Page 34 and 35: !factors (Fegan 1994). Environmenta
Page 36 and 37: !Acid sulphate soils occur in most
Page 40 and 41: Land subsidenceCoastal land subside
Page 42 and 43: first when an area becomes environm
Page 44 and 45: !Administration. Their work has inv
Page 46 and 47: agriculture, selects coastal land p
Page 48 and 49: Sustainability, Sustainable Develop
Page 50 and 51: cultural and environmental asset va
Page 52 and 53: $+Table 12. (cont’d) Impediments
Page 54 and 55: $#Table 12. (cont’d) Impediments
Page 56 and 57: $%Table 12. (cont’d) Impediments
Page 58 and 59: capacities of alternative organisms
Page 60 and 61: sources. This is one of the greates
Page 62 and 63: Table 13. (cont’d) Summary of the
Page 64 and 65: Boonyapiwat, S. 1989. Species of ph
Page 66 and 67: Katesombun, B. 1992. Aquaculture pr
Page 68 and 69: Sirisup, S. 1988 Socio-economic cha
Page 70 and 71: !In the preliminary analysis, the s
Page 72 and 73: !until all variables had been teste
Page 74 and 75: !quality problem over the past 3 ye
Page 76 and 77: !Figure 1. Characterisation of prov
Page 78 and 79: !Variables Contributing to Shrimp P
Page 80 and 81: !Figure 5. Relationship between ave
Page 82 and 83: !southern). The linear regression m
Page 84 and 85: !Appendix. Results of logistic regr
Page 86 and 87: !2) Trat ProvinceClassification tab
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!Chi-square df significanceModel Ch
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!8) Satun ProvinceClassification ta
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!Variables in the equationConstant
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!A total of 49 participants were in
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! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !Fi
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!All issues are listed in Appendice
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!!were short term and one issue was
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!reared broodstock (issue 71). They
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!!Two participants commented that i
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mation transfer and training. This
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108Appendix 1. (cont’d) Descripti
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112Appendix 2. Descriptive statisti
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Appendix 5. (cont’d) Descriptive
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Appendix 7. Descriptive statistics
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Appendix 7. (cont’d) Descriptive
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!ParticipantsAustraliaDr Paul T. Sm
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Coastal Shrimp Aquaculture in Thailand: Key Issues for Research

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