Environmental Assessment of the Rapid Expansion of Intensive Shrimp Farming in Tam Giang - Cau Hai Lagoon, Central Viet Nam

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1 駒澤地理 No.49 pp. 1 ~ 9, 2013 Komazawa Journal of Geography Environmental Assessment of the Rapid Expansion of Intensive Shrimp Farming in Tam Giang - Cau Hai Lagoon, Central Viet Nam Yukihiro HIRAI *, Tetsuo SATOH *, Yasushi TANAKA *, Nguyen Van LAP ** and Ta Thi Kim OANH ** In Thua Thien Hue province both the cultured area and the production of shrimp increased rapidly from 1999 to But during following five years from 2005 to 2009, the cultured area decreased approximately 40 % though the production increased approximately 25 % in the same period. Namely for these ten years from 1999 to 2009, a rapid expansion of shrimp farming and the transition to intensive farming have occurred in this area. In this study, we clarified the actual process of the expansion and transition to the intensive farming of shrimp culture as a local level in Vinh An Commune, Phu Vang district, which are located in the southeastern part of Tam Giang lagoon and a very intensive farming has been developed rapidly in the last decade. And we made some assessment of lagoon environments from the viewpoints of sustainable resource management. In Vinh An Commune shrimp farming ponds of Sandbank type in the lagoon and Paddy field type in the littoral lowland have spread rapidly after 1999, which caused further water pollution of the lagoon. On the other hand farming pond of Sand dune type on the coastal sand dune began in Vinh An Commune after This type of shrimp farming is very intensive one, which culture density is high markedly, and the cultured species is different from the others. This type of shrimp farming may cause shrinkage of the groundwater under the sand dunes. There is a possibility of leakage of saline water from a farming pond into the groundwater. We need to check the water quality of the groundwater as well as the lagoon water to develop the better operational management for the sustainable aquaculture in this area. Keywords: Tam Giang lagoon, shrimp culture, intensive farming, shrinkage of groundwater, sustainable aquaculture Tam Giang Lagoon, lying along the coast of Thua Thien Hue province in Central Viet Nam, has undergone a rapid expansion of shrimp aquaculture over the last decade. The amount of production of the cultured shrimp in Thua Thien Hue province was 365 ton in 1999, and it increased to 4,268 tons in Figure 1 is the cultured area of shrimp and its production from 1996 through 2011 in Thua Thien Hue *Department of Geography, Faculty of Literature, Komazawa University **HCMC Institute of Resources Geography, Vietnam Academy of Science and Technology 1

2 10 3 ton Production of shrimp (left axis) Area of water surface of shrimp culture (right axis) 10 3 ha Fig. 1 Production and cultured area of shrimp in Thua Thien Hue Province. Source: Statistical Yearbook (Thua Thien hue Statistical Office, 2001,2002,2007,2012) Province. The cultured area increased rapidly during the six years from 1999 to 2004, and the production of the shrimp also increased during the five years from 2000 to The cultured area in 1998 was 931ha, and expanded to 3,998 ha in 2004, more than 4 times of that in The production was 365 tons in 1999, and increased to 3,443 tons, approximately 10 times of that in So we call the period from 1999 to 2004 when both the cultured area and the production increased rapidly the expansion period of shrimp farming.but after 2004 the cultured area decreased approximately 40 % during the five years from 2005 to In contrast, the production increased approximately 25 % from 3,443 tons to 4,268 tons in the same period. The reason why the production increased though the cultured area decreased is that the land productivity of the shrimp rose from 0.86 tons/ha to 1.81 tons / ha, approximately two times. In other words, it is supposed that the previous extensive or semi-intensive culture has switched to intensive culture during this period. So we call the period from 2005 to 2009 when the production increased though the cultured area decreased the transition period to intensive farming. At present, some different types of shrimp farming ponds are seen in the Tam Giang Lagoon and its surrounding area. Among them, intensive shrimp farming ponds are particularly spread not only in the lakeside of the lagoon but also in the former paddy fields and on the coastal sand dune. As a result of such rapid expansion and transition to intensive shrimp farming in this area, some environmental problems have occurred, such as the destruction and the disappearance of the aquatic plants in the lakefront, water pollution of the lagoon, salt water invasion into the groundwater in the area adjacent 2

3 Fig. 2 Tam Giang Cau Hai Lagoon and the study area. Background of right figure is a false color image of ALOS AVENIR-2 acquired in to shrimp ponds and so on Hirai, 2009 a, 2009 b In this study, we intended to clarify the actual process of the expansion and transition to the intensive farming of shrimp culture in a commune level, and we shall make some assessment of lagoon environments from the viewpoints of sustainable resource management in this area. Then we have researched in the Vinh An Commune, which are located in the southeastern part of Tam Giang lagoon, where the intensive shrimp farming have been developed rapidly in the last decade (Fig. 2). 2 Methodology To identify the geographical distribution and the process of development of shrimp farming, we have prepared some kinds of satellite images, such as Landsat 7 - ETM, QuickBird and ALOS - AVNIR - 2. Especially we compared the ALOS AVNIR - 2 false color image acquired on June 30, 2009 with the Landsat ETM false color image acquired on Sep. 1, 1999 to discuss the process of development of shrimp farming during the last decade in the study are. We have conducted a field survey during four days from March 19 to 22,2010 to check the characteristics of the facilities of each type of shrimp farming ponds. At the same time we made some interviews to the owners of shrimp farming ponds about the way of their operational management. 3

4 Based on the analysis of the satellite images and the results of the field survey, we classified shrimp farming ponds into 6 different types, a. ~ f. as below, in terms of farming facilities and operational management (Table 1, after Hirai et al., 2010) a. : One of the traditional ways of aquaculture derived from net fishing. After the big flooding in 1999 they have closed the fishing net completely to raise the fry shrimp in it (Hirai, 2009 b). b. : Ponds surrounded by bamboo and mud in shallow lagoon bottom (Okamoto et al., 2009), shaped square. c. : Ponds surrounded by bamboo and mud or net, located along the shoreline of lagoon, and shaped rectangular. One side of a pond faced to lagoon is screened by net. So the water in the shrimp pond always interchanges with lagoon water. d. : Ponds dug on a sandbank in lagoon, 0.5 ~ 1 m in depth, surrounded by bamboo and mud or stone. e. : Ponds dug in former paddy field along the shoreline of lagoon, about 1 m in depth, shaped thin rectangular. f. : Large-scale ponds dung on coastal sand dune, 1.5 ~2.5 m in depth, surrounded by sand dyke covered thin waterproof sheet. They raise Litopenaeus vannamei (Whiteleg shrimp) in the ponds, not monodon (Black tiger prawn) as in the other types of shrimp ponds. Farming density is very high about 100~170 shrimps/m 2, which is about 15 ~ 30 times of the paddy field type. 4

5 Table 1 Characteristics of farming facilities and operation in six types of shrimp farming (partly modified Hirai et al., 2010). Characteristics of farming facilities Type of a shrimp farming Shape of a pond a. Net-enclosure Triangle, square or pentagon Image of QuickBird (height and length is 300 m each) Location (Height above sea level) Depth of a pond Area of a pond Structure of a pond Characteristics of operation Water for farming Species of shrimp Drainage (to where) Farming density In a lagoon (H=0m) D = m To lagoon A = ab. 1 ha bamboo and net monodon (Black tiger prawn), crab and fish (Unknown) b. Earth pond Square c. Lakeside type Rectangular d. Sandbank type Square or pentagon e. Paddy field type Thin rectangular f. Sand dune type Square or rectangular (same size) In a lagoon (H=0m) D = ab. 0.5 m A = ha bamboo and mud Along the shore of lagoon (H=0m) D = ab. 0.5 m A = ab. 0.2 ha bamboo and mud or net To lagoon Average farming area per one operator Crop in Ab. 1 ha succession after 3 months raising of fry shrimp (twice) ab. 200 kg / ha / year (No data) monodon (Black tiger prawn) (No data) ha (Unknown) To lagoon monodon (Black tiger prawn), crab and fish (Unknown) On a sandbar (H=0m) D = m To lagoon A = ha bamboo and mud or stone Lacustrine lowland (H=1 2 m) former paddy field D = ab. 1 m A = ab. 0.2 ha mud dyke Number of crops per year Crop yield per ha kg / year To lagoon On the sand Sea water and dune (H=10 m) groundwater D = m A = ha To sea Surrounded by sand dyke covered by thin waterproofed sheet 5 Crop in Ab. 1ha succession after 2 months raising of fry shrimp (three times) ab. 400 kg / ha / year 2 times ha 6 ponds monodon (Black time ha tiger prawn) kg / ha / year 3 4 prawns / m2 2 times ha monodon (Black time 2009 tiger prawn) kg / ha / year prawns / m Litopenaeus vannamei (Whiteleg shrimp) shrimps / m2 Twice or three times 13,000 20,000 kg / ha / year 0.3 ha 30 pond = 9 ha 0.25 ha 28ponds 7 ha 0.4 ha 24ponds=10 ha

6 2) Geographical distribution and the process of development of shrimp farming Figure 3 shows the geographical distribution of the shrimp farming ponds of each type identified by the satellite image acquired on September 1, 1999 and June 30, 2009 respectively. For ten years from 1999 through 2009, the shrimp farming ponds have developed in the former paddy fields (e. type), on the sandbar in the lagoon (d. type) and furthermore on the coastal sand dune ( f. type) as well as the lakefront of the lagoon (c. type). In 1999, some shrimp farming ponds of c. type or d. type were seen at several places in the lakefront of the lagoon in Vinh An Commune. However, in 2009, the lakefront of the lagoon is almost occupied by these two types of farming pond. On the other hand some large-scale farming ponds can be identified on the coastal sand dune by the analysis of the satellite image acquired in This type of shrimp farming pond started since 2003 in the area of 10ha at first. Total area of shrimp farming ponds on the sand dune is 27 ha by three owners. And new farming ponds of 5 ha are getting ready in 2012 on the adjacent sand dune. Namely the shrimp farming ponds of c. type and e. type spread rapidly in the lakefront of the lagoon after 1999 in Vinh An Commune. This rapid expansion of the shrimp ponds corresponds with the expansion period of shrimp farming in the whole Thua Thien Hue province. a b! #" Fig. 3 Geographical distribution of each type of shrimp pond in Vinh An Commune in 1999 and in 2009 (partly modified Hirai et al., 2010). Background satellite images are (a) Landsat ETM false color image acquired on Sep. 1, 1999, (b) ALOS AVNIR-2 false color image acquired on Jun. 30,

7 In addition, a new type of shrimp farming (f. type) began on the coastal sand dune in Vinh An Commune after An area of this type of farming pond is larger than the other type of shrimp pond with about 0.3 ha ha, and the depth is deeper than the others with m. And the cultivating species in this type is Whiteleg shrimp that is different from Black tiger prawn in other type of farming ponds, as mentioned in 3.1). This type of farming is very intensive culture, 15 ~ 30 times is higher in the farming density than e. type. It is after 2003 that such very intensive farming spread in Vinh An Commune. It is supposed that the development of this new type of shrimp farming on the sand dune is one of the actual situations related to the transition period to intensive farming. Overcrowded installation of farming facilities in and along the littoral zone has deteriorated water quality in the lagoons. Especially intensive aquaculture spreading over the lacustrine lowlands has caused further water pollution in the lagoons and outbreaks of shrimp diseases. District office has counseled the owners of the shrimp farming to crop once a year not twice since Recent development of large-scale intensive shrimp farming on the sand dunes may cause shrinkage of the groundwater under the sand dunes. In these farming ponds on the sand dunes, they draw both seawater and the groundwater under the sand dune to breed the shrimp. The quantity of drawing groundwater is nearly 10 tons per 1ha by one culture. So it is supposed that the total consumption of the groundwater in this area is approximately 800,000 tons, based on the area and the annual crop number of times in each farming pond. The bottom and the dike around a farming pond on the sand dune are covered with a plastic sheet of thickness 0.15 ~0.3 mm. This plastic sheet will be changed every 1 ~ 3 year. But we could see that the plastic sheet of the bottom of a pond is really torn here and there, which some of them are repaired, and then a large quantity of saline water of in salinity will filled up in the pond. So there is a possibility of leakage of saline water from a farming pond into the groundwater. Moreover, the saline water is also penetrated to groundwater through the drainage ditches of wastewater from farming pond. In this study, we classified shrimp culture in six types in terms of farming facility and operational management. Then we clarified geographical distribution of each type of farming pond through on-site survey and analysis of two different satellite images taken at 1999 and As a result, a development process of the shrimp farming in Vinh An Commune is clarified. Namely shrimp farming ponds of d. type (Sandbank type), and e. type (Paddy field type) have spread rapidly mainly in the lakefront of the lagoon after 1999, which caused further water pollution of the lagoon (Figure 4,1). On the other hand farming pond of f. type (Sand dune type) began on the coastal sand dune of Vinh An Commune, Phu Vang district after This type of shrimp farming is very intensive, which culture density is high markedly, and the cultured species is different from the others. This type of shrimp farming may cause shrinkage of the groundwater under the sand dunes. And there is also a possibility of leakage of 7

8 Fig. 4 Schematic process of development of shrimp farming and some environmental issues in Vinh An Commune (The location of this cross section is shown in Figure 3). saline water from a farming pond into the groundwater (Figure 4,2). We need to check the water quality of the groundwater as well as the lagoon water in detail to develop the better operational management for the sustainable aquaculture in this area. At the same time it is necessary to make clear the present extent of the groundwater under the sand dunes. It is also important to describe the current groundwater use by the local people, as well as the usage of the groundwater for the shrimp farming to develop the sustainable resource management in this area. The authors would like to express their deep appreciation to Dr. Tran Ngoc Nam, director of the department of Science and Technology of Thua Thien Hue Province for giving an opportunity to make fieldwork. This study was funded by Grant-in-aid from Tokyo Geographical Society and Institute for Applied Geography, Komazawa University. This is a part of research project between Komazawa University and HCMC Institute of Resources Geography, Viet Nam Academy of Science and Technology. Hirai, Y. (2009 a) : Monitoring environmental changes of lagoon area with high resolution satellite images. Regional 8

9 Views, 22, (in Japanese). Hirai, Y. (2009 b) : What happened in the lagoon in Viet Nam? Geography (Chiri), 54 (8), (in Japanese). Hirai, Y., Sato, T. and Tanaka, Y. (2010) : Some environmental issues accompanying the rapid expansion of shrimp farming in Tam Giang Lagoon, Central Vie Nam: An environmental assessment based on an analysis using high-resolution satellite images. Journal of Geography, 119 (5), (in Japanese with English abstract). Okamoto, Y., Tanaka, U., Mizuno, K and Nguyen, P. N. (2009) : Seasonal Change of Sediment Condition in Aquaculture Area and Fishery Resource Management in Sam - A Truyen Lagoon, Central Vietnam. Journal of the Japanese Agricultural Systems Society, 25, (in Japanese with English abstract). Thua Thien Hue Statistical Office (2012) : Statistical Yearbook 2011.Thua Thien Hue Statistical Office, 355p. + Statistical Yearbook 2007, Statistical Yearbook 2002 and Statistical Yearbook