Effects of mangrove leaf litters on the integrated mangrove : shrimp farming systems in Ca Mau Province, Vietnam | |
| Author | Tran Ngoc Hai |
| Call Number | AIT Diss. no.AQ-05-05 |
| Subject(s) | Mangrove ecology--Vietnam--Ca Mau Province Shrimp culture--Vietnam--Ca Mau Province |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AQ-05-05 |
| Abstract | In response to the rapid destruction of mangrove forestry for shrimp culture during 19801995 in Ca Mau province of Vietnam, several policies and regulations have been issued and implemented by the Vietnamese government to reforest and protect mangroves. The integrated mangrove--shrimp farming system was promoted by the government to ensure both mangrove conservation and income generation. This system was said to have several technological and socio-economical problems such as overload of leaf litters, water quality deterioration and difficulties in management of shrimp ponds. This research study, therefore, was designed to evaluate current status of integrated mangrove-shrimp farming system in Ca Mau province in Southern Vietnam in terms of technology, socio-economics. management strategies and policies. The effects of mangrove leaf litters to water quality parameters and shrimp growth and survival were studied under both on-farm and laboratory conditions. Recommendations were then developed to enhance the sustainability of the current mangrove-shrimp farming system was developed using the research finding of this study. The results of a questionnaire survey of 212 households, key informant survey and secondary data showed that there were important changes in the government policies to allow decentralization, socialization, participation and diversification in the management of the mangrove forestry and the integrated mangrove-shrimp fanning systems. There were no significant differences in production and economic benefits among different integrated mangrove-shrimp fanning systems and improved extensive shrimp farming systems. Fauns with different mangrove species did not result in significantly different aquaculture production and net incomes. Farms with mangrove over 15 years old had slight reduction in aquaculture production and income. Farms with polyculture of aquaculture species (shrimp, crabs, cockle and fish) had relatively higher production and profits.. However, stepwise regression analysis showed that only mangrove to total farm area ratio had significantly negative effect on aquaculture productivity and income. Based on total area, farms with mangrove cover over 60% of the total farm area had slightly lower aquaculture production. Shrimp stocking density had significantly positive effect on both aquaculture productivity and income Leaf litter production, accumulation, and decomposition of different-aged mangrove species showed that the mean litter production of 5, 10 and 15-year old Rhizophora and Avicennia-Excoecaria mangroves were 72, 89, 62 and 30 g nm-` month 1, respectively. Leaf litter accumulation in ponds were significantly lower than those on the mangrove platform (P<0.05) and litter accumulation rate of mixed Avicennia and Excoecaria both on the platform and ponds were significantly lower than the Rhizophora species (P<0.05). The age of Rhizophora did not significantly affect leaf litter accumulation in ponds. Leaf litter accumulations in the middle and the back ends of the ponds were significantly higher than those in the front ends of the ponds. Regression coefficients of leaf litter production to leaf litter accumulation on mangrove platform and on ponds were found to be very low. Half life for decay of Avicennia, Excoecaria, Rlrizophora and Acacia in the pond bottom and on wet mangrove platform were 50 and 55 days, 62 and 91 days, 75 and 133 days and 257 and 408 days, respectively. On-farm survey of water quality dynamics showed that most of water quality parameters among the different mangrove farming systems were not significantly different from one another. Water quality parameters were within acceptable ranges for shrimp culture. Water quality parameters and natural shrimp yield showed strong variations with seasons. However, there was no significant difference in natural shrimp yields among the farms with different mangrove species expect that Napa farms which had significantly higher production. The laboratory experiments on effect of leaf litter load and water aeration and exchange regimes on water quality and shrimp growth and survival showed that high leaf loading rates significantly reduced dissolved oxygen (DO) and survival rates of shrimp in the nonaerated treatments, and all shrimps died after 2 days in the treatments of above 0.5 g Ui loading rate. Leaf-litter loads significantly increased tannin, chemical oxygen demand (COD), H2S, and pH in the aerated treatments. Stepwise regression analysis showed COD, Tannin and H2S concentrations negatively affected shrimp growth in the aerated treatments. Tannin concentrations were found to be highest in the treatments with Excoecaria (32 mg L'') and Avicennia (24 mg L-i) leaves. However, there were no significant differences in growth and survival rates of shrimp among the aerobic treatments loaded with different leaf types. The results also showed that moderate load of mangrove leaves could play an important role in promoting shrimp growth and survival in aerobic condition. Mangrove leaves at a loading rate of 1 g L-1 showed positively influenced both the survival and growth rates. However, further studies under field conditions are necessary to confirm this observation. High rate of water exchange (75% biweekly) rates reduced total ammonium nitrogen (TAN) and Chemical Oxygen Demand (COD) but only nitrite content was significant reduced. High water exchange rate (75%) significantly improved biomass, growth and survival rate of shrimps. Shrimp biommass, BW, SGR and survival rate had negative relationship with H2S, TAN and Nitrite contents. In conclusion, coastal zone farmers in Southern Vietnam have been encouraged by the government to replant and protect mangroves in Ca Mau province using a series of policies and regulations to promote the integrated mangrove-shrimp farming system. This system has been shown to be an important economic activity that assists farmers' livelihood. However, the existing integrated mangrove-shrimp farming systems also have several technical, socio-economical and environmental problems and are lack of natural benefit for both mangrove and shrimps. The majority of farmers desire to change the system to take advantages of recent technical advances and to receive more economic benefit. However, no studies have been conducted to improve this farming system taking tilt functions of both mangroves and aquaculture sub-systems into account. Therefore there is an urgent need to modify existing integrated shrimp-mangrove-farming system to benefit both subsystems |
| Year | 2005 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AQ-05-05 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Aquaculture and Aquatic Resources Management (AQ) |
| Chairperson(s) | Yakupitiyage, Amararatne; |
| Examination Committee(s) | Preeda Parkpian;Yi, Yang;Lin, Chang Kwei;Somsak Boromthanarat,; |
| Scholarship Donor(s) | Government of Denmark (DANIDA); |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2005 |