In Mekong Delta’s southern provinces, Bac Lieu and Ca Mau, the rural livelihoods are mainly based on fisheries and shrimp farming. The main shrimp farming systems are intensive and improved extensive, of which the last may be integrated or associated with mangrove. Integrated means that most ponds are canals amidst stretches of mangrove, while in associated shrimp-mangrove systems the mangrove forest is a large plot clearly separated from the pond areas.
Decision-making in shrimp farming considers several risks and uncertainties. Next to the disease risks and ecological uncertainties farmers are subject to economic uncertainties (market prices of inputs and shrimp), social, political and institutional processes. Though all are pursuing increased incomes, this multitude of factors means that the livelihood history of households of shrimp farmers and fishers may follow different pathways. In 2009, about approximately 70% of the households reported that shrimp farming today was riskier than five years ago. Farmers cited environmental problems associated with shrimp disease as their main cause of failure. To them, shrimp diseases are caused by deforestation, soil degradation, and pollution from sewage water and sediments in the canals, by salinization, and the use of unqualified shrimp seed. The water is polluted because the canals act as both clean water supply and wastewater sinks. Consequently, disease agents in the effluents from one farm are transmitted to neighbouring farms. This problem is observed both in aquaculture systems with and without mangroves, in both extensive and intensive farming.
Households in the mangrove-shrimp integrated system appreciated the water infrastructure more than households in the non-mangrove system (Table 1). Water quality in the intensive non-cluster systems scored worse. These systems dominated in areas where mangroves were totally destroyed after 1975; the water infrastructure consisted of narrow canals causing downstream wastewater pollution, water shortages in the dry season, and thus increased risk of transmission of shrimp disease. Farm density here is high also, thus reducing the capacity of the environment to function as bio-filter for the wastewater from the ponds.
Shrimp diseases occur during the whole year but systems experience the highest risk in different periods of weather change. The extensive system with mangrove suffers mostly when the dry and rainy seasons are shifting. According to farmers, the rains have become more unpredictably in recent years, which has made shrimp farming more vulnerable to failure.