40 MARCH 2013 • WORLD AQUACULTURE • WWW.WAS.ORG by the worst tropical cyclone (Sidr; category 4) in 10 years, killing around 4,000 people. In May 2008, Cyclone Nargis devastated coastal life in Bangladesh. In April 2009, Cyclone Bijli veered away from the southern coast of the country, without causing any serious damage. One month later, Cyclone Aila slammed into southwest Bangladesh, leaving hundreds of thousands of people homeless after the storm surge washed away villages, roads and livestock, with a death toll of around 100 people. It is widely recognized that the frequency of monsoon depressions and cyclones in the Bay of Bengal has increased. The prawn sector is the most vulnerable to climate change. This threat from climate change could have dramatic consequences for the economy of Bangladesh. Table 1 outlines possible impacts of climate change on the prawn sector in Bangladesh. Effects of Salinity Increased salinity has caused negative effects on freshwater prawn production in gher systems, including fish, rice, vegetables and fruits. Most prawn farmers fear the intrusion of salinity as the main barrier to prawn farming in rice fields (Fig. 4). The increasing trend of salinity in prawn farming areas is leading to reduced interest in cultivating prawn and various agricultural crops. Increased salinity has also caused disease problems in farmed prawns, particularly viral and luminescent bacterial infections, including black spot, white spot, and yellow-head diseases. Native freshwater fish species in prawn farming areas are gradually declining. Local native fish species have declined and some have disappeared. Rice production also has dropped because ghers have been inundated by saline water, causing increased soil salinity. Decreased rice production has meant reduced availability of paddy straw for cooking fuel, building materials for housing, and fodder for cattle. Cattle raising has decreased because of the reduction in available grazing land and, as a result, there is decreased availability of cow dung, milk and meat. Production of poultry has declined in prawn farming areas and mortality of chickens is high in areas where salinity is very high. Raising ducks has become difficult because of increased salinity and the associated reduction in the availability of snails used for duck feed. The reduction of rice fields and water salinity have negatively affected populations of the Indian bullfrog Rana tigrina, known as the ‘farmer’s friend,’ which plays an important role in rice farming systems as a pest controller. The abundance of other wildlife, including aquatic birds, crabs, mollusks, oysters and turtles have declined gradually. Another constraint to crop production, including vegetables, is the increase in soil salinity levels from prolonged inundation of the land by saline water. The effect of salinity not only affects vegetable crops but impacts on fruits (known as farmers’ saving banks) are now well recognized. Salt-sensitive fruit trees, such as guava, banana, papaya, plum, mango, date palm, jackfruit, blackberry and palm are disappearing gradually. Health Concerns In prawn farming communities, human health has been FIGURE 4. A farmer with prawn is concerned about salinity intrusion. FIGURE 3. Inundated gher used for prawn farming.
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