WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2017 49 fattening in ponds/ghers is selective or progressive harvesting and restocking (Santos 2014). The average annual production in the fattening system is about 3000 kg/ha and annual net income is US$ 15,833/ha with only 60-65 percent survival. Furthermore, 15 percent extra income can be added by finfish (especially tilapia) and shrimp production in a polyculture system. Monthly income of crab fatteners has increased by 39 percent, ranging from US$ 99-124 (Rahman et al. 2015). Mortality at stocking because of poor quality and handling of crab seeds and lack of knowledge on best management practices hampers production and income in crab farming systems. Nevertheless, the system has a demonstrated reputation to vulnerable impoverished households and small-scale farmers. Crab fattening offers comparatively higher returns than other aquaculture practices in coastal areas. The short production time reduces the risk of losing crabs to disease. There is a higher survival rate for fattening (>90 percent) than grow-out systems (40 percent). Most crab fatteners in coastal zones are Hindu (73.7 percent) and the balance are Muslim (26.3 percent) (Rahman et al. 2015). Grow-out Culture Some farmers practice grow-out by stocking small (1-50 g) crab seed (Fig. 3) in ponds and ghers to grow to market size. Some independent coastal marginalized men and women crab fishermen collect crab seeds with a push net in the marshes of the Sundarbans mangrove forest, estuaries, canals, and tidal rivers during January to late March and sell to grow-out farmers at the low price of US$ 0.01-0.02/piece. Firstly, the farmers stock the small seed in an area of confined water enclosed by bamboo or netting. There are no improved pond management techniques developed for grow-out crab culture. Farmers follow traditional process without maintaining any specific stocking density or measures to improve growth and survival. In the first half of the year, they stock crablets in ponds for culture for 3-4 months and provide low amounts of feeds on an irregular basis. In the second half, they start fattening crabs in the same ponds. Absence of separate nursery and grow-out ponds increases predation through cannibalism due to large size variation, resulting in lower production. Soft-shell Production Soft-shell crab production is very new in Bangladesh and is being done on a limited scale in Cox’s Bazar and Satkhira regions (lslam et al. 2015). Commercial production has been started by business investors who have recently established about 18-25 farms in the southeast and southwest regions (Fig. 4). Large numbers of floating plastic boxes (about 70,000/ha) are set up in a pond. Boxes are tied to PVC-pipe floats to facilitate checking crabs during culture. A single crab, typically males or immature females or females with under-developed gonads (size 50-140 g), is stocked in each box and fed with locally available fresh fish, mostly small tilapia. Male crabs grow 65 percent faster than females through the molting process. Operators monitor crab boxes continuously at 4-hr intervals to check for molting. Crabs are harvested immediately after molting and moved to clean water to remove dirt and grime, followed by freezing and shipment. About 30-45 days are required to complete each cycle, depending on the quality of stocked crabs, supplied feeds, and overall pond environment. The estimated annual production of soft-shell crab farming is 25-30 t/ha with 50-60 percent survival. The price offered by suppliers/buyers is about US$ 4.96-6.20 for grade A (no defects) and about US$ 2.85-3.10 for grade b (with defects such as lost appendages). Water quality and any chance of disease contamination are properly examined in soft-shell farming. Compared with other crab production systems, soft-shell production requires a large investment, labor, critical attention, large stocking, and a tedious feeding and checking process. Crab Fisheries During the mid-1970s, harvesting from nature was the only source of Bangladeshi mud crab exported to international markets. The mud crab fishery is year-round with a peak season from May to July. The quantity harvested from wild stocks is unknown. There are about 5,000 families in coastal communities involved in crab fishing and different groups are involved with crab picking. A crabber group (single or husband-wife) collects crab daily, traveling short distance in estuaries, tidal rivers, mangrove forest swamps and coastal creeks (Fig. 5). Others are independent and subservient groups consisting of 5-10 members who usually spend about 7-10 days in each drive FIGURE 4. Soft-shell mud crab farm in Shyamnagor, Satkhira, Bangladesh. Photo: Md. Mojibar Rahman. FIGURE 5. Mangrove crab harvesters in Shyamnagor, Satkhira, Bangladesh. Photo: Md. Mojibar Rahman. (CONTINUED ON PAGE 50)
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