World Aquaculture September 2018

44 SEP TEMBER 2018 • WORLD AQUACULTURE • WWW.WA S.ORG or markets. Seed crabs are harvested from natural sources of mainly Sundarbans mangrove forests and associated tidal rives, estuaries and canals. The individual size of seed crabs for stocking varies from 40-200 g but 120-150 g is in greatest demand (Fig. 3), generally at premium prices (Shelley and Lovatelli 2011). Farmers typically stock juvenile crabs in floating boxes at the water surface between 0600 and 2200 h, after their arrival from depots. Most farmers use minced tilapia and/or snail meat as feed for production of soft-shell crabs, often feeding at 5-10 percent body weight daily on an as-needed basis. Fresh tilapia are available in coastal areas and are an acceptable source of protein for crabs. Pre-contracted suppliers provide tilapia to soft-shell crab farms at approximately US$0.50/kg (45 BDT/kg). Small farms can purchase fish from local markets at lower prices. The conventional feeding schedule is once every 2-3 days in summer and a maximum of every 5-7 days in winter, with minced fish given while checking for molting. Pond water is exchanged up to 50 percent weekly during high tides. Soft-shell production ponds are also treated with lime during production at about 0.5 kilogram/decimal (1 decimal = 40.5 m 2 ) twice monthly to maintain water quality, stabilize pH and avoid disease outbreaks. After stocking one small crab per individual box, crabs are checked at 4-h intervals to monitor molting status. Laborers typically remain seated on a platform situated in the middle of the pond, accessing a row of containers using a rope under the platform to observe each crab for indications of molting (Fig. 4). Leftover food materials are simultaneously removed and new crabs stocked into boxes as they come available. Regular monitoring for molting is the most labor-intensive activity, leading to the instant harvesting of molted crabs (Tavares et al. 2017). Molted soft-shell crabs are collected from boxes and held in oxygenated freshwater for 45 minutes to clean and flush intestinal residues from the body, and retained in the soft-shell state followed by grading, weighing, chilling, packaging and storage for shipment (Rahman et al. 2017). Each crop cycle of soft-shell crab production requires an average of 25-45 days (Freeman et al. 1987, Shelley and Lovatelli 2011). Production calculations for soft-shell crabs are complicated because harvesting and stocking are ongoing continuous operations with variable rates and somewhat unpredictable timing. Marketing systems and export earnings. Strong overseas markets for Bangladeshi soft-shell crabs have developed in Australia, Thailand, Singapore, Netherlands, Germany, USA and UK. Among these, the USA, UK and Australia import 80 percent of total production. Buyers’ requirements or pre-contract conditions vary by country with regard to processing, freezing, packaging, wrapping, labeling, and shipment. Mean prices offered by buyers range from US$ 10-15/kg. Soft-shell crab markets are not open to all farms; only experienced, larger-scale producers with export licenses are viewed as acceptable by buyers in the international export market for soft- shell crabs. This marketing system excludes many smaller producers from access to the limited number of buyers. Exporting soft-shell crab to foreign markets is relatively new and therefore no data on earnings of foreign currency are available. In 2015, Bangladesh government reported earnings of foreign currency of about US$ 26 million from exporting 12,558 t live hard-shell crabs (FRSS 2017). Potential for areal expansion. Bangladesh has 710 km of coastline, with the world’s largest mangrove forest (the Sunderbans), which is a richly biodiverse aquatic ecosystem (Rahman et al. 2017). Land in the coastal region is 28 percent very suitable, 62 percent moderately suitable and only about 10 percent marginally suitable for crab farming (Salam et al. 2012). There are about 275,509 ha of shrimp and prawn ghers (modified ricefields) in the coastal zone (FRSS 2017). Many of these water bodies are improperly used for aquaculture, as impacted by shrimp farming, leading to the propagation of pathogens and to environmental degradation (Karim and Stellwagen 1998). The intensification and exploration of crab aquaculture for fattening and soft-shell crab production can potentially make more sustainable use of these water resources. Employment generation. Development of commercial aquaculture creates layers of employment opportunities for landless laborers as they become involved in various parts of associated value chains (Belton et al. 2012). In coastal areas, commercial soft-shell crab farms thus create significant employment generation opportunity for vulnerable households, and especially for women (Fig. 5). Soft- shell crab farms are labor-intensive, hiring local men and women on a monthly or daily basis. Soft-shell crab farms presently support approximately 600 employees in coastal Bangladesh, the largest of which has approximately 300 employees (79 percent men and 21 percent women). Medium-sized farms employ more women, with an average of 22 employees, consisting of 60 percent men and 40 percent women (Fig. 6). Smaller production units employed an average of 3-6 workers, and also include family labor in the production system. FIGURE 3. Stockable small-size crabs for soft-shell crab production (Photo: Md. Mojibar Rahman). FIGURE 4. Women monitoring the molting status of crabs in cellular box soft- shell crab farm (Photo: Md. Mojibar Rahman).