WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2019 57 5,000/m2 and 2,000/m2. Overall, 650 kg of seed clams were stocked in pens and cultured for one year. The annual growth rate of clams was 14 mm and 48 g. Average production obtained from the pen was 2000 kg (about 18 kg/m2). Meats were separated from shells, washed and sold at $1.50/kg and shell was sold at $50/t. Sales of clam meat and clam shell resulted in revenue of US$383. Thus, in a very short payback period of one year, a benefit to cost ratio of 1.26 was obtained. Clams convert atmospheric carbon to blue carbon and thus acts as a carbon sink. The culture of clams assimilates 10.8 t C/yr and the annual rate of carbon removal is 80 t/ha. Black clam culture in the CRPS also assimilated 0.915 t of carbon with a value of US$0.58/t. Advantages of the CRPS The CRPS has many advantages in the context of a changing climate: • Protection from extreme weather events like floods and heavy wind action. • Suitable for seed raising as well as table fish production. • Resilience to fluctuating water levels in wetlands on account of tides and rainfall. • Better biosecurity compared to normal pen enclosures. • Utilization of natural productivity. • Environmentally viable and cost effective. • Low maintenance cost and a long time before replacement is needed. • Intensive utilization of space and ease of harvest. • Greater production is assured in a limited space with rich food and oxygen supply. • Greater growth is possible as energy is saved towards locomotion and feeding. • Availability of natural food and exchange of materials with the bottom. • Easier stock management and monitoring. (CONTINUED ON PAGE 58) Pen culture experimental site stocked with black clams at Thycattuserry, Vembanad Lake. the main factors affecting clam production in the lake. Clam relaying and rack culture were used to increase production of black clams in Vembanad Lake in the context of a decline in natural clam harvests and reduced income. Successful demonstration of clam culture in multi-trophic pens was first done by CIFRI as part of a stock replenishment program under the National Innovations on Climate Resilience in Agriculture (NICRA) project in Vembanad Lake. The CRPS at Thycattuserry was set up with the cooperation of clam fishers registered under the Thycattuserry Black Clam Industrial Co-operative Society of nearly 1200 active clam fishermen. The CIFRI Kochi Centre provided complete technical support from site selection to clam harvest under its supervision and monitoring. Pens of 114 m2 were installed at sites after studying site compatibility to the culture requirements of the clams and other selected species. The wetland is vulnerable to tidal fluctuations and so the site chosen had requirement of a minimum mean depth of 1 m during the summer season. Pens were made with locally-available low-cost bamboo for the framework. Bamboo poles were installed with a 1-m gap. Walls made of high tensile strength HDPE netting were used to encircle the bamboo structure. The wall height is based on the greatest depth encountered in flooded conditions during the peak monsoon and normally ranged from 1.8 to 2.5 m. The pen was designed to withstand the effects of wind and strong currents during floods. The pen was also constructed to divert wind-borne floating weeds such as water hyacinth from the system. If not dispersed, water hyacinth may sink to the bottom after drying and smother clams. Pen structures were divided into two compartments prior to stocking. Small and large black clams collected from the wild (Paathiramannal) were segregated and stocked at approximately Catch of black clam Villorita cyprinoides and size measurement. Black clam harvested from the pen culture, measuring its production, taking clams for processing (removal of meat) and processed clam meat.
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