Mud Crab (Scylla serrata) Culture: Understanding the Technology in a Silvofisheries Perspective

Abstract

A study was conducted in Mtwapa creek on the north coast Kenya, during 2005-2007 to evaluate the viability of pens and drive-in cages for mud crab (S. serrata) culture as a mangrove management strategy and alternative source of income for local communities. Other objectives were to assess the effectiveness of drive-in cage construction materials (fito and bamboo) in improving mud crab culture and influences return on investment. The applicability of morphomentric equations in estimating growth was also tested. Four replicate pens (6 m x 2 m) were stocked with 2 crabs/m2 while individual drive-in cages (30 cm x 30 cm x 30 cm) were joined to form ten in one group (1 replicate) and a total of four replicates used. Uniform feeding was applied for all crabs in pens and drive-in cages using a mixture of fish offal and gastropod meat once a day at 10% body weight. Specific growth rate and survival of mud crabs were evaluated together with the cost of investment for the three months culture period. Drive-in cages recorded a significantly better survival and growth rate (53.2 ± 12.78%; 1.25 ± 0.42 g/day) compared to pens (31.25 ± 2.95%; 0.68 ± 0.24 g/day) p < 0.05 while no significant difference was observed between drive-in cages made of different materials (fito and bamboo). A link between growth rate and size of crab was observed, where growth rate decreased with increasing weight. Moulting associated factors contributed highly (45%) to the total mud crab mortality recorded (p < 0.05); mortality also had a strong positive relationship with moulting (R2 = 0.79, p > 0.05). Strong relationships existed in morphomentric equations between carapace length and weight (W = 0.0006L2.9941; R2 = 0.86, p > 0.05). The construction costs for pens were three times more than those for a similar number of drive-in cages. Cost-return analysis on a per year basis/50 crabs showed that the use of either bamboo or fito as cage construction material was economically viable with a return on capital investment of 122.3 -181.7%. Therefore the integration of mud crab culture in mangrove forest is feasible in Kenya.