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 andbamboo) 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) werejoined 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); mortalityalso 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.Keywords: Mud crab, Pens, Cages, Bamboo, Fito, Cost-Return, Conservation
Highlights
The mud crab (Scylla serrata) is the only species of the genus Scylla in the Indian Ocean
No physical effect was observed on the mangrove tree stands at the end of the culture experiment in the pen and cage culture sites apart from the less than 5% mangrove prop root trimming during construction of the culture facilities
Growth rate and survival of crabs showed no interaction within treatments
Summary
The mud crab (Scylla serrata) is the only species of the genus Scylla in the Indian Ocean. It has both ecological and economic importance to the marine environment and to the coastal fishing villages (Keenan et al, 1998). Mud crabs are sought as quality food for local village consumption and for sale in tourist hotels, where they fetch high prices due to their. The mud crab fishery in the Western Indian Ocean (WIO) region is dependent on artisanal fishermen who use traditional capture methods (hook sticks, pots, traps and seine nets). The demand for mud crabs both from local tourist hotels and, in particular, from the export market is large and is growing rapidly in both Kenya and Tanzania
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