Feasibility of extensive, small-scale mud crab (Scylla serrata) farming in East Africa.

Small-scale farming of mud crabs (Scylla serrata) has been suggested as a low investment alternative for generating incomes to resource-poor coastal communities in East Africa. However, it is unclear if the present culture methods are profitable and ecologically sustainable. Here we assess the two dominant culture methods, extensive ‘crab-fattening’ in cages (cage culture) and grow-out farming of small juveniles in ponds (pond culture) using economic and ecological analyses in Kenya and Tanzania. Cost-revenue analyses of cage culture showed negative results at all scales in both countries. High labor costs and poor survival and growth make cage culture an unprofitable and unsustainable livelihood in its present form. Pond culture showed a positive return at prices above $US 3.4 kg-1, which is achievable in Kenya and Mozambique, but not in Tanzania. Analyses also showed that larger ponds and selling crabs at a smaller size improved profitability. However, the availability of seed-crabs and local feed sources limit the size of sustainable crab farms in a coastal community to approximately 500 commercial crabs per year. Before crab farming in ponds can become a profitable alternative income in East Africa, survival rates need to be improved, market conditions and profits to local crab farmers enhanced, and potential negative impacts on mangroves evaluated.