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- Moksnes, Per-Olav, 1965, et al.
(författare)
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Feasibility of extensive, small-scale mud crab (Scylla serrata) farming in East Africa
- 2016
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Ingår i: Western Indian Ocean journal of marine science. - 0856-860X. ; 14:1-2, s. 23-38
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
- Moksnes, Per-Olav, 1965, et al.
(författare)
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Stepwise function of natural growth for Scylla serrata in East Africa : a valuable tool for assessing growth of mud crabs in aquaculture
- 2015
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Ingår i: Aquaculture Research. - : Hindawi Limited. - 1355-557X .- 1365-2109. ; 46:12, s. 2938-2953
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Tidskriftsartikel (refereegranskat)abstract
- Predicting growth is critical in aquaculture, but models of growth are largely missing for mud crab species. Here, we present the first model of natural growth in juvenile and adult mud crabs Scylla serrata from East Africa using a stepwise growth function based on data on intermoult periods and growth at moult from field mark-recapture, pond and laboratory studies. The results showed a sigmoid growth pattern in carapace width and suggest that S.serrata in East Africa will reach 300g and sexual maturity similar to 9.9months after settlement, and a commercial size of 500g after 12.4months. Analyses of the literature identified several issues with the common praxis to compare standard growth measures between aquaculture studies with different initial size or growing periods. Using the new growth function to estimate the proportional difference between modelled and obtained growth as an alternative method, we show that growth rates of S.serrata cultured in cage systems, which are dominant in East Africa, was <40% of the estimated natural growth and growth obtained in pond systems. The analysis also indicated that growth rates of S.serrata in Southeast Asia was over 50% higher compared with similar culture systems in East Africa, and that different species of mud crabs had large differences in growth rates. This study shows that growth in the present mud crab aquaculture systems in East Africa is below their expected potential. Further work is needed to identify the factors behind this observation.
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