Fieldwork in Madagascar required.
The mud crab Scylla serrata is the only species of Scylla found in the Western Indian Ocean. A portunid crab, this species is exploited by local traditional fishermen both for subsistence, consumption in local tourist establishments, supply to regional and national markets, and commercial export (Raharison 2010, Bautil et al 1991).
Crabs are collected by fishers using a range of fishing methods including hand-collection, nets and hand-scoops (Kipao) (Gough et al 2009 and Rasolofo 2007). Demand for mud crab, particularly from commercial export markets is growing, and due to the largely unregulated nature of fisheries in Madagascar anecdotal evidence from other areas in Madagascar as well as traditional knowledge from local fishermen suggests that crab stocks are being quickly depleted by overfishing. The Malagasy national law indicates a collection size minimum of just 10cm which, when compared to other studies of the same genus and species (Hill 1975, Tongdee 2001, Overton and Macintosh 2002, Jayamanna and Jinadasa 1993, and Robertson and Kruger 1994) is estimated to be either at or below the minimum size at maturity for the species (10 to 12cm for female crabs and 12 to 14cm for males). Although specific studies have not been conducted on crabs of the Menabe region, Western Madagascar, this national law could undermine the sustainability of the crab fishery if it remains unchanged.
The crab fishery of Belo sur Mer is one of the largest export markets from the region. The primary collector of Scylla serrata, a fisheries collection company operating out of Morondava, is licensed to export 50 tonnes of Scylla serrata per annum, however actual export is considered to be far below this level due to the degradation of the fishery.
This research project aims to undertake an in-depth assessment of the crab populations of the area, at a critical time in the development of fisheries management for this species. Specifically, this research will assess the following criteria that will be used as guidance for both local fisheries management and national legislation;
1. Growth rates of crab (determined through mark-recapture assessments)
2. Size at Maturity (through mark-recapture or fisheries landing assessments)
3. Seasonality of mating and spawning behaviours (TEK/mark-recapture/fisheries landings)
4. Effects of habitat degradation on crab population (fisheries landings/habitat assessments/visual assessments)
5. Effects of management strategies on populations such as temporary/permanent reserves (fisheries landings)
Bautil, B. R., Ramantoniaina, J., and Carrara, G., 1991. Etude Préliminaire de la Ressource en Crabe des Mangroves (Scylla serrata) du Nord-Ouest de Madagascar. Food and Agriculture Organisation of the United Nations, 1991. 15 pp plus 18 tables, 29 figures and 12 Annexes.
Gough, C., Thomas, T., Humber, F., Harris, A., Cripps, G., and Peabody, S. (2009) Vezo Fishing: An Introduction to the Methods Used by Fishers in Andavadoaka Southwest Madagascar. Blue Ventures Conservation Report.
Jayamanna, S.C. and J. Jinadasa 1993. Size maturity and spawning periodicity of the mud crab Scylla serrata (Forskal) in Negombo estuary. Journal of Natural Science Council- Sri Lanka 21:141-152.
Overton, J.L., and Macintosh, D.J. (2002) Estimated size at sexual maturity for female mud crabs (Genus Scylla) from two sympatric species within BanDon Bay, Thailand. Journal of Crustacean Biology 22(4): 790-797
Raharison, D. A. (2010) Travaux d'appui a l'etablissement de l'aire protegee marine et cotiere du sud Nenabe: Etude d'Impacts Sociaux. KilyBe
Rasolofo, M.V. (1997) Use of mangroves by traditional fishermen in Madagascar. Mangroves and Salt Marshes 1: 243-253
Robertson, W.D. and A. Kruger. 1994. Size at maturity, mating and spawning in the portunid crab Scylla serrata (Forskal) in Natal, South Africa. Estuarine, Coastal Shelf Science 39:185-200.
Tongdee, N. (2001). Size distribution, sex ratio and size at maturity of mud crabs (Scylla spp.) in Ranong Province, Thailand. Asian Fish. Sci. 14: 113-120