IMS, Zanzibar, Tanzania

Zanzibar is an independent enclave in the Republic of Tanzania. It is separated from the mainland by the Zanzibar channel which is about 60 km at its narrowest. It consists of two major islands; Unguja (146,400 ha), and Pemba (86400 ha) and some smaller islands ¾ Fundo, Kojani, Panza and Tumbatu, and Mnemba. The total land area of Zanzibar is thus 264,180 ha., of which approximately 6% is under mangrove vegetation. Pemba has the largest mangrove area, covering about 14 % of its land surface area, while the mangrove forest in Unguja covers about 5 % of the total land area (Amour 1993).

The islands of Zanzibar are small, flat, coral islands without large rivers. The tides rise to about 5 metres at the spring and to about 3 metres at the neaps, giving a tidal range of between 3-4 m. Accretion occurs by the deposition of silt from land erosion and by the deposition of sand by sea and tidal currents (Griffith 1949). The deposition of sand by sea and tidal currents has been observed along the north-eastern part of Mnemba Island, on the north east coast of Unguja island (per.obs.) Pemba island, though relatively smaller than Unguja island has, nevertheless, the largest mangrove vegetated area, most of which is found on the western side of the island, where there are numerous protected inlets which form suitable sites for mangrove growth. Pemba island is also more hilly, with deep soils. Erosion, often caused by careless cultivation on the hill sides, leads to the deposition of muddy soils in the numerous inlets providing suitable habitats for mangrove vegetation. Unguja island on the other hand has a rocky substrate (often referred to as the coral rag area) especially on the east coast. Most of the fertile land is found on the western side of the island. It is also on this part of this island that one finds areas that are suitable for mangrove growth. Thus mangrove swamps occur at; Maruhubi (Kinazini); Tumbatu; Nyamanzi; Makoba Bay; Chukwani , Pete, Unguja – Ukuu, Uzi, Fumba and Kisakasaka, all on the west coast. Most of the east coast, except at Chwaka Bay, is a high energy area without protected beaches and is consequently unsuitable for mangrove swamp formation. Chwaka Bay with several creeks dissecting the dead coral rock basement, typical of the substrate, forms a unique mangrove stand on the east coast of Unguja Island.

Apparently there is no river draining into the bay, but there is an underground seepage of water from the adjoining Jozani forest and Cheju catchment areas, because fresh water wells and springs are common on the landward edge and cliffs, respectively, of the Chwaka mangrove forest (Shunula et al.1999).

The mangrove vegetation occupies a key position in the livelihood of the peoples of Zanzibar of whom between 10-30% of the total population are involved in fishing and or the collection of shellfishes such as crabs and various types of molluscs as well as charcoal extraction. Ngoile and Shunula (1992) reported between 80-90% of the fishing effort to be concentrated in waters close to mangrove vegetated areas. Recent efforts to educate the local community through research, videos shows, seminars and workshops on the linkages between mangrove vegetation and the availability of especially fish has begun to yield fruits in that several local communities are already beginning to protect and plan better use for their mangrove resources. This is a positive step towards the rational utilization of this resource.

This paper discusses among other things what has happened which has helped to change the perception of the local community towards the mangrove resources.