This study of the socioeconomic root causes of biodiversity loss in Tanzania focused on the mangrove areas of the three most important deltas in the country, namely Wami River Delta and Ruvu River Delta in Bagamoyo District, and Rufiji River Delta in Rufiji District. These deltas, situated in the Coast Region, constitute the largest wetland areas in Tanzania. They extend from the central to southern Tanzania coastal area.
The study area is influenced by a hot and humid coastal climate with temperatures ranging between 25ºC and 35ºC. Temperatures are highest between December and April. Two monsoon winds, the northeast and southeast monsoons, affect the climate. The rainy season is from March to May, with short intermittent rains between October and December. Annual rainfall exceeds 1,000 mm.
Among the six major ecological zones of Tanzania, the Coast Region falls within the Coastal Forest and Thicket zone (Stuart, et al, 1990; Mwalyosi and Kayera, 1995). The total forest area in the Coast Region is about 2.5 million ha, of which 369,523 ha are protected and the rest are open public forest (United Republic of Tanzania, 1997b). The soils in this ecological zone have poor moisture-holding capacity, which results in poor drainage. The Coastal Forest and Thicket zone has a high rate of endemic species including, for example, the blue dwarf gecko (Lygodactylus williamsi) (Mwalyosi and Kayera, 1995).
The Ruvu Delta is located about 67 km northeast of Dar es Salaam. The river’s main catchment area is the Uluguru Mountains in Morogoro Region. The Wami has its sources in the Kaguru Mountains and flows to the southeast across the Mkata Plains to the Indian Ocean. The Delta is about 90 km from Dar es Salaam. The Rufiji Delta is located about 200 km south of Dar es Salaam. Nine major tributaries form the Rufiji River basin, which extends for about 177,000 km2 and covers roughly 20 percent of Tanzania’s area (Semesi, 1991; Rufiji Basin Development Authority, 1981). There are some 43 islands in the Delta. The entire delta area is generally flat.
The three deltas are rich in biological diversity. Most notable are the mangrove forests, macro-invertebrates, and fish. An inventory carried out in 1989 shows that the mangroves of mainland Tanzania cover about 115,500 ha (Semesi, 1991). The Rufiji Delta alone is about 53,255 ha (40 percent of total). Eight species of mangroves are found in these deltas: Avicennia marina, Bruguiera gymnorrhiza, Heritiera littoralis, Ceriops tagal, Lumnitzera racemosa, Rhizophora mucronata, Sonneratia alba, and Xylocarpus granatum. Mangroves protect the coastline against destructive waves, help in microclimate stabilization, and enhance water quality in coastal streams and estuaries. Also, mangroves retain sediments and nutrients, provide habitat for fish, and supply forest and wildlife resources (Mwalyosi and Kayera, 1995).
The mangrove ecosystems support a variety of life forms including crocodiles, hippopotamuses, monkeys, and many birds, such as kingfishers, herons, egrets, and waders. Many types of fish are also found in these deltas. The most common fish species include Hilsa kelee, Liza macrolepis, Chanos chanos, and Thryssa spp. Crustaceans include Scylla serrata, hermit crabs, and prawns. The Rufiji Delta is an important prawn-fishing ground for Tanzania. Molluscs include Saccostrea cucullata, Terebralia palustris, Cerithidea decollata, and Strombus spp. Insects such as wasps, spiders, mosquitoes, and ants are also abundant in the mangrove forest. Lepidochelys olivacea, a rare turtle species, nests near large river mouths in the south of Tanzania, and both it and other types of turtles visit mangroves. (Mwalyosi and Kayera, 1995)