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  • Coral reefs and their management in Tanzania

    Wagner, G.M. (Western Indian Ocean Marine Science Association, 2004-12-30)
    Western Indian Ocean Journal of marine Science
    Coral reefs are very important in Tanzania, both ecologically and socio-economically, as major fishing grounds and tourist attractions. Numerous fringing and patch reefs are located along about two-thirds of Tanzania’s coastline. These reefs have been partially to severely degraded by human (primarily destructive fishing practices) and natural (particularly coral bleaching) causes. These immediate human causes have been brought about by various socioeconomic root causes, particularly poverty and lack of proper management. After decades of human and natural impacts there has been only limited reef recovery. This paper presents a region-by-region analysis of trends in the condition of coral reefs in Tanzania in relation to the causes of damage. While earlier approaches to management were aimed at non-use of coral reefs in marine protected areas (seldom achieved), recent approaches have aimed at integrated coastal management (ICM) (whether in programs or conservation areas), where zonation into core protected areas and multiple-use areas is based on participatory decision-making involving fishing communities and other stakeholders. Some management initiatives also involve communities in reef monitoring, restoration and ecotourism. This paper examines the management approaches and strategies implemented by various ICM programs, conservation areas and marine parks in Tanzania. It also provides recommendations for further research and coral reef management strategies.
  • Absolute migration and the evolution of the Rodriguez Triple Junction since 75 Ma

    Masalu, D.C.P. (2002)
    Tanzania Journal of Science
    The Rodriguez Triple Junction (RTJ) is a junction connecting three mid-ocean ridges in the Indian Ocean: the Southwest Indian Ridge (SWIR), the Central Indian Ridge (CIR) and the Southeast Indian Ridge (SEIR). The evolution of the RTJ has been studied extensively for the past 10 Ma and the triple junction is believed to be largely a ridge-ridge-ridge (RRR) triple junction. However, due to the scarcity of data its configuration prior to that period is poorly understood. The migration of the RTJ in the hotspot reference frame, for the past 75 million years has been mapped, by reconstructing its traces on the three plates (African, Antarctic and Indian) to their former positions. The results show that the RTJ has migrated northeasterly at velocities varying from 10cm/yr at 70 Ma to 2.6cm/yr at 43 Ma and thereafter 3.6–3.8cm/yr, in a fairly straight-line trajectory, suggesting a stable configuration of the RTJ since its formation. Because the RRR triple junction is the most stable configuration that is possible, it is suggested that the configuration of the RTJ has been largely RRR triple junction since its formation.
  • Mobility and immobility of mid-ocean ridges and their implications to mantle dynamics

    Masalu, D.C.P. (2002)
    Tanzanian Journal of Science
    In the past two decades, the mobility of mid-ocean ridges relative to the mantle (absolute migration) has been correlated with major observable features, such as spreading asymmetry and asymmetry in the abundance of seamounts. The mobility of mid-ocean ridges is also thought to be an important factor that influences the diversity of ridge-crest basalts. However, this mobility has not yet been defined and mapped. The absolute migration of global mid-ocean ridges since 85 Ma has been computed and mapped. Global mid-ocean ridges have migrated extensively at varying velocities during that period. Presently, the fast-migrating ridges are the Pacific- Antarctic, Central Indian Ridge, Southeast Indian Ridge, Juan de Fuca, Pacific-Nazca, Antarctic-Nazca, and the Australia-Antarctic ridges, migrating at velocities of between 3.3 and 5.5 cm/yr. The slow-migrating ridges are the Mid-Atlantic and the Southwest Indian ridges, migrating at velocities between 0.3 and 2.0 cm/yr. Comparison of these results with mantle tomography results show that the slow-migrating ridges have deeper depth of origin than the fast-migrating ones, suggesting a correlation between the absolute migration velocity and the depth of origin of ridges. Furthermore, the Southwest Indian ridge appears to be tapping the same portion of mantle as did the Central Indian ridge. These results have important thermo-chemical implications, such as variations in the extent of melting and mineralogical composition of the mantle beneath different ridges, which may influence mantle dynamics.
  • Shore Morphology and Sediment Characteristics South of Pangani River, Coastal Tanzania

    Shaghude, Y.W. (2004)
    The shore morphology and nearshore sediments between the Pangani and Kipumbwi rivers were investigated to describe the shore and the reef platform sediments characteristics and also to update information on recent shoreline changes along the Tanzania mainland coast. The information gathered during this study comes from field observations, sediment sampling of the area and interviews with Pangani residents. The investigated area is a patch reef coast with narrow or no beaches and fossil reef terrace islands offshore, Pangani bay and estuary are among the most prominent shore features. Historical information indicates that, both the bay, and the estuary have undergone significant changes during the last 60 years. While the growth of the estuary has mainly been influenced by the reduced fresh water discharges, the bay has been mainly influenced by shore erosion induced by the high wave activity. The distribution of sediments on the sea bottom is mainly controlled by bathymetry, with sand (medium to coarse) dominating water depths less than 10 m and silt dominating depth greater than 15 m. Sediments in water between 10 and 15 m depth are dominated by fine sand/silt. The carbonate production in the investigated area is limited by the high influx of siliciclastic sediments from the Pangani, Kipumbwi and Ushongo Mabaoni depo-centres. While previous studies attribute the disappearance of Maziwi island to sea level rise, the present study considers the anthropogenic influence to be the major causative factor. Sea level is also considered to be one of the potential threats to the preservation of small islands such as the Maziwi, However, the present study believes that if indeed the vegetation on the island has been cleared as is reported, this action has hastened its disappearance.
  • Land Based Activities and Sources of Pollution to the Marine, Coastal and Associated Fresh Water Ecosystems in the Western Indian Ocean Region

    Francis, J.; Mmochi, A.J. (2003)
    The lack of infrastructure and treatment facilities for the large quantities of domestic sewage generated by expanding coastal urban populations, and an increasing number of visiting tourists, represents the greatest threat to public health, coastal habitats and economic development in each state of the region. Other priorities requiring action include the effects of siltation related to agricultural activity and the dumping of solid domestic waste in the coastal areas leading to the degradation of coastal habitats, with implications for fish stocks and catches. Furthermore, laws and policies regardinng waste disposal and quality of effluents need to be enacted and reinforced Although eutrophication and algal blooms associated with agricultural, industrial or domestic sewage pollution have been identified as a threat to coastal habitats, further scientific research is required to link the causes and effects. Monitoring programmes need to be initiated in the region in order to mitigate pollution. Agriculture is the backbone of the economy of most countries in the region. In 1982, 90% of the population in the region depended on agriculture. With the exception of Mauritius, the physical effects of siltation resulting from agricultural activities are currently of greater concern throughout the region than agrochemical pollution. There is insufficient evidence to indicate whether pesticide pollution in the more intensively farmed coastal areas of the region poses a significant threat to potable water supplies, or to coastal habitats receiving elevated nutrients loads in agricultural run-off. The trend in increased use of both fertilisers and pesticides in intensive agricultural production is likely to lead to elevated concentrations of chemicals in agricultural runoff and ground waters. Overall, industrial development in the region remains relatively low. Industrial activities are focused at the ports and harbours of both the mainland and island states. The number and type of manufacturing industries have changed considerably since 1982. Few industries in the region have waste treatment plants and/or recycling facilities. Many industries empty effluents directly into creeks and rivers leading to the sea or directly to coastal waters. Furthermore, toxic wastes have recently started appearing among wastes disposed. There is a direct relationship between population growth and waste generation. In the case of most large urban centres the solid waste and sewerage facilities have remained the same while the population has increased leading to decline in percentage population served by the facilities. Only a small proportion of dwellings throughout many of the large urban centres of the mainland states are connected to a sewage system. Even then the sewage collected is often pumped directly into coastal waters without any treatment. Rapid urban population growth in the coastal towns have lead to rapid changes in land use patterns. Natural ecosystems are being disturbed or replaced by agricultural crops. The large coastal population is also putting pressure on the marine and coastal resources. Lack of infrastructure and treatment facilities for the large quantities of domestic sewage generated by expanding coastal urban populations, and an increasing number of visiting tourists, represent a great threat to public health, coastal habitats and economic development in the region. Although monitoring data are not available, there is a perceived link between domestic sewage and the occurrence of water borne diseases in most of the coastal townships in the region. There is an urgent need for monitoring of microbial contamination of ground waters in coastal areas of all states of the region. This paper provides an inventory of land-based activities and sources of marine pollution to the marine coastal and associated fresh water environment. It further oversees future developments and suggests priorities for action to mitigate the problems.
  • Sharing experinces on mariculture development with stakeholders

    Jiddawi, N.S.; Mmochi, A.J. (Zanzibar: WIOMSA, 2004)
    WIOMSA News Brief
  • Remote Sensing for Studying Nearshore Bottom Morphology and Shoreline Changes

    Shaghude, Y.W. (Maputo : Direcção Nacional de Geologia, 2004)
    Boletim Direcção Nacional de Geologia, Moćambique
    The major objective of the present study is to demonstrate how remote sensing approach can be used for studying nearshore bottom morphology and shoreline changes in coastal Tanzania. Two study sites were used. In the first site, remote sensing satellite Landsat Thematic Mapper data was evaluated against known water depths from conventional echo sounding measurement taken on the eastern side of the channel. The correlation between the remote sensing data and the echo sounding mesurement was rather satisfactory, suggesting that the approach can roughly be used to investigate sea bottom morphology in the nearshore areas. In the second study site, remote sensing satellite data from Landsat Thematic Mapper and Enhanced Thematic Mapper were used to investigate shoreline changes along the western side of the channel. The results of the study show that the delta and the shoreline north of the delta is currently accreting, where significant accretion has occurred between 1986 and 2000 than before 1986.
  • The Assessment of Water Quality and Pollution in Tanzania

    Mohammed, S.M. (2000)
    The coastal area of Tanzania (Fig. 1) encompasses a number of habitats that include coral reefs, mangroves, seagrass beds, sand banks, wetlands and beaches, among others. In addition to being essential linkages in the overall functioning of the coastal area, these coastal habitats support various resources both living and non-living. In addition, for generations the coastal area has provided life support to coastal communities where such activities as fisheries and related activities have played an important role in the social and economic development of local communities. In recent years, coastal tourism and mariculture have immerged as being potentially among most important economic activities nationally. The well being of these habitats and resources and the various activities taking place within or near coastal waters depend, to a large extent, on good water quality. However, expanding coastal populations and emerging industrial a
  • Sediment Distribution and Composition on the Shallow Water Carbonate Basin of the Zanzibar Channel

    Shaghude, Y.W. (Dar es Salaam: University of Dar es Salaam, Faculty of Science, 2003)
    Tanzania Journal of Science
    The sediments of the shallow water carbonate basin of the Zanzibar channel were investigated to describe their general characteristics in terms of composition and grain size distribution. The surface sediment composition was dominated by carbonate sands (with CaCO3 > 30%), except in the area adjacent to the mainland coastline and a thin lobe which projects from Ruvu River to the middle of the channel. The mean grain size distribution closely resembled that of the carbonate content, where the Tidally Dominated Reef Platform Sediments (TDRPS) located east of the Zanzibar channel were characterised by medium to coarse sands and the siliciclastic sediments adjacent to the mainland are characterised by fine sand. The TDRPS were the most poorly sorted sediments with sorting values between 1.2 and 1.6 phi. The present study highlights the major differences between the eastern and western side of the channel. The sediments on the eastern side of the channel, which were predominantly biogenic, are characterized by grain size frequency curves without any prominent mode. The sediments on the western side of the channel were composed of both biogenic and terrigenous material. The grain size frequency curves of these sediments have a fine mode and usually a coarse tail. 1
  • The Incidental Catch of Dolphins in Gillnet Fisheries in Zanzibar, Tanzania

    Amir, O.A.; Berggren, P.; Jiddawi, N.S. (Western Indian Ocean Marine Science Association (WIOMSA), 2002)
    Western Indian Ocean J. Marine Science
    The level of incidental catches of dolphins in artisanal gillnet fisheries was investigated in a questionnaire survey of 101 gillnet vessel operators from 10 villages in Unguja island of Zanzibar, representing half of all the gillnet fishing fleet in 1999. A total of 96 dolphins were reported to have been incidentally caught between 1995 and 1999; 43 Indo-Pacific bottlenose dolphins (Tursiops aduncus), 29 spinner dolphins (Stenella longirostris), 5 lndo-Pacific humpback dolphins (Sousa chinensis) and 19 unidentified dolphins. Most of these incidental catches (46) were reported in 1999. We extrapolate that 93 animals may have been incidentally caught by the entire fishing fleet (201 vessels) during 1999. This estimate represents a serious cause for concern, suggesting that the incidental capture of dolphins in Zanzibar's artisanal gillnet fisheries may be high enough as to have a significant negative impact on local populations. Further studies to accurately estimate the total bycatch, as well as the abundance of dolphin populations in the area are essential to assessing the biological significance of these incidental catches. However, management efforts should be implemented immediately to reduce the number of dolphins killed in these fisheries.
  • Biogenic Assemblage and Hydrodynamic Settings of the Tidally Dominated Reef Platform Sediments of the Zanzibar Channel

    Shaghude, Y.W.; Wannas, K.O.; Mahongo, S.B. (Western Indian Ocean Marine Science Association (WIOMSA), 2002)
    Western Indian Ocean J. Marine Science
    The biogenic assemblage and hydrodynamic settings of the tidally dominated reef platform sediments (TDRPS) east of the Zanzibar channel were investigated in order to characterise the carbonate sediments. Benthic foraminifera were found to be the most important group both in terms of average abundance (> 60 % by weight) and also in terms of spatial distribution with ommon occurrence in all sediments samples. Pelecypods with an average abundance of 8 % were slightly less widely distributed. The remaining groups occurred at lower average abundance and less frequently in the sediments. Current measurements indicated that the maximum current speed is higher during spring than during neap tides. The direction is phase-dependent with flood tidal current flowing from the northern and southern tips of the island towards Zanzibar town. The ebb current flows in the opposite direction. The geomorphological setting of the carbonate platforms together with the present investigation of the currents and biogenic assemblage of the clastic sediments permits us to subdivide the reef platform area in the Zanzibar Channel into two sub-provinces: the northern and the southern. The northern sub-province contains significantly higher proportion of lithogenic particles. Pelecypods, gastropod and ostracods than the southern sub-province. Some samples from the southern sub-province had significantly higher proportion of corals, than those from northern sub-province.
  • Water, Salt and Stoichiometrically linked nutrient budget for Chwaka Bay, Tanzania

    Ngusaru, A.S.; Mohammed, M.S. (Western Indian Ocean Marine Science Association (WIOMSA), 2002)
    Western Indian Ocean J. Marine Science
    The water and salt balance at Chwaka Bay in Zanzibar, Tanzania suggests that in order to balance the inflow and outflow of water, there must be a net flux of water from the bay to the open ocean during both the dry and wet seasons. The corresponding salt residual fluxes indicate advective salt export. However, exchange between the bay water with the open ocean replaces this exported salt via mixing. The freshwater residence times at Chwaka Bay are 24 days for dry and 37 days for wet season. The budgets for non-conservative materials indicate a net dissolved inorganic phosphorous (DIP) and dissolved inorganic nitrogen (DIN) flux from the bay to the ocean during wet season. The calculated DIPsyst and DINsyst suggest that the bay acts as a DIP and DIN source during the wet season. Stoichiometry calculations suggest that (p-r) is negative, indicating that Chwaka Bay is net heterotrophic during wet season. The inner bay seems to have net denitrification, but the outer bay seems to be fixing nitrogen at a slower rate. However, the entire bay appears to balance nitrogen fixing and denitrification.
  • Effects of Fish Culture on Water Quality of an Integrated Mariculture Pond System.

    Mmochi, A.J.; Dubi, A.M.; Mamboya, F.A.; Mwandya, A.W. (Western Indian Ocean Marine Science Association (WIOMSA), 2002)
    Western Indian Ocean J. Marine Science
    Six mariculture ponds were flooded with seawater since 1996. During this time the ponds were stocked with finfish (milkfish and rabbitfish), which were fed on locally produced fish feed. Some water quality parameters such as temperature, salinity and oxygen saturation were measured twice a day for three years (1998-2000), while nutrient concentrations were measured weekly for one year. Both nutrient concentration and oxygen saturation levels have shown a trend indicating eutrophication. Oxygen concentration changed from an average of 7.16 mg/l in October 1998 to 2.2 mg/l in March 2000 with a negative linear regression of 0.69 during the morning hours. From August 1998 to April 1999 dissolved inorganic ammonia concentration increased by 9 µg-at NIl, from 8.91 to 18.02 with a positive linear regression of 0.79. During this period soluble reactive phosphorus increased by 3.55 µg-at PII from 4.36 to 7.91 with a positive linear regression of 0.75. In this paper the rate of eutrophication and the limit at which the ponds have to be dried/limed before restocking are discussed.
  • Coral Reef Benthos and Fisheries in Tanzania Before and After the 1998 Bleaching and Mortality Event

    Muhando, C.A.; Mohammed, M.S. (Western Indian Ocean Marine Science Association (WIOMSA), 2002)
    Western Indian Ocean J. Marine Science
    Surveys conducted in the 1980s and early 1990s indicated that coral reefs in Tanzania were being degraded by overexploitation and destructive resource harvesting practices, particularly dynamite fishing and the use of dragnets, with concomitant reduction in fish abundance. Despite reduction in dynamite fishing on most parts of the Tanzania coast, recent coral reef surveys (1999 and 2000) have indicated that live coral cover and the health of reef corals were further degraded by the 1998 coral bleaching event. The extent of coral mortality differed between areas and species. Although the relative contribution of some taxa such as acroporids and pocilloporids decreased on most reefs surveyed, there was no evidence of species extinction. Despite extensive coral mortality, there has been little evidence to suggest decline of reef fish abundance of commercial and artisanal fish catches. In many areas the dead reef structure has remained largely intact three years following the bleaching event. Coral recovery through growth of the surviving colonies and new coral settlement has been observed in all sites, but at different levels. The surviving Montipora, Echinopora and some Fungia were recovering faster than others in some sites. Studies in Mafia, Bagamoyo, Dar es Salaam and Tanga showed that pocilloporids had the highest number of recruits. Faster recovery will, however, depend on the level of natural and human disturbances in the near future. Appropriate reef management strategies, such as enforcement of existing regulations and establishment of more marine protected areas would help to prevent further coral reef degradation. Initiation of coral reef restoration programmes may also enhance the recovery process. Capacity building for coral monitoring/research and appropriate infrastructural support for coral reef ecosystem conservation would also bring noticeable improvement.
  • Estimating fishery statistics in the artisanal fishery of Zanzibar, Tanzania: How big a sample size is required?

    Jiddawi, N.S.; Stanley, R.D.; Kronlund, A.R. (2002)
    Western Indian Ocean J. Marine Science
    We examined the sampling effort required to estimate annual fishery landing statistics from the artisanal fishery. Using the observed variability among landing days in two villages in Zanzibar, Tanzania, we are able to present the relationship between predicted precision and sampling effort and take advantage of the strong correlation between lunar day and landings to demonstrate a potential gain in sampling efficiency of 30 % from stratification. The observed data are then used to simulate a 'virtual' year of landings for the two villages and demonstrate how the simulated year of observations can be used to simulate and assess various sampling strategies. In addition, it provides a heuristic tool for demonstrating the likelihood of how much anyone sampled data set may differ from a 'known' value. Finally, we discuss how studies of specific individual landings sites (index sites) could be employed to provide better harvest information for assessing and managing not only the artisanal fisheries of Zanzibar but also small scale fisheries elsewhere.
  • Effect of Frequency of Fertilisation on Abundance of Rotifers and Protozoa in Flooded Ponds and Simulation Tanks

    Kyewalyanga, M.S.; Mwandya, A.W. (2002)
    Western Indian Ocean J. Marine Science
    Experiments to assess a suitable rate of fertilisation of earthen ponds for production of rotifers and protozoa were conducted in April 2000. Production of rotifers and protozoa (hereinafter collectively referred to as rotifers) was stimulated by flooding the ponds using seawater and rainfall. In the simulations, seawater diluted to 20 ppt salinity activated initial production. In all systems, the fertiliser concentration was approximately 1 ml of chicken manure to 2 litres of seawater. Three different rates of fertilisation were tested. The results clearly showed that the higher the frequency of addition of manure, the higher the production of rotifers per ml. Fertilised ponds had maximum averages of between 64 and 76 rotifers/ml as compared to a maximum average of 36 rotifers/ml in control ponds. High number of rotifers was accompanied by a decrease in the concentration of ammonia-N. The average maximum for the daily fertilisation treatment reached 95 rotifers/ml; treatments with every two days and every three days had maximum averages of 68 and 41 rotifers/ml respectively. Observation on nutrient concentrations revealed that, generally, the concentration of nitrogenous nutrients was inversely correlated with the concentration of rotifers per ml.Thus, although fertilisation of earthen ponds is paramount for the production of rotifers, the rate at which fertilisation is done could determine the quantity produced per ml of water.