Department of Aquatic Sciences and Fisheries Technology

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    Bivalves Fouling Floating Cages Used in Aquaculture
    (1972) Bwathondi, Philip O. J.; Ngoile, M.
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    Preliminary Investigation on the Rabbitfish, Siganus Canaliculatus in Tanzania
    (Elsevier, 1982) Bwathondi, Philip O. J.
    Preliminary investigation on the culture of Siganus canalicullatus in floating cages in Tanzania coastal water has revealed that the fish has high culture potential in the region. It is euryhaline, inhabiting areas where salinities range from 23‰ to 35.8‰. The fish grows faster on pelletted diets than on ordinary seaweeds. It is estimated that the fish would reach a marketable size of 20 cm fork length in 6 months; hence two crops can be harvested in a year.
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    Physical Processes in the Rufiji Delta and Their Possible Implications on the Mangrove Ecosystem
    (Springer, 1992) Francis, Julius
    The physical processes such as coastal currents, estuarine circulation and monsoon winds prevailing in the Rufiji delta are discussed. The relationship between these processes and the occurrence of long-term trapping of the river discharge and the outflow of waters from the mangrove swamps into the nearshore zone has been observed. The trapped waters in the nearshore zone significantly reduce the mixing between the estuarine and offshore waters, leading to the two waters having distinctive properties. The existence of the trapped waters in the nearshore zone is supported by evidence from a satellite image and aerial photograph and measurements of salinity and suspended sediment concentration. The trapping phenomenon is discussed in the light of its possible implications on the ecology of mangrove ecosystems. Trapping may explain the enhanced growth of the mangrove in the delta compared to other areas. This trapping effect may be providing more time for nutrient retention in the mangrove zone, incorporation of the decomposed leaf litter and fine sediments in the substrate, and settling of fruits and seedlings in the swamps, thereby enhancing the regeneration of the mangrove.
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    Nearshore Fish Resources and Fisheries around Kigoma, Eastern Coast of Lake Tanganyika
    (1992) Ndaro, Simon G. M.
    The fish habitats along an inshore water stretch along the eastern/central coast of Lake Tanganyika are discussed and a quantitative analysis of the species composition, distribution and abundance of the littoral fishes within the area of study is presented. Seventy-one species of fish belonging to 48 genera and to 15 fish families were collected and identified during the study. The majority of species belonged to the Cichlidae family. Intensive beach seining for clupeids is suggested as one of the causes of low fish biomass in the area surveyed. The areas south of Kigoma appeared to contain more fish, with average catch rates of 11.7 kg/haul than those north of Kigoma where average catch rates of 7.6 kg/haul were recorded. Some suggestions for improved management of these resources are given.
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    Anthropogenic Pollution in the Dar es Salaam Harbour Area, Tanzania.
    (Elsevier, 1992-11) Machiwa, John F.
    Man-made pollutants, namely, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), and heavy metals as well as microbial pollution in the sediments of the harbour channel have been evaluated. Petroleum hydrocarbons, PCBs and heavy metals (Fe, Pb, Cu, and Zn) are at elevated levels in the port area used for loading and unloading activities. The concentration of the chemicals decreases further offshore, with the exception of cadmium which, surprisingly, is enriched in the sediments at the ship outer anchorage zone. The concentration-depth profile of the sediment core samples show that in general metals are uniformly distributed with depth in the sediment. The between station variation of Mn, Cr and Ni is strongly influenced by grain size differences. Total and faecal coliform bacteria are few in the port area but are extremely abundant at the fish landing beach and close to the sewer outfall
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    The Status of the Fishery Resource in, the Wetlands of Tanzania
    (1993) Bwathondi, Philip O. J.; Mwamsojo, G. O. J.
    The main types of wetlands in Tanzania are described as an introduction to a coverage of the fisheries of the large lakes, the minor waters, the rivers and the intertidal ecosystems. Fisheries potential is estimated and details of catches for each wetland type are given. Fishing techniques and the future of the fisheries are discussed and recommendations made for future wetlands fishery conservation.
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    Effects of Intensive Seaweed Farming on the Meiobenthos in a Tropical Lagoon
    (Elsevier, 1995) Olafsson, Emil; Johnstone, Ron W.; Ndaro, Simon G. M.
    Open water aquaculture of the seaweed Eucheuma spinosum, imported to Zanzibar from the Philippines in 1989, is presently a large scale operation on the island, with algal farms covering around a 1000 ha of the intertidal area. To assess the effects of the farming on benthic communities both field and laboratory studies were conducted. Two field studies conducted at different times showed that all major meiofaunal taxa were found in significantly lower numbers within the farm area compared with control areas. Multidimensional scaling ordination of nematode species, genera and family abundance data separated samples from farmed and control areas. There was a significant difference in the nematode assemblage structure among areas in pairwise comparisons using ANOSIM. The trophic structure of the nematode assemblage was characterised by a high number of epistrate feeders in all areas ranging from 73 to 96% of total numbers in the samples. To test the hypothesis that toxic substances excreted by the seaweed were responsible for lower abundance inside the farm area, a laboratory experiment was conducted. Eucheuma plants were added to several microcosms and allowed to grow there for 40 days. The results indicated no effects of the seaweed on the density of the major infauna taxa as no significant difference was found among the treatments. It is concluded that other factors such as increased predation by benthic feeding fish and the mechanical disturbance of the sediments may better explain the observed differences in infauna abundance inside and outside the algal culture farms.
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    Small-Scale Variation in Major Meiofaunal Taxa and Sediment Chemistry in Tropical Sediments
    (1995) Ndaro, Simon G. M.; Sjoling, S.; Olafsson, Emil
    Variations in sediment biochemistry and abundance of meiofauna were investigated in three tropical habitats: mangrove forest, intertidal lagoon, and subtidal reef area in eastern Africa. Both the biochemical components of the pore water and the meiofauna varied substantially over small distances in all three habitats. In the mangrove area, the color of the pore water was found to be positively correlated with the major meiofaunal taxa, especially the nematodes. In the coastal lagoon, polychaetes showed negative correlation with particulate organic matter while other groups showed no correlation with any of the chemical components analyzed. In the subtidal reef area no chemical components were found to correlate with the meiofauna. When data from the three habitats are taken together two clear associations emerge. First, grain size shows a highly significant relationship with both total fauna and nematode numbers. Second, there is clear association between the amount of particulate organic carbon and particulate organic nitrogen in the pore water.
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    The effects of size grading and stocking density on growth performance of juvenile abalone
    (Elsevier, 1995-11-15) Mgaya, Yunus D.; Mercera, John P.
    The effects of size grading and stocking density on the growth of juvenile European abalone, Haliotis tuberculata L. (Gastropoda: Haliotidae) were assessed in the hatchery. Animals were held in cages deployed in a flowtray with recirculating seawater maintained at 18 ± 2 °C, and fed ad libitum on the red alga Palmaria palmata (L.) Kuntze. In the grading experiment juvenile abalone were divided into four populations consisting of small (mean ± s.e; initial shell length = 15.3 ± 0.15 mm; n = 35), medium (initial shell length = 19.6 ± 0.16 mm; n = 35), large (initial shell length = 23.8 ± 0.17 mm; n = 35) and an ungraded control group (16.8 ± 0.41 mm; n = 35). Rearing was carried out over a period of 226 days, after which it could be concluded that an advantage in overall growth performance had been gained by grading the animals. There was evidence that growth of small abalone improved in the absence of larger conspecifics. In the stocking density experiment with two size grades and three stocking densities, a decreasing exponential relationship was found between growth (body weight and shell length) and stocking density, with a substantial amount of growth occurring at all densities. Final total biomass for both grades of abalone increased with density. For the smaller grade biomass gain increased as density increased. However, for the larger grade biomass gain declined at higher density. Overall mean survival (± s.e) was 98.3 ± 0.4% and was not influenced by density. It is suggested that the choice of stocking density is essentially a trade-off between maximum growth, optimal biomass gain, and economic considerations which may dictate densities that would result in a net reduction in overall production costs.
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    Flora and Crabs in a Mangrove Forest Partly Distorted by Human Activities, Zanzibar.
    (Elsevier, 1995-12) Machiwa, John F.; Hallberg, Rolf O.
    A preliminary study on flora and fauna in a disturbed mangrove ecosystem is presented. The zonation of mangrove flora in the forest is clearly displayed by two dominant species, Avicennia marina and Sonneratia alba. A. marina forms an almost pure stand at the terrestrial edge of the forest, but the species is ubiquitous in the area. S. alba almost exclusively occupies the marine fringe of the forest.
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    Trichodesmium Has Cells Specialized for Nitrogen Fixation but Lacks Heterocysts
    (Springer Link, 1997) Bergman, Birgitta; Fredriksson, C.; Janson, S.; Carpenter, Edward; Paerl, Hans; Lugomela, Charles
    Two features make research on the marine cyanobacterium Trichodesmium of particular relevance. The first, relates to its common occurrence and important role in a global perspective. Although Trichodesmium is restricted to coastal habitats and open oceans with temperatures above about 18–20°C, it is probably quantitatively one of the most common cyanobacterium in nature. Recent estimates also indicate that it supports the pelagic zone of the oligotrophic oceans with considerable amounts of fixed nitrogen (Carpenter & Romans 1991). Furthermore, Trichodesmium is unique in that it fixes nitrogen aerobically in light, a feature only known from cyanobacteria differentiating heterocysts, a specific cell type for the oxygen sensitive nitrogen-fixing enzyme nitrogenase.
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    The Impact of the Mangrove Crabs Uca Annulipes and Dotilla Fenestrata on Meiobenthos
    (1997) Olafsson, Emil; Ndaro, Simon G. M.
    To assess the effects of 2 mangrove crabs on benthic meiofauna a laboratory experiment was performed in Zanzibar, eastern Africa. The 2 ocypodidae crab species Uca annulipes and Dotilla fenestrata are commonly found at mid to high water levels among Avicennia marina trees. Both genera are borrowers in soft sediments and feed upon drained surface deposits by forming pseudofaecal pellets. They are efficient bioturbers of the uppermost few mm of the sediment and some Uca species may prey directly on meiobenthos. The 2 species were added to microcosms containing sediment with natural meiofauna populations. After 10 d of enclosure, numbers of harpacticoid copepods in the top 1 cm layer were significantly lower in microcosms containing U. annulipes than in control microcosms. Two nematode assemblages were found in the microcosms, one in the surface layer and one deeper down. The crabs did not alter the structure of these assemblages. It appears that the nematodes are quite resilient to the reworking of the sediment surface. We conclude that the ocypodid crabs do not regulate resident nematode assemblages, but may inhibit settlement of colonisers that have not adapted to the intense surface disturbance created by these crabs. Such biological control is most likely to be in those areas where tidal water contains relatively high numbers of migrating meiofauna.
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    The Development of a Scientific Forum in the Western Indian Ocean Region
    (1998) Kyewalyanga, M.; Francis, Julius; Johnstone, Ron W.
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    The Status of the Coral Reefs of Zanzibar: One Example of a Regional Predicament
    (1998) Johnstone, Ron W.; Muhando, Christopher A.; Francis, Julius
    Coral reefs are an important resource base for many coastal communities throughout the Western Indian Ocean region (WIO). With the continued growth of coastal populations and the concomitant increase in the need for marine resources, coral reefs stand at the face of overexploitation in many countries, and are being subjected to widespread degradation due to destructive fishing practices and pollution. Within this setting, the islands of Zanzibar exhibit almost all of the problems seen throughout the WIO, and so serve to exemplify some of the issues involved. Zanzibar has extensive coral reefs, which are actively used as a resource base by an increasing coastal population. At the same time, the expansion of urban areas and the development of coastal tourist facilities means that the coral reefs are coming under increasing pressure to provide even more resources than they have historically been required to deliver. At the same time, they are recipients of increasing levels of pollutants from expanding human populations, and they are subject to a range of physically destructive activities. In general terms, the reefs of Zanzibar are in comparatively good condition although there are clear areas of significant perturbation adjacent to certain urban areas and areas of high visitation. The main anthropogenic threats to the coral reefs of Zanzibar include overexploitation, destructive activities (fishing and anchor damage), and pollution. There are indications that overfishing of key species may be leading to a decline in certain economic species as well as ecological shifts in the benthic communities of some reef areas. As is often the case regionally, the lack of historical data limits attempts to resolve the true impact of some of these factors. In line with perceived local problems, a number of activities have been undertaken in Zanzibar to address specific coral-reef related issues, and these are discussed here in the light of the larger regional setting. Some discussion is also centered around the basic issues that undermine the sustainable management of coral reefs in Zanzibar, and how these problems are being dealt with in other parts of the WIO.
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    Coastal resources utilization and conservation issues in Bagamoyo, Tanzania
    (1998) Semesi, A. K.; Mgaya, Yunus D.; Muruke, M. H. S.; Francis, Julius; Mtolera, Matern; Msumi, G.
    A study was carried out to provide information about the importance of the management of coastal resources in Bagamoyo, Tanzania. The results showed that the coral reefs at Mwamba Kuni and Mshingwi are the main fishing grounds for the artisanal fishermen. Trawlers compete and conflict with artisanal fishermen. The mangroves provide habitats for fish and other animals and are a source of fuelwood, charcoal, fishing stakes, building materials, and traditional medicines. Solar salt production is also an important activity. Although Bagamoyo depends on renewable resources, the harvesting rates of most resources are not known. Habitat destruction and overexploitation of resources have resulted in declining catches. There is unawareness among the resource users of the linkages between the various coastal ecosystems, but they do have vast traditional knowledge about the resources. In this article, we present the crustacean resources, fish, sea cucumbers, mangrove products, coral reefs, tourism, and salt production activities.
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