Browsing by Author "Mbabazi, Dismas"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Coupled human and natural system dynamics as key to the sustainability of Lake Victoria’s ecosystem services
    (Ecology and Society, 2014) Andrea, S. Downing; Egbert, H. van Nes; John, S. Balirwa; Joost, Beuving; Bwathondi, P.O.J.; Lauren, J. Chapman; Ilse, J. M. Cornelissen; Iain, G. Cowx; Kees, P. C. Goudswaard; Robert, E. Hecky; Jan, H. Janse; Annette, B. G. Janssen; Les, Kaufman; Mary, A. Kishe-Machumu; Jeppe, Kolding; Willem, Ligtvoet; Mbabazi, Dismas; Modesta, Medard; Mkumbo, Oliva C.; Enock, Mlaponi; Munyaho, Antony T.; Nagelkerke, Leopold A. J.; Ogutu-Ohwayo, Richard
    East Africa’s Lake Victoria provides resources and services to millions of people on the lake’s shores and abroad. In particular, the lake’s fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria’s system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake’s social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks’ vulnerability to exploitation but reduce society’s vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales.
  • Thumbnail Image
    Item
    The responses of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) in Lake Wamala (Uganda) to changing climatic conditions
    (Lakes & Reservoirs: Research & Management, 2015) Vianny, Natugonza; Ogutu-Ohwayo, Richard; Efitre, Jackson; Muyodi, Fredrick; Mbabazi, Dismas; Olokotum, Mark; Musinguzi, Laban; Naigaga, Shamim; Namboowa, Sharon
    Changes in the catches of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), in Lake Wamala (Uganda) have been observed since its introduction. The factors contributing to these changes, however, are not well understood. This study examined changes in species composition, size structure, size at first maturity, length–weight relationship and condition factor of Nile tilapia in Lake Wamala, in relation to changes in temperature, rainfall and lake depth, to provide a better understanding of the possible role of changing climatic conditions. There was an increase in the minimum, maximum and average temperatures since 1980, but only the minimum (0.021 °C year 1) and average temperatures (0.018 °C year 1) exhibited a significant trend (P < 0.05). Rainfall increased by 8.25 mm year 1 since 1950 and accounted for 79.5% of the water input into the lake during the period 2011–2013, while evaporation accounted for 86.2% of the water loss from the lake. The lake depth was above 4 m during the years when the rainfall exceeded the average of 1180 mm, except after 2000. The contribution of Nile tilapia to total fish catch and catch per unit effort (CPUE) increased with rainfall and lake depth up to the year 2000, after which they decreased, despite an increased rainfall level. The lake depth was positively correlated with the average total length and length at 50% maturity (r = 0.991 and 0.726, respectively), while the slopes of the length–weight relationships differed significantly between high and low lake depths [t(6) = 3.225, P < 0.05]. Nile tilapia shifted from an algal-dominated diet during the wet season to include more insects during the dry season. The results of this study indicate Nile tilapia in Lake Wamala displays a typical r-selected reproductive strategy, by growing to a small size, maturing faster and feeding on different food types, in order to survive high mortality rates under unfavourable conditions attributable to higher temperatures, low rainfall and low lake water levels.
  • Thumbnail Image
    Item
    Status of Kigezi minor Lakes: A limnological survey in the Lakes of Kisoro, Kabale and Rukungiri Districts
    (International Journal of Water Resources and Environmental Engineering, 2016) Dias M. Tibihika, Papius; Okello, William; Barekye, Alex; Mbabazi, Dismas; Omony, Jimmy; Kiggundu, Vincent
    A limnological survey was conducted in six Lakes: Mulehe, Mutanda, Kayumbu, Chahafi, Bunyonyi and Nakasanda, of South-Western Uganda (SWU) in September 2014. The baseline survey aimed at characterizing the high altitude water bodies for enhanced future fisheries productivity. The results indicated that Lake Nakasanda had the highest temperature (24°C). Although other physic-chemical conditions of the water bodies varied, they were within acceptable ranges for fish productivity with no extreme cases reported. Chlorophyll-a was recorded highest in Lakes Nakasanda (16.8±3.4 μgL-1) and Bunyonyi (14.2±9.5 μgL-1). Rotifers were the most dominant zooplankton taxa with a total of 16 species and Lake Mulehe had the highest abundance (2,089,423±4,511 individuals m-2) while the least abundance were recorded in Lakes Nakasanda (471,608±35,505 individuals m-2) and Chahafi (473,354±15,279 individuals m-2). Among the macro-invertebrates, Diptera was the most abundant with Lake Mutanda recording the highest species richness of 8. The recorded absence or fewer individuals of some zooplankton and macro-invertebrate species/groups in certain aquatic ecosystems were attributed to the water quality. The variation in water quality, results from human activities and this may impart negative implications on fish productivity if not remedied.