Changes in catches and biological characteristics of Nile tilapia (Oreochromis niloticus Linnaeus) in Lake Wamala (Uganda) under changing climatic conditions

There have been changes in catches and biological characteristics of the Nile Tilapia, Oreochromis niloticus (Linnaeus) in Lake Wamala (Uganda) since its introduction and establishment, but the factors which have contributed to these changes are not adequately understood. This study examined changes in catches and biological characteristics of Nile tilapia in relation to changes in temperature, rainfall and lake depth to provide an understanding of the role of changing climatic conditions. There was an increase in minimum, maximum and average temperature since 1980, but only minimum (0.021ºCyr-1) and average (0.018ºCyr-1) showed a significant trend (p < 0.05). Rainfall increased by 8.25 mmyr-1 since 1950 and accounted for 79.5% of the water input into the lake while evaporation accounted for 86.2% of the water loss from the lake. The lake depth was above 4 m during the years rainfall was above normal average of 1180 mm, except during the period 2011-2014. The contribution of Nile tilapia to total catch and CPUE changed with rainfall and lake depth up to 2000, after which they decreased despite increase in rainfall. There was a strong positive correlation between lake depth and average total length of Nile tilapia (r = 0.991, p < 0.001) and length at 50% maturity (r = 0.726, p < 0.001). The length-weight allometry between high and low lake depths was significantly different [t (6) = 3.225, p < 0.05], with Nile tilapia being heavier (for a given length) at high lake depth than at low lake depth. Fecundity of Nile tilapia was higher and egg diameter lower than what is reported in literature. Nile tilapia shifted from algal dominated diet during the wet season to include more insects during the dry season. The study showed that the catches and biological characteristics of Nile tilapia change with climate and hydrological factors and these need to be considered in management of the fisheries of Lake Wamala.

WorldFish Center report on the opportunities and constraints to improved fisheries exploitation and management in the Maringa – Lopori – Wamba landscape

The WorldFish Center was contracted by Africa Wildlife Foundation to conduct a preliminary survey of the role of fisheries in livelihoods, and opportunities and constraints to improved fisheries exploitation and management, in the Maringa-Lopori-Wamba Landscape. In May 2007, a three person WorldFish Center team, supported by AWF staff, visited the landscape to explore how the fishery operates to meet local needs and identify scope for interventions that might improve fisheries livelihood opportunities without undermining its sustainability. It is clear that although fishing is important for both income and subsistence in the areas visited, profits are nonetheless modest and somewhat unpredictable. Moreover, fisherfolk should not be considered a homogeneous group: there are different sub-groups, using different gears and skills, involving women and men in both fishing and post-harvest activities, groups who are more or less dependent on farming, and who fish, on balance, more either for cash or subsistence needs. Thus the findings here need to be set within this context of different sub-groups, fishing for generally very modest remuneration, with the latter subject to considerable variability and uncertainty.