M.J Ntiba

Mitigation of environmental problems in Lake Victoria, East Africa: causal chain and policy options analyses

Abstract Lake Victoria is an international waterbody that offers the riparian communities a large number of extremely important environmental services. Over the past three decades or so, the lake has come under increasing and considerable pressure from a variety of interlinked human activities such as overfishing, species introductions, industrial pollution, eutrophication, and sedimentation. In this paper we examine the root causes for overfishing and pollution in Lake Victoria and give possible policy options that can help remediate or mitigate the environmental degradation.

Environmental assessment of the East African Rift Valley lakes

An assessment of the East African Rift Valley lakes was initiated by the United Nations Environment Programme (UNEP) with funding from Global Environment Facility as part of the Global International Waters Assessment (GIWA). The purpose of GIWA was to produce globally comparable assessments and examine stresses on international waters: marine, coastal and fresh; surface and groundwaters. The assessment of the East African Rift Valley lakes was undertaken from the perspective of water quality and quantity, associated biodiversity and habitats, their use by society and societal causes of the regionally identified issues and problems. Assuming intrinsic values of aquatic ecosystems, the assessment of social perspective focused on human use of water and considered the incremental costs of measures to encourage sustainable development. The assessment identified the major concerns facing the East African Rift Valley lakes.By and large, pollution and unsustainable exploitation of fisheries and other living resources emerged as critical concerns attributable to human activities. East Africa has a very high concentration of humans and economic activities. Pollution is from uncontrolled discharge of wastes directly into the lakes. Unsustainable exploitation of fisheries and other living resources is caused by over-fishing, destructive fishing practices, and introduction of non-native species that affect the composition of the native communities, resulting sometimes in the collapse of certain species and dominance by resilient ones. Loss of biodiversity also was identified as a major concern; and the issues of excessive by-catch and discards are also relevant. Trawling using undersized mesh-nets for target species and indiscriminate fishing gear or poison is serious, in most cases resulting in indiscriminate catches, including juvenile fish. Given the transboundary nature of the issues identified in this assessment, appropriate multilateral policy and institutional arrangements need to be established in East Africa to address the main concerns of these large lakes. Riparian countries must pay attention to the regional management of these transboundary water bodies, and appropriate planning of human population sizes and their settlement, land-use and waste disposal to control pollution. Although East African lakes contribute relatively little emission of greenhouse gases, there is a need to reduce the rate of deforestation and even restore cleared areas since forests serve as sinks of greenhouse gases towards mitigating adverse climatic changes.

Key elements of fisheries management on Lake Victoria

The fisheries of Lake Victoria have always been dynamic and the relevant authorities have continually tried to manage them. During the second half of the last century, numerous changes took place and fisheries managers had to cope with influences other than exploitation, including species introductions, invasive weeds, lake level rise, changes in water quality, and illegal fishing practices. These have influenced the way the fisheries have been managed. In the 1920s, measures existed to manage the fisheries of Lake Victoria. In those days, a minimum net mesh size of one inch was in place, as well as certain restrictions for trawling and other fishing methods. Over the years, certain fishing gears and methods have been banned; some bans were lifted and then reimposed; minimum mesh sizes have shifted as a result of changing species compositions and changing needs to protect components of the stock. More recently, the fishery has been subjected to a series of bans on export to the European Union because of outbreaks of cholera and fish poisoning practices. This article presents an overview of fisheries management on Lake Victoria, the successes and failures, impacts of fish exploitation and invasive weeds on species diversity, results of a major research project on the lake to assess the status of the fisheries, and the way forward.

The effect of overfishing on the life-history strategies of Nile tilapia, Oreochromis niloticus (L.) in the Nyanza Gulf of Lake Victoria, Kenya

Studies were conducted on reproductive characteristics of Oreochromis niloticus from 1998 to 2000. The results were combined with published work on growth parameters of O. niloticus from 1985 to 1999 in order to establish the current survival strategies exhibited by O. niloticus in the Nyanza Gulf of Lake Victoria. The study revealed that size at maturity had decreased concurrently with increasing fishing mortality. Observations on reproductive effort point to a fish species under stress. It is observed that the behavioural change in O. niloticus is not due to size selective predation but due to size selective exploitation. Indications that O. niloticus in the Nyanza Gulf of Lake Victoria allocates more energy for reproduction than for somatic growth (i.e. increased turnover rate) are multiple. It is concluded that O. niloticus in the Nyanza Gulf exhibits an ‘r’-selected life history strategy in order to survive stressful conditions.

Some observations on the spawning season of Barbus amphigramma in Lake Naivasha, Kenya

The objective of the study was to investigate some aspects of the breeding patterns of the cyprinid Barbus amphigramma in Lake Naivasha. The study was carried out from February to October, 2003. Fishing was done with the use of gillnets of mesh size 0.5 inch to 3 inch and a beach seine of mesh size 1 inch. Six gonad maturity stages have been described visually, based on morphological features, and validated by histological features of the ovary, as well as examination of the oocyte diameter. Females dominate the population at all sizes classes. Barbus amphigramma spawns all year round, but with discernible peaks in March, July and October. The peaks in March and October correspond with the beginning of the long and short rains, respectively, in Kenya.