Content uploaded by Edward Ndirui Kimani
Author content
All content in this area was uploaded by Edward Ndirui Kimani on Jan 06, 2020
Content may be subject to copyright.
A preview of the PDF is not available
The status of Kenya Fisheries KMFRI 2018
Figures
Figures - uploaded by Edward Ndirui Kimani
Author content
All figure content in this area was uploaded by Edward Ndirui Kimani
Content may be subject to copyright.
ResearchGate has not been able to resolve any citations for this publication.
Hydrological regimes are significant drivers of fisheries production in many African Lakes due to their influence on fish habitat and food availability, breeding success, and catchability. Lake Turkana, Kenya will undergo substantial changes in hydrology due to water regulation and extraction along the Omo River in neighboring Ethiopia, which provides over 90% of its water. The objective of this study was to predict how the lake's fisheries, which provide an important livelihood and protein source in the region, will respond to hydrological change. While variations in fishing effort are poor predictors of fisheries catch in the lake, water levels and their fluctuations strongly influence fisheries production. Seasonal oscillations play a particularly important role and with complete loss of these oscillations the lake's predicted fisheries yield will decrease by over two thirds. The fishery is predicted to collapse at a lake level decline of 25 m, regardless of seasonal amplitude magnitude. The lake's total littoral habitat, where fisheries are currently concentrated, will increase in surface area with lake level declines of <25 m. However, the extent of productive, dynamic littoral habitat will decrease with dampening of the lake's seasonal oscillations. The most severe habitat loss will occur in the lake's Turkwel Sector, which hosts the region's highest human population densities, and North Sector, where inter-tribal conflict over resources is common and likely to be exacerbated by lake level decline. The continued ecological functioning of Lake Turkana necessitates immediate efforts to develop and apply a water resource management plan rooted in science.
Unlike most of the small lakes in the Rift Valley, Lake Naivasha is fresh despite the absence of an exit river. The most likely reason is that the dissolved substances in the input are dilute, biochemical and chemical processes are in place to remove ions such as sulphates and carbonates and there is seepage from the lake bottom (Harper et al., 1990). Because the lake is fresh, there might be an expectation of a rich fish fauna, in line with the diversity found in other lakes such as Victoria and Malawi. It comes as a surprise to many that the fish fauna is sparse and contains mostly introduced species. In the past, these have died out after only a few years. A clue to the low fish diversity, and to the frequent extinctions, may lie in the variability that is characteristic of the water level, the abundance of the aquatic macrophytes and the limnological conditions. In the face of this variability, three fish species and a crayfish form the basis of a commercial fishery that has lasted for 30 years.
WWF-Eastern Africa Regional Programme Office (WWF-EARPO), through its freshwater programme, began the task of establishing the Reserve flows for Mara River in 2006. The first two site assessments covering three sites were conducted in March and July 2007 by a team of specialists comprising a geomorphologist, hydrologist, hydraulic engineer, aquatic ecologist, riparian ecologist, water quality specialists, and socioeconomist. The first Reserve flows for the river were prescribed in October 2007 during the EFA workshop held in Narok, Kenya. At this workshop it was also agreed that continued monitoring of the river’s flow levels and ecological status is critical to improve the accuracy of the prescribed flows.
The present work reports on the results of a fish sampling exercise conducted in February 2009 during the third assessment for the Mara River. The assessment covered one additional site in the Nyangores River and coincided with the period of low flows in the Mara River.
The water and bottom sediments of Lake Victoria (Kenya) were analysed for A1, Fe, Mn, Zn, Pb, Cu, Cr and Cd. The total metal concentrations were determined and their mean variations and distributions discussed. The bottom lake waters showed higher concentration levels than the surface waters. The range of values (in mg/l) in the bottom and surface lake waters were as follows:
Surface Waters: A1(0.08 - 3.98), Fe(0.09 - 4.01), Mn(0.02 - 0.10). Zn(0.01 -0.07),
Pb(0.001- 0.007), Cu(not detected - 0.006), Cr(not detected - 0.004).
Bottom Waters: A1(0.1 0 - 6.59), Fe(0.23 - 9.64), Mn(0.04 - 0.39),
Zn(0.01- 0.08), Pb(0.002 - 0.009), Cu(not detected - 0.03). Cr(not detected -0.002).
River mouths and shallow areas in the lake showed higher total metal concentrations than offshore deeper areas. Apart from natural metal levels, varied urban activities and wastes greatly contribute to the lake metal pollution as shown by high Pb and Zn levels in sediments, around Kisumu and Homa Bay areas. Other comparatively high values and variations could be attributed to the varied geological characteristics of the lake and its sediments. Compared to the established W.H.O (1984) drinking water standards manganese, aluminium and iron levels were above these limits whereas zinc, lead, chromium, copper and cadmium were below.
The present ecological and hydrological state of Lake Naivasha, a tropical freshwater Ramsar site, is reviewed from existing research. The ecology of the lake was formerly regulated by ecohydrological control exerted on the inflowing hydrochemistry by the continuous fringing papyrus, with a full swamp on the inflow rivers' delta. The ecology of the lake since that time has been severely disrupted by alien (or exotic) species invasions, particularly the Louisiana crayfish Procambarus clarkii. Lake-wide papyrus degradation has also been occurring since about 1980, following a lake level decline of up to 3m through agri-industrial abstraction. The river Malewa, which previously ran through a swamp, now runs directly into the lake, bringing high silt and nutrient loads in wet seasons, making the lake eutrophic. It is suggested that sustainable management of the lake should focus upon three ecohydrological objectives - control of abstractions to achieve hydrological balance, physical restoration of the former North Swamp and the control of illegal fishing. The latter would enable the commercial fishery returns to maximum sustainable yield so that large M. salmoides (large mouthed bass) individuals once again impose a 'top-down' control upon P. clarkii, and the crayfish itself be commercially exploited.