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Habitat Degradation and Subsequent Fishery Collapse in Lakes Naivasha and Baringo, Kenya

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Habitat Degradation and Subsequent Fishery Collapse in Lakes Naivasha and Baringo, Kenya Habitat degradation and subsequent fishery collapse in Lakes Naivasha and Baringo, Kenya. Item Type Journal Contribution Authors Hickley, P.; Muchiri, M.; Boar, R.; Britton, R.; Adams, C.; Gichuru, N.; Harper, D. Download date 30/09/2021 12:47:36 Link to Item http://hdl.handle.net/1834/7302 Vol. 4 No 4, 503-517 2004 Habitat degradation and subsequent fishery collapse UNESCO IHP EIFAC FAO in Lakes Naivasha and Baringo, Kenya Ecohydrology and physical fish habitat modifications in lakes Phil Hickley1, Mucai Muchiri2, Rosalind Boar3, Robert Britton1, Chris Adams1, Nicholas Gichuru4, David Harper5 1National Fisheries Technical Team, Environment Agency, Arthur Drive, Hoo Farm Industrial Estate, Kidderminster, DY11 7RA, UK, e-mails: [email protected], robert.britton@environment- agency.gov.uk, [email protected] 2Department of Fisheries, Moi University, P.O. Box 3900, Eldoret, Kenya, e-mail: [email protected] 3Centre for Ecology, Evolution and Conservation, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK, e-mail: [email protected] 4Kenya Marine & Fisheries Research Institute, P.O. Box 81651, Mombasa, Kenya, e-mail: [email protected] 5Department of Biology, University of Leicester, Leicester LE1 7RH, UK, e-mail: [email protected] Abstract Lakes Naivasha and Baringo in the eastern Rift Valley of Kenya are shallow, fresh- water lakes that are subject to major fluctuations in water level and suffer from habi- tat degradation as a consequence of riparian activity. Lake Naivasha is approxi- mately 160 km2, is bordered by Cyperus papyrus and its aquatic macrophytes are in a state of flux. The most significant riparian activity is the large scale production of flowers for the European market. Lake Baringo is approximately 140 km2 and lies in a semi-arid region. Its most noticeable feature is its extreme turbidity which is mainly due to excessive soil erosion resulting from deforestation and overgrazing. This turbidity has led to near extinction of submerged macrophytes and a lake bed virtually devoid of benthic fauna. Fishing pressure has added to the environmental stresses being endured by the fish populations and commercial catches have been detrimentally affected. Accordingly, periods of fishery closure are now imposed upon both lakes. Limited remedial action is feasible and some local stakeholders are attempting to introduce mitigation measures. For Lake Naivasha there is an agreed riparian owners' management plan which tackles issues such as water usage and pro- tection of the C. papyrus margin. For Lake Baringo there is a Rehabilitation of Arid Environments initiative which promotes such activities as restoration of riparian vegetation and appropriate stock management. Key words: Rift Valley lakes, ecohydrology, fish, macrophytes, turbidity, soil ero- sion. 504 P. Hickley et al. 1. Introduction brackish or saline. Bathymetric maps and associat- ed information are given in Figs 1 and 2. Ecohydrology is the scientific concept that Lake Naivasha is approximately 160 km2, is promotes the integration of hydrology and ecolo- 190 km south of the equator at an elevation of gy and the control of these processes to enhance 1890 m a.s.l. and is semi-arid (Agro Climatic Zone the absorption and assimilation capacity of 5). It is bordered by Cyperus papyrus swamp. ecosystems (Zalewski et al. 1997). Methodo- Rainfall is around 680 mm with two rainy seasons. logies include using hydrological processes to Soils are silt loam to clay with a humic topsoil in control biota and as such can provide an effective many places and well drained (although in places, and efficient mechanism for the restoration of poorly drained). Particles from eroded topsoil are degraded environments and associated sustainabil- intercepted the fringing papyrus. Riparian owner- ity of society. Freshwater ecosystems accumulate ship of lake Naivasha is private. the impacts of human activities and consequently Lake Baringo is approximately 140 km2, is the quality of fish habitat depends to a large extent 60 km north of the equator, lies in the Rift Valley upon the density of the human population and its floor at 900 m a.s.l., and has a semi-arid climate. activities within the basin (Zalewski, Welcomme The littoral community is poorly developed 2001). This paper describes the detrimental impact around much of the lake. Being in the Intertropical of degraded environments on two important Convergence Zone (ITCZ) the lake has two rainy Kenyan fisheries and how starting to control the seasons with annual rainfall around 600 mm. Soils key catchment and riparian processes could lead to are clay and clay loams and the risk of soil erosion fishery restoration and sustainability. is high because of the soil properties (clay fills pores or seals the surface giving low infiltration Site descriptions capacity). Forty-six percent of the land in the dis- trict is too steep or too dry for agriculture and pas- Lakes Naivasha and Baringo are shallow, toralism is the main source of family income. freshwater lakes in the eastern Rift Valley of Riparian use and ownership is variously private Kenya. Other lakes in the Kenyan Rift Valley are and communal. LAKE LAKE NAIVASHA BARINGO N 4 m 2.5 m 3.5 m 3 m 2 m 3 m 4.95 m 1.5 m 4 m 2 m 1 m 5 m 16 m 6 m 7 m Depth contours 5.95 m at 1 m intervals Depth contours 3 m 6.5 m 2.5 m at 0.5 m intervals (excluding 0.5, 1m) 0123 4 5 km Islands 0123km 2 m 1.5 m Scale: Scale: Fig.1. Bathymetric maps for Lake Naivasha (August 1991; after Hickley et al. 2002) and Lake Baringo (August 2003). Contour lines are 1 m and 0.5 m (commencing at 1.5 m) intervals respectively. Spot depths for deepest points shown; contour lines <3m around Baringo islands not shown. Habitat degradation and fishery collapse in L. Naivasha and Baringo, Kenya 505 % lake surface area (a) Cumulative % lake area (b) 05010001020304050 0 0-1 10 20 Naivasha : 1-2 Dmean = 3.35 m 30 Dmax = 7.0 m D50 = 3.8 m 2-3 40 50 3-4 % depth (m) 60 Depth zone (m) Baringo : 4-5 70 Dmean = 2.65 m Dmax = 4.1 m 5-6 80 D50 = 3.05 m 90 6-7 Naivasha Baringo Naivasha Baringo 100 Fig. 2. (a) Percentage hypsographic curves for Lakes Naivasha (August 1991, solid line) and Baringo (August 2003, dotted line) with values for mean depth (Dmean), maximum depth (Dmax) and 50 percentile depth (D50); (b) Percentage of lake area underlain by each depth zone for Lakes Naivasha (plain bars) and Baringo (black bars). Pressures on the lakes and cultivation of sisal gave way in recent years to the present irrigated horticulture. Horticultural The Rift Valley lakes of Kenya are of impor- technology, with its attendant use of pesticides tance to national economy as natural assets, par- has grown dramatically over the past two decades ticularly in the context of tourism. In addition, and this has been accompanied by cultivation those such as Naivasha and Baringo, which are fresh enough to support Happiness Nothing fish populations, provide support to Beauty the local economy by enabling a Power Fishing fishing industry. Local opinion on Climate the importance of Lake Naivasha is Tourism & Foreign represented by Fig. 3. Lake exchange Naivasha became a Ramsar site in April 1995 (Wetlands International Ecology & 2001) and Baringo in January 2002 Science (Ramsar 2001) but the pressures on Washing the lakes' ecosystems and thus on the sustainability of their fisheries are considerable. Both lakes are subject Wildlife to major fluctuations in water level Livestock Drinking and habitats are degraded as a con- watering water sequence of riparian activity. The most significant riparian activity on Lake Naivasha is the Farming large scale production of flowers for Irrigation the European market and at least Employment 50% of the perimeter of the lake is Fig. 3. Principal reasons for Lake Naivasha being considered by the under agriculture of some descrip- local community to be important. Pie chart is a breakdown of 119 tion. Former stock-rearing, ranching answers given by 62 people (see methods). 506 P. Hickley et al. close to the lake. Also, as the labour intensive stant speed along 32 tracks of total distance 104 flower industry developed, so did the need for km, the positions of which were monitored with a housing, water and latrines (Enniskillen 2002). Garmin 12 hand held GPS receiver. To optimise The local population is approximately 250 000. survey accuracy, a system of tracks crossing the The lake resources are also of critical importance main track was used (Hakansono 1981). For each to geothermal electricity generation, tourism, paper echo-recording chart, the positions along wildlife and conservation (Harper et al. 1990). the track line at which depths at 0.5 m intervals Lake Baringo's most noticeable feature is its occurred were plotted on a plan outline of the lake extreme turbidity which is mainly due to soil ero- and joined to form contour lines. The lake outline sion. This results from low vegetation cover, was derived from a 1:50 000 scale map (Kenya caused by deforestation and overgrazing, exacer- Government 1982) which was based on aerial bated by high intensity, sporadic rainfall on steep photographs taken in August 1977 and January slopes. In recent years two thirds of the total 1978. Depth profiles were transcribed directly catchment (8655 km2) has been grazing and the from the echo-recording charts. Morphometrical rest of the land under agriculture, apart from <1% values were determined according to Hakanson forest. All the grazing area and two thirds of the (1981). agricultural land is environmentally degraded; The area of cover by aquatic macrophytes in almost 90% of the catchment.
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