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Changes in the fisheries of Lake Malawi, 1976-1996: ecosystem-based analysis

University of British Columbia

Lake Malawi is one of the most species-rich freshwater bodies in the world. Conservation of aquatic resources in the lake, however, competes with the need to provide for food and livelihood for a majority of adjacent fishing communities. The lake is therefore impacted by both anthropogenic and environmental factors. This study looks at the changes in the fisheries of Lake Malawi between 1976 and 1996 using ecosystem-based analyses. Four analyses are carried out. First, the fisheries are evaluated by using a rapid appraisal technique, 'Rapfish', to assess their health status in sustainability terms. Second, a new Ecopath model is constructed to show the trophic structure of the Lake Malawi ecosystem. Third, maximum lengths and trophic levels are analysed to establish the extent of decline in fish size. Finally, alternative policies for exploiting the lake are explored using the Ecosim, which is an ecosystem simulation routine. Application of the rapid appraisal technique on the species-based fisheries shows that the health status has worsened with time. It shows further that the gear-based fisheries are healthier when the operation level is small rather than large. Twenty-six trophic groups are quantified in the Ecopath model and three of these, lakefly Chaoborus edulis, Engraulicypris sardella larvae and predatory zooplankton Mesocyclops aequatorialis, form the main pathway through which energy flows from the bottom to top trophic levels in the lake's ecosystem. The trophic structure of Lake Malawi deteriorated over time. Detritus is less important in the lake's energy flow. Maturity of the lake ecosystem is between early and middle stages. Both mean maximum length and trophic level of fish caught in the lake declined with time. However, decline in the latter is masked by the decrease in catches of more herbivorous fish with low trophic levels and an increase in landing of small sized fish with high trophic levels. The traditional sector influences the lake's fisheries and ecosystem more than the commercial sector. A number of species-based fisheries, apart from Chambo Oreochromis spp. are exploited at above their maximum sustainable levels.

Thesis/Dissertation

application/pdf

2009-07-07

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http://hdl.handle.net/2429/10334

Resource Management and Environmental Studies

University of British Columbia

UBCV

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