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Technical Brief: Mapping and Assessment of Deep Pool Refugia Along the Main Rivers in the Lake Chilwa Catchment Fisheries Integration

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The affluent rivers of Lake Chilwa, including Domasi and Likangala, serve a vital ecological function as breeding sites and as refugia for adult fish during the dry season when the lake water quality becomes hostile to fish due to elevated salinities. The deep pools in the two rivers also serve as important refugia when the lake dries up (the lake has undergone moderate and severe recessions 11 times since 1900). During the recessions, artificial restocking is not required as the fish which seek refuge in the deep pools are able to recolonize the lake and re-establish the fishery. However, it has been observed that some of the deep pools in these rivers are silting up due to increasing soil erosion in the catchment and diversion of water for agriculture. Fish production data indicates that three years after the 2012 recession, Lake Chilwa is yet to recover suggesting changes in the resilience of the lake and the fishery. It is unknown how effective these refugia will perform under future climate conditions. The future sustainability of the fishery in Lake Chilwa therefore depends on understanding the vulnerability of this aspect of these deep hole refugia. The objective of this study was to analyze historic rainfall and river flow data to generate ecological and management information for preserving the ecological function of the deep pools to restock the Lake Chilwa fishery during extreme lake drying periods. 

The study used a combination of primary and secondary qualitative and quantitative data including taking measurements in a sampling of deep pools. Historical hydroclimatic data were analyzed for trends and compared with people’s perceptions regarding climate change and the status of the deep pools. A desktop reserve model was applied to assess the ecological status of the rivers (Appendix B). Water samples were collected in the rain and dry seasons of 2015/16 rain season to provide a baseline. Local communities, River Village Committees (RVCs) and Beach Village Committees (BVCs) were interviewed in April 2016 to gather local ecological knowledge and understand perceptions of existing governance structures.

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