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The hydrological regime of the Okavango River Basin is the main driver of ecological change in the delta. The delta supports a small‐scale fishery which is a source of livelihood for communities within its fringes. The fish resource is particularly important to subsistence fishers, who have limited access to socio‐economic opportunities. However, fish availability is subject to ‘concentration and dilution’ effects because of the hydrological regime. As a copying strategy, fishers use a variety of fishing methods to effectively harvest the delta’s fish community across all its trophic levels. This exploitation regime helps to maintain the delta’s species diversity and only reduces fish biomass proportionally across the different trophical levels. Furthermore, fishers have developed different fish‐processing techniques to preserve their harvest for low fishing season periods to cope with low food availability. The aim of this paper therefore, was to explore spatio‐temporal variations in fish availability and to show how the delta’s subsistence fishers cope with this dynamicity.

Mosepele K., Mosepele B., Wolski P., Kolding J. 2012. Dynamics of the feeding ecology of selected fish species from the Okavango River delta, Botswana. Acta Ichthyol. Piscat. 42 (4): 271-289.Background. This study contributes to the understanding of the potential impact of changes in flooding patterns and (potential) fish production as a consequence of upstream developments in floodplain systems. Therefore, stomachs of eight fish species from the Okavango Delta were analysed to evaluate the feeding ecology of floodplain fish (and the effect of seasonal flooding), using the delta as a case study. Materials and methods. In total, 2101 fish stomachs of eight species, representing six families, were collected (in all seasons) from the delta using experimental fishing nets, from 2004 to 2009. Frequency of occurrence, Levin's diet breadth index, Pianka's overlap index, trophic levels, and Bray-Curtis similarities were used to evaluate feeding preferences. Detrended correspondence analysis was used to study temporal variations in diet. Multiple linear regressions were used to determine the influence of flooding on diet. ANOVA and MANOVA were used to determine the level of significance among variables, while LSD post hoc analysis revealed the source of significance.Results. Cluster analysis and Pianka's index highlighted inter-and intra-specific competition for food among different species and age classes, ANOVA highlighted dynamic changes in inter-and intra-specific trophic level partitioning, while detrended analysis showed that the terrestrial environment is subsidizing the aquatic environment. Regression analysis showed that Schilbe intermedius diet was driven by discharge (F = 7.03; P = 0.045; R 2 = 0.58) while that of Marcusenius macrolepidotus was driven by water depth (F = 25.88; P = 0.04; R 2 = 0.93). Conclusion.The terrestrial-aquatic ecotone is important in fish growth of seasonal floodplains. Energy uptake is optimised through cannibalism to ensure species survival. Furthermore, species inter-relations are dynamic due to variations in food availability driven by seasonal flooding, which shortens and lengthens the food chain periodically. This dynamic relation is pronounced at low floods when predation and competition increases within the fish community. The evidence from this study has shown that predation, cannibalism, inter-and intra-specific competition are regulating factors in floodplain fish communities, driven by seasonal flooding.

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The spatial distribution of aquatic macroinvertebrates in the Okavango River Delta, Botswana, was investigated during the lowwater period in February 2003. This complements an earlier study undertaken during high-water in June 2000. Seventy-five samples were taken in a range of aquatic habitats at 29 georeference points in four focal areas: Upper Panhandle (UPH), Lower Panhandle and Guma Lagoon (LPH), Moremi Game Reserve/Xakanaka (MGR), and Chief's Island (CI). Over 180 morphospecies (approximately 63 families) were recorded during the survey. Multivariate analyses of macroinvertebrate assemblages indicated that assemblages in each of the four focal areas were at least 54% similar at morphospecies level, and 71% similar at family level, although some taxa were more or less common in different areas. Differences in macroinvertebrate assemblages were observed amongst different habitat types, with differences most pronounced between the deltaic habitats and isolated seasonally-flooded pools and temporary rain-filled pools in MGR and CI. The highest number of taxa was recorded in the MGR (125), followed by the UPH (96), CI (93) and the LPH (89) areas. The most families were recorded in the Hemiptera (11), followed by Mollusca (10), Diptera (nine), Coleoptera (nine), Crustacea (six), Ephemeroptera (six) and Odonata (four). Three families of Hirudinea and Trichoptera, and one family of Lepidoptera, were also recorded. Hydracarina were common but not identified beyond order, while Oligochaeta were less frequently recorded. With respect to the different aquatic habitats sampled, the highest number of taxa was recorded in marginal vegetation in the channels and lagoons, although inundated floodplains, floating vegetation and marginal vegetation in backwaters also supported many taxa. The fewest taxa were recorded in sediment. This survey, whilst representing a 'snapshot' of the system under low-water conditions, highlights the importance of maintaining a mosaic of aquatic habitats in the Delta. Further studies would enhance our knowledge of the aquatic macroinvertebrate biodiversity of the Okavango Delta, thereby contributing to its conservation. (Tweddle et al. 2003) -have examined its aquatic biology.