Dynamics of the feeding ecology of selected fish species from the Okavango River delta, Botswana

Abstract

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.

Classical Fisheries Theory and Inland (Floodplain) Fisheries Management; Is there Need for a Paradigm Shift? Lessons from the Okavango Delta, Botswana

“…Their study revealed that most fish species from the delta are opportunistic feeders whose diet is changed seasonally regulated by the seasonal flood pulse. In fact, the feeding rate of some fish species is driven by changes in either mean depth or discharge [80]. This study [80] revealed that fish diet varied between terrestrial and aquatic sources, depending on the seasonal hydrograph.…”

“…The majority of fish species are insectivores (Table 1), which highlights the importance of insects/ aquatic macroinvertebrates in fish biomass production in the delta. This notwithstanding, the delta's fish species have a relatively plastic feeding behavior [79,80], because of the dynamic nature of the system. Schilbe intermedius is one of the dominant species in the delta's fish community [79,81], possibly due to its opportunistic feeding ecology [79,81], where it also feeds on terrestrial food items, driven by the seasonal flood pulse [80].…”

“…This notwithstanding, the delta's fish species have a relatively plastic feeding behavior [79,80], because of the dynamic nature of the system. Schilbe intermedius is one of the dominant species in the delta's fish community [79,81], possibly due to its opportunistic feeding ecology [79,81], where it also feeds on terrestrial food items, driven by the seasonal flood pulse [80]. Cichlids are the dominant family in the delta's fish community [81], and Mosepele [80] also found out that they have a plastic feeding behavior, where detritivorous species like Oreochromis andersonii were found to prey on fish under stressed conditions.…”

“…Furthermore, Mosepele et al [81] also observed habitat partitioning in fish species assemblages of the delta, where upper delta habitats have relatively higher species diversity than lower delta habitats [79]. Several studies have shown that the flood pulse is a key driver in the delta's fish community [75,80,[84][85][86]. Similar fish species from different habitats in the Delta have different life history strategies [82,87], which is driven primarily by differences in environmental conditions [85].…”

“…Similar fish species from different habitats in the Delta have different life history strategies [82,87], which is driven primarily by differences in environmental conditions [85]. Furthermore, Mosepele et al [80] showed that the seasonal flood pulse is the major driver of the feeding ecology of selected fish species from the Okavango Delta. Their study revealed that most fish species from the delta are opportunistic feeders whose diet is changed seasonally regulated by the seasonal flood pulse.…”