The Diet of Limnothrissa miodon and Zooplankton Densities in Sanyati Basin, Lake Kariba

Abstract

There has been a continuous decline in the catches of Limnothrissa miodon in Lake Kariba since 1994. Given the value and contribution of this sardine in the GDP (gross domestic product) of Zimbabwe, research on its ecology becomes vital. The diet composition of L. miodon in the Sanyati basin of Lake Kariba was explored using numerical and frequency of occurrence methods. Densities of zooplankton species in the riverine and pelagic zones of the basin were established. Zooplankton species were collected at each site using 60 μm mesh plankton, preserved and classified in the laboratory. Limnothrissa miodon samples (500 g) were collected from Kapenta rigs for gut analysis. Diet overlap and relative prey selection was analysed using Schoener index and Chesson's index of selection respectively. ANOVA was done to establish the variations in the zooplankton densities in the riverine and pelagic sampling areas as well as proportional occurrences of prey item consumed. Significant differences on proportions of chironomids (F = 1.94, P ＜ 0.05), nauplii (F = 10.24, P ＜ 0.05) and Diaphanosoma (F = 20.98, P ＜ 0.05) preyed by Kapenta size classes in riverine specimens were noted. Proportion of chironomids and Bosmina eaten by adult and sub-adult Kapenta in pelagic waters were significantly different (F = 2.55, P ＜ 0.05) and (F = 2.21, P ＜ 0.05). A hierarchical cluster analysis using species densities revealed no major divisions in faunal associations among cyclopoids. Findings of this study indicate that the densities of zooplankton species between pelagic and riverine sections of the Sanyati basin are different.