| Summary: | The early life history of the freshwater sardine Limnothrissa miodon (Boulenger, 1906) was
investigated with the view of establishing the factors behind recruitment variability in the
Lake Kariba sardine fishery. Environmental factors behind recruitment variability were
investigated through the examination of otolith microstructure from field captured sardine
larvae samples while historical length-frequency data were analysed to establish size-at-recruitment.
The larval ecology study established that food was the only possible limiting factor as far as
growth and survival are concerned. Growth was described by the von Bertalanffy Growth
Function while instantaneous mortality rates were obtained from catch curve analysis and
both estimates were observed to fluctuate from month to month. The presence of larvae in
the littoral zone through the sampling period implied continuous recruitment while fluctuation
in larval catches was assumed to indicate that recruitment variability was probably established
at an earlier life history stage. Response of larvae to light during capture has serious
management implications to the fishery in that fishing in shallow areas would result in
increased larval mortality which could be detrimental to recruitment. The occurrence of
larvae in most of the shoreline sampled implies that Limnothrissa miodon in Lake Kariba
utilizes most of the shoreline as nursery grounds.
From analysis of combined historical commercial data collected from both Zambia and
Zimbabwe from 1982 to 1992, it was observed that the sardine recruited to the fishery at 41
mm in length and that based on regression analysis, the mean size of fish in the fishery has decreased by 7% and 4% in Zambia and Zimbabwe respectively. This reduction in size
however, does not pose a threat to the fishery since at the current mean size in the catch is
greater than the recorded size-at-maturity. The fish therefore have a chances of spawning at
least once before being harvested. It was further established that due to migration to the
pelagic zone as the fish grew larger, the current minimum mesh size of 8 mm was
appropriate provided fishing was restricted to areas deeper than 15 m where the adult
population occurs. === Science, Faculty of === Resources, Environment and Sustainability (IRES), Institute for === Graduate
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