Fish larval composition, abundance and seasonality in a southern African estuarine lake

Abstract

The ichthyoplankton community of Swartvlei, an estuarine lake on the southern Cape coast, has a low species diversity (< 10 species) owing to the tenuous link with the marine environment and paucity of fishes breeding in South African estuaries. The larval assemblage was dominated by the clupeid Gilchristella aestuaria, which was distributed across the entire lake and comprised 78% of the total catch. Mean annual ichthyoplankton abundance was relatively low (38 larvae 100 m⁻³), possibly as a result of the extremely low phytoplankton productivity and poor zooplankton biomass. Fish larvae and zooplankton peak in abundance between October and March, with very low densities recorded for the remainder of the year. During a 24 h sampling session In February 1988, ichthyoplankton abundance increased significantly (p < 0,001) in surface waters after sunset and declined following sunrise.