Occurrence of fish larvae in the St Lucia Estuary, KwaZulu-Natal, South Africa

Abstract

Abstract Ichthyoplankton samples were collected over 12 consecutive months. at a fixed station 4 km upstream from the mouth of the St Lucia Estuary, in order to study the recruitment of fish larvae into the estuary. In all, 51 690 fish larvae, representing 44 families and 85 species, were collected. The Gobiidae and the Clupeidae were the two dominant families, representing 74 and 19% of the larvae respectively. The most abundant species were the river go by Glossogobius callidus and the estuarine round herring Gilchristella aestuaria, which contributed 67 and 19% respectively. The proportion of species which are dependent on estuaries to some degree contributed 54% of the total number of taxa. Environmental variables correlated with larval densities in each estuarine-association group and were species-specific. Turbidity and salinity accounted for 45% of the variation in larval densities in the estuarine-dependent group, where densities were greater at higher turbidities and lower salinities. Densities of larvae peaked between November and April (late spring, summer and autumn) and declined to a minimum between the end of May and August (late autumn and winter). Densities of larvae of estuarine-spawning species were much higher than those of marine spawners and peaked in spring, summer and autumn. Densities of larvae of species spawning in the sea were greatest during autumn. A significant proportion of the larvae of marine species recruiting into the St Lucia Estuary is at the postflexion, developmental stage. It is concluded that the St Lucia Estuary fulfils an impol1ant role as a nursery ground for early life history stages of many of the fish utilizing the St Lucia estuarine system.