Response of demersal fish assemblages to an extreme flood event in a freshwater-deprived estuary in South Africa

The Kariega Estuary in South Africa, is an example of a freshwater-deprived estuary. Large-scale water abstraction and droughts have resulted in this estuary either being uniformly marine or hypersaline. A major episodic flood event in October 2012, the largest ever recorded in this system, provided us with an opportunity to investigate the prolonged effect of an episodic flood on the demersal fish assemblage of a freshwater-deprived estuary. A beam trawl net was used for sampling the fish assemblages from December 2013 to November 2014. The flood event before the sampling period 'reset' the system, such that there was a longitudinal salinity gradient from the head to the mouth, which resulted in 'normal in 'normal' estuarine conditions, typical of most estuaries. There was an increase in the abundance of benthopelagic marine migrant species, particularly early juveniles of important fishery species, in the middle and upper reaches during the present study relative to previous studies conducted in this freshwater-deprived system. This suggests increased recruitment of these species into their estuarine nursery habitat. The present study highlights the importance of understanding the effect of freshwater inflow on the demersal estuarine fish assemblage and the nursery role of this and other estuarine systems and their management.