Fish assemblages in the Mfolozi-Msunduzi estuarine system, KwaZulu-Natal, South Africa, when not linked to the St Lucia mouth

The fish community of the Mfolozi-Msunduzi estuarine system was investigated with particular emphasis on its role as a nursery area for marine fish when the adjacent St Lucia mouth is closed. The mouth was open during March 2007 and 2008 with high-turbidity river water flowing into the sea, and was closed during August 2007 and 2008. Fish were sampled biannually with seine-nets during March and August in 2007 and 2008 at five sites throughout the system. A total of 5 886 fish from 59 species were recorded, with a higher number of species and CPUE in the Mfolozi Estuary than in the Msunduzi Estuary. Seine-net catches were dominated by Ambassis gymcocephalus, Ambassis natalensis, Leiognathus equula and Valamugil cunnesius. Juveniles of marine spawning species were present throughout the study period, even when the mouth was closed. The sampled fish assemblage structure was influenced by significant temporal differences between the four biannual sampling seasons, with relatively small spatial differences between the sampling areas. Temperature, salinity and sediment characteristics were most responsible for the structure of the fish assemblage as sampled by seine-nets. The results emphasise the importance of the Mfolozi-Msunduzi estuarine system as an alternate nursery area.