Distribution patterns of fishes in a freshwater deprived Eastern Cape estuary, with particular emphasis on the geographical headwater region

Small seine net fish assemblages in the headwater region of the Kariega Estuary are described and compared to the catch composition in other parts of the system. The geographical headwaters of the freshwater ‘deprived’ Kariega Estuary were utilised by a range of fish species but, in contrast to the nearby freshwater ‘rich’ Great Fish Estuary, few important angling species (e.g. spotted grunter Pomadasys commersonnii and dusky kob Argyrosomus japonicus) were recorded. The reduced riverine flow into the Kariega Estuary resulted in an extremely restricted river-estuary interface (REI) zone being made available to resident and migrant fish species. Despite the low freshwater input recorded, the catadromous freshwater mullet Myxus capensis was abundant within the REI zone and headwater reach, probably due to reduced access to riverine habitat above the estuary. Although salinity has been shown to be an important structuring force influencing ichthyofaunal assemblages in many South African estuaries, it is not the primary factor governing the distribution of fish in a freshwater-deprived, marine-dominated system such as the Kariega.