Ichthyofauna of the sub-tropical Nhlabane Estuary, KwaZulu-Natal: drought-related changes in the fish community during extended mouth closure

Abstract

The fish fauna of the Nhlabane estuary in northern KwaZulu-Natal was studied during a drought over the period 1992–95. The estuary mouth closed in late 1991, due to the drought as well as water abstraction from the system, and only reopened when the drought ended in late 1995. Fish were sampled by seine and gill-netting. Of 40 species recorded, most were estuarine-dependent marine species. Marine and estuarine dependent species dominated during 1992, whereas freshwater and resident estuarine species dominated in 1995. Estuarine-dependent marine species declined most in number and abundance and were most affected by the low salinities and lack of marine influence due to the lack of post-larval recruitment and the loss of the nursery function of the estuary. Exploitation of the Nhlabane system as a water resource also contributed to the extended mouth closure and the decline in the fish community. Limited post-larval recruitment by means of wave-overtopping did, however, appear to continue even though the estuary mouth remained closed.