Juvenile fish recruitment through wave-overtopping into a closed subtropical estuary

Abstract

The fish fauna of the subtropical Nhlabane estuary in northern KwaZulu-Natal was studied during a regional drought over the period 1991—1995. The estuary mouth closed in late 1991, due to the drought and to water ion from the system, and reopened only at the end of the drought in late 1995. The fish community underwent considerable changes in composition and abundance, from marine-dominated during 1992 to freshwater/estuarine-dominated in 1995. The adverse effect of extended mouth closure on the fish fauna and the lack of contact with the marine environment was clearly illustrated. Due to mouth closure, recruitment of estuarine-dependent marine species almost stopped, although some recruitment by means of wave-overtopping was found to continue, even though the estuary mouth remained closed. Recruitment of twelve estuarine-dependent marine fish species was found to occur in this way, suggesting that recruitment through wave-overtopping is an important aspect of estuarine functioning during drought conditions.


Keywords: recruitment; wave-overtopping; estuary; juvenile fish; estuarine dependence; Lake Nhlabane; South Africa


(Afr J Aqua Sci: 2001: 26(2): 109-113)