River flow and fish abundance in a South African estuary

Abstract

The ichthyofauna of the Thukela Estuary, a small (55 ha), shallow (<1_5 m) system on the KwaZulu-Natal coast (mean annual river runoff of 3865_106m3, from a large catchment of29 000km2, is seasonal: peak inputs occurring between November and March), was dominated by the juveniles of marine taxa that used the estuary as a nursery area. A striking feature of the above community was the decline in fish abundance with increasing river input, with flow values >100m3 s_1 leading to increased loss of species from the system. This decline was linked to the lack of saline intrusion into the estuary and increased freshwater flooding through the system.