A COMPARISON OF THE ICHTHYOFAUNAS IN 2 PERMANENTLY OPEN EASTERN CAPE ESTUARIES

The Kowie and Great Fish estuaries are situated less than 30 km apart, yet they diff er considerably in terms of riverine inflow, turbidity, food resources and habitat availability. The ichthyofauna of the two estuaries were sampled using plankton, seine and gill nets. A greater ichthyofaunal richness (R) was recorded in the Kowie estuary and this is attributed to the wider range of habitats and greater degree of mar ine influence in this system. In contrast, all three sampling gears re vealed an approximate 3:1 ratio between fish abundance in the Great Fi sh and Kowie estuaries. The higher abundance of fishes in the Great Fi sh estuary is partly attributed to the large organic and nutrient inpu ts into this system when compared with the Kowie system, and the influ ence of these inputs on estuarine primary and secondary production. In dividual fish species are affected differently by turbid water conditi ons. Indications from this study were that piscivorous fishes (e.g. Li chia amia) which rely mainly on visual foraging methods were adversely affected by the high turbidity conditions within the Great Fish estua ry, whereas piscivores (e.g. Argyrosomus hololepidotus) which rely mai nly on non-visual methods were unaffected. Macrobenthic predators (e.g . Pomadasys commersonnii) and detritivorous fish species (e.g. Mugil c ephalus) also appear to be unaffected by high suspensoid levels and we re usually more abundant in the Great Fish than in the Kowie estuary. The length-frequency distributions of some of the dominant fish specie s occurring in both estuaries are presented.