DISTRIBUTION PATTERNS OF FISHES IN AN EASTERN CAPE ESTUARY AND RIVER WITH PARTICULAR EMPHASIS ON THE EBB AND FLOW REGION

SUMMARY

Two and a half years of data were collected from the Great Fish River (>1%‰), head(1–4%‰) and estuary (>4%‰) using seine and gill nets to determine the fish species composition within these regions. Euryhaline marine taxa belonging to the families Mugilidae and Sparidae dominated the catch in all three regions. Gilchristella aestuaria was the single most common estuarine resident, and several marine species were captured in freshwater for the first time. The cichlid Oreochromis mossambicus was the most common freshwater species but was only abundant in riverine samples. Catches made with the gill nets and large seine net both indicated that the densities of fish were higher at the head than in either the river or the estuary. Since the highest levels of suspended particulate organic matter in the Great Fish estuary are known to be in the head region, the highest densities of fishes would be expected from the same area. Physical parameters were also measured to ascertain some of the possible factors that may affect the distribution and length frequency of the most common taxa within this system. Salinity was shown to be an important factor affecting the distribution of species within the sampled area, with the domination of each region by curyhaline marine taxa being most pronounced in the estuary and decreasing towards the river.