Original Articles

A comparison of the fish communities in nearby permanently open, seasonally open and normally closed estuaries in the South-Western Cape, South Africa

Published in: South African Journal of Marine Science
Volume 8, issue 1, 1989 , pages: 43–55
DOI: 10.2989/02577618909504550
Author(s): B. A. Bennett


Seine-netting for 13 consecutive months in the permanently open Palmiet Estuary, in the seasonally open Kleinmond Estuary, and in the Bot Estuary, which had been closed for three years, yielded 101 000 fish. Seven species complete their entire life cycles in estuaries, 13 breed in the sea and migrate into the estuaries as juveniles, and two were freshwater species. Classification and ordination showed that the structure of the communities changed markedly during heavy freshwater flushing in the Palmiet and Kleinmond estuaries but not in the Bot. This was related to a massive emigration of species and individuals in the former two systems. Spawning by the permanent residents in spring/summer ensures minimal loss of eggs and larvae from the estuaries and allows juveniles to benefit from favourable summer and autumn conditions. Winter spawning by the marine migrants allows juveniles to enter the estuaries in the spring and early summer, after the winter floods but before the estuaries close. Differences in the species composition of the three estuaries are related to differences in the duration of connection between the estuaries and the sea.

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