Reviews in Fish Biology and Fisheries 9: 151–186, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Ichthyofaunal assemblages in estuaries: A South African case study
Alan K. Whitﬁeld
J.L.B. Smith Institute of Ichthyology, Private Bag 1015, Grahamstown 6140, South Africa (E-mail: a.whitﬁeld@
Accepted 2 December 1998
Abstract Page 151
Life-history patterns 152
Estuary association analysis 155
Early life-history stages 155
Factors inﬂuencing ﬁsh assemblages 161
Zoogeography and seasonality
Catchment and estuary size
Fish biomass and resource utilization 173
Conservation of ﬁshes in estuaries 177
This review places the life-history styles of ﬁshes associated with South African estuaries in a global context
and presents a classiﬁcation system incorporating all the major life-history categories for estuary-associated ﬁsh
species around the world. In addition, it documents the early life histories of the major ﬁsh groups in South
African estuaries, with particular emphasis on the differing modes of estuarine utilization by marine, estuarine and
This review details factors inﬂuencing the ichthyofaunal community structure in South African estuaries. The
availability of ﬁsh for recruitment into an estuary depends primarily upon the distributional range of euryhaline
marine and estuarine species, with tropical and temperate taxa showing marked abundance trends. Within a
particular biogeographic region, however, estuarine type and prevailing salinity regime have a major inﬂuence
on the detailed ichthyofaunal structure that develops. There is an increasing preponderance of marine ﬁsh taxa
when moving from a freshwater-dominated towards a seawater-dominated type of system, and a decline in species
diversity between subtropical estuaries in the north-east and cool temperate systems in the south-west. Similar
declines in ﬁsh species diversity between tropical and temperate estuaries in other parts of the world are highlighted.
Fish assemblages in estuaries adjust constantly in response to changing seasons, salinities, turbidities, etc.
Despite persistent ﬂuctuations in both the biotic and abiotic environment, the basic ichthyofaunal structure appears
to have an underlying stability and to be predictable in terms of the response of individual species to speciﬁc
conditions. This stability seems to be governed by factors such as the dominance of eurytopic taxa within estuarine
assemblages and the robust nature of food webs within these systems. The predictability arises from factors such