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3.6 Fish
Estuaries provide an extremely important habitat for fish in southern Africa. The vast majority
of coastal habitat in southern Africa is directly exposed to the open ocean, and as such is
subject to intensive wave action throughout the year (Field & Griffiths 1991). Estuaries in
southern Africa are thus disproportionately important relative to other parts of the world, in
that they constitute the bulk of the sheltered, shallow water inshore habitat in the region.
Juveniles of many marine fish species in southern Africa have adapted to take advantage of
this situation, and have developed the necessary adaptations to enable them to persist in
estuaries for at least part of their life cycles. There are at least 100 species that show a clear
association with estuaries in South Africa (Whitfield 1998). Most of these are juveniles of
marine species that enter estuaries as juveniles, remain there for a year or more before
returning to the marine environment as adults or sub-adults where they spawn, completing
the cycles. Several other species also use estuaries in southern Africa, including some that are
able to complete their entire life cycles in these systems, and a range of salt tolerant
freshwater species and euryhaline marine species. Whitfield (1994) has developed a detailed
classification system of estuary associated fishes in southern Africa. He recognized five major
categories of estuary associated fish species and several subcategories (Table 1).
Table 1. Classification of South African fish fauna according to their dependence on estuaries (Whitfield
1994)
Category
I
Ia
Ib
II
IIa
IIb
IIc
III
IV
V
Description
Truly estuarine species, which breed in southern African estuaries; subdivided as follows:
Resident species which have not been recorded breeding in the freshwater or marine
environment
Resident species which have marine or freshwater breeding populations
Euryhaline marine species which usually breed at sea with the juveniles showing varying
degrees of dependence on southern African estuaries; subdivided as follows:
Juveniles dependant of estuaries as nursery areas
Juveniles occur mainly in estuaries, but are also found at sea
Juveniles occur in estuaries but are more abundant at sea
Marine species which occur in estuaries in small numbers but are not dependant on
these systems
Euryhaline freshwater species that can penetrate estuaries depending on salinity
tolerance. Includes some species which may breed in both freshwater and estuarine
systems
Obligate catadromous species which use estuaries as transit routes between the marine
and freshwater environments
Fish species in categories I, II, and V as defined by Whitfield (1994) are all wholly or largely
dependent on estuaries for their survival and are hence the most important from an estuary
conservation perspective. These species need to receive most attention from a management
perspective.
Uilkraals Estuary Situation Assessment
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