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Table 2. Species composition, abundance and biomass of fish in 10 seine net hauls at Uilkraals Estuary, March
2006.
Species Common name Number per ha kg/ha
Atherina breviceps Silverside 176.7 48.7
Caffrogobius nudiceps Nude goby 6.7 11
Psammogobius knysnaensis Knysna sand goby 13284.2 700.7
Mugil cephalus Flathead mullet 36.7 303.3
Heteromycteris capensis Cape sole 213.3 233.3
Liza dumerilii Groovy mullet 3.3 496.7
Solea bleekeri Blackhand sole 6.7 33.3
Liza richardsonii Harder 3036.7 42492
Rhabdosargus globiceps White stumpnose 110 52.7
Amblyrhynchotes hokenii Evil eye blassop 33.3 70.3
Rhinobatos annulatus Sandshark, guitarfish 20 58020
3.7 Birds
The Uilkraals Estuary has been identified as an important area for waterbirds (Barnes 1996).
On a national scale it is ranked 14 th in terms of waterbird abundance in a conservation priority
analysis study (Turpie 1995). Regionally, it was ranked 11 th out of 65 coastal wetland systems
in the south-western Cape in terms of total bird numbers supported (Ryan et al. 1988). A total
of 48 water-associated bird species have been recorded at the Uilkraals Estuary (Table 3). Of
these, 23 species are piscivorous, 21 are invertebrate-feeding and only four species are
herbivorous.
The estuary has supported large numbers of terns and migratory waders in the past (Summers
et al. 1976, Heydorn & Bickerton 1982, Ryan et al. 1988) and has been recognised as one of the
largest mainland tern roosts in the south-western Cape (Ryan et al. 1988).
Only a few bird counts have been conducted on the estuary, all of which were done in the
summer months (Table 4). Previous counts conducted between 1976 and 1981 showed bird
abundances ranging from 4 864 to 6 755 individuals. The count conducted in 1996 showed a
decrease of over 4 500 individuals compared to the 1981 count. This was due to much lower
numbers of terns being recorded, also on subsequent visits to the estuary in the following few
days. This decrease was probably caused by changes in habitat availability. Increased erosion
and changes in sedimentation and river flow have occurred as a long-term result of the
causeway supporting the bridge built in 1973, and the erection of a rubble embankment
(Barnes 1996), and more recently the decreased flows due to the upstream dam. The number
of invertebrate-feeding waders present at the estuary remained relatively stable (Table 4).
Uilkraals Estuary Situation Assessment
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