Fish diversity at Zandvlei
Zandvlei is a relatively small estuary - 90ha in extent - and has been disturbed by man's activities for several decades. The vlei still supports an impressive diversity of fish species. These fish can be divided into three broad groups:
Fresh water species
Only one indigenous fresh water species remains in the vlei, the diminutive Cape Galaxias. These fish attain only 70mm in length and do not tolerate high salinity levels. Cape galaxias are a valuable food source for predators such as the Malachite Kingfisher. Five exotic fish species have entered the Zandvlei system, the most familiar of which is the Common carp which originates in Asia. Two introduced exotic predators are to be found, the Catfish and the large mouth bass. The Bass is a very popular angling fish but is rare, being restricted to clear, fresh waters. Together with the Common carp, the Catfish is the largest fresh water fish to be found in the vlei. Both Banded and Mozambique Tilapia were introduced as fodder for the large mouth bass.
Estuaries are valuable nursery areas for a wide range of marine fish species. The adults spawn at sea and the fry recruit to estuaries.
Estuaries are favoured by the fry as there are fewer predators, an abundant food supply and calmer, warmer conditions. Species which utilise Zandvlei as a nursery area (despite the rubble weir) include White stumpnose, White steenbras, Southern mullet and Leervis.
The adults of several species also enter the estuary to feed. Predatory fish such as the Leervis and the elf are regularly recorded in the vlei. Nine species of marine fish were recorded in Zandvlei during 1999.
Estuarine roundherring and Cape sole are considered estuarine species as their entire life cycle is completed within the estuary. Such fish are able to tolerate vast fluctuations in salinity levels.
Due to the fact that Zandvlei is the only functioning estuary on the False Bay coastline, it is essential to conserve and manage it to ensure the improvement and long term functioning of the system.