2003.
These fishermen were helping to catch carp and catfish at Zandvlei.
There are 27 indigenous fish species recorded at Zandvlei. 5 exotic species which threaten the diversity of the indigenous species are also present. The Sharp tooth Catfish eats vertually anything that fits into its mouth. The Carp are a real problem as they are bottom feeders and stir up the mud and sediment. The birds such as Kingfishers which hunt by sight through the waters surface are not able to find their food source as a result of the the turbid waters. The mud and silt also adversely effects the tubeworm filter feeders and the aquatic plants which filter the water.
Oreochromis mossambicus Mozambique Tilapia was taken on 19/12/2003 at the Westlake Walkway Pond.
Tilapia sparrmanii Banded Tilapia was taken on 19/12/2003 at the Westlake Walkway Pond.
A mud crab in the Westlake Walkway Pond on 19/12/2003.
WOW!! Look at this. This extract from the Cape Argus – 25th August 2003. The article by John Yeld.
photograph by Tanya Graham
Mike Bailey and Alaistar Graham, SA Angling Team members with a 19.8kg Leervis caught at Zandvlei in 2003. This particular fish was caught and released after being weighed by Alaistar. "There are even bigger ones in the vlei, I've lost a couple of them" he said.
Steve Lamberth ( Scientist and Researcher at Marine and Coastal Management ) informed us at The Zandvlei Trust – Spring Festival 2003, that the commercial value of the Zandvlei estuary, to inshore and marine fisheries is estimated at R4 million per annum.
There has been an overall decline in estuarine dependent species such as White Steenbras, Leervis and Harders in Zandvlei. This is mostly due to infrequent mouth opening events, reduced saltwater intrusion and much lower salinity levels. Steenbras and Leervis are at 23 % and Harders at 51 % of their pristine abundance in Zandvlei.
The system has become much fresher resulting in freshwater fish
being 380 % of their pristine levels. Unfortunately, most of these are alien invasives such as
Carp and Sharptooth Catfish which have almost entirely replaced (out competed or eaten) indigenous species such as the
Cape galaxias from Zandvlei.
(The above information was supplied by Steve Lamberth and are
deductions from previous years of study.)
photograph by Clifford Dorse
Pipe fish.
photograph by Clifford Dorse
Closeup of Pipe fish head.
Management
Clifford Dorse has
been encouraging all fresh water anglers to try and catch and not return
the Carp and Catfish, to reduce their numbers. He monitors the bi – monthly mouth opening and Adele Pretorius has been doing her
2003 practical Student subject on the fish populations of Zandvlei.
To show how quickly systems respond to management, there are water
plants which have nearly been eliminated in one season, due to salt
water intolerance in the Centre Pan in the Nature Reserve. The water
levels are control managed for other reasons; to build up the salts for
small food sources for the different wading birds. Also the Cape Teal
requires a high salinity level for feeding.
