Every 4-5 years it’s necessary to spring clean the dams to clear them of carp and catfish. These fish make their way into the dams from the Breede River through the canal system. When they get to the dam they stir up the mud and silt at the bottom which clogs the sand filters of the irrigation pumps. Even though the filters are regularly back-washed to clean them, it still results in a annual 5% reduction in flow – which means 5% of the electricity used to pump the water is being wasted or c.R18K a year goes down the plug! As well as blocking up the irrigation system the carp change the habitat quality for indigenous fish adapted for hunting or feeding in clearer waters, and destroy vegetation that is a breeding ground to most fish sharing the ecosystem, so many conservationists view them as pests.
Carp are an alien species in South Africa and are originally from Asia. The Romans ‘farmed’ carp in South Central Europe but the spread of domesticated carp as ‘food fish’ was by monks between the 13th and 16th centuries. They were introduced in South Africa by European settlers for recreational fishing and as a source of cheap protein but, according to Dr Brian van Wilgen, carp are eliminating native fish and causing water quality issues. Like most invasive alien species, carp are hardy and can tolerate a wide range of conditions, thriving in dams and large murky rivers. They out compete native fauna and it is estimated that 60% of endemic freshwater fish are under threat.
First the level of the dam was dropped by opening the valves allowing water to escape straight back into the Breede River. Then Willem Jordaan and his team arrived to catch the fish in their nets. The advantage of this method is that the water quality isn’t affected and only carp and catfish are removed – any indigenous fish caught in the nets, like Gilchristella Aestuaria and blue kurper (tilapia), are immediately returned to the water.
The carp that are removed from the dam go on to be sold by Willem Jordaan, providing a cheap source of healthy protein – they’re particularly popular with immigrants from Nigeria, Zimbabwe and northern Europe where freshwater fish is commonly eaten. An increasing number of locals are also starting to sample the fish having seen how it can be prepared and cooked.
The top dam was then refilled and a floating suction pipe was fitted to relay water to the bottom dam. The pipe floats on the top of the water and has 8mm holes in it to prevent carp and other bottom feeders from making their way into the bottom dam where in future we hope to stock Berg-Breede River Whitefish which are very threatened.