The flooding of the Zambezi to form Lake Kariba created a whole new ecosystem, changing a river into a huge lake. Existing river fish were unable to survive in deep water so kept to the shallows, leaving two-thirds of the lake devoid of fish. But the fishery potential of this new resource was obviously considerable, so in the early 1960s research was undertaken to find a suitable fish to introduce. Lake Tanganyika supports a thriving population of pelagic freshwater sardine, Limnothrissa miodon, so attempts were made to introduce this to Kariba. After a slow start the sardine (locally known as kapenta) gradually built up a sufficiently large population from which to start a viable fishing industry. Once this critical mass of fish had been reached by the turn of the decade, populations soared and a wonderful new food resource became available, not to mention a great employment opportunity.
(Photo: Crayfish known as 'yabby' © Paul Murray)
Kapenta fishing is done at night with a specially adapted netting technique. The large-framed scoop net, hinged out from the front of the boat, is lowered into the water. Shoals are lured to the surface using powerful lights, while the net is manoeuvred below them. The lights are then turned off and the fish descend into the net. Once on land the kapenta, which only grow to 6–7cm, are salted and sun-dried to form an extremely important protein-rich addition to the local diet.
A very disturbing discovery has recently been made in Lake Kariba which could have disastrous effects on the local environment and economy. A completely alien species of freshwater crayfish has been found to be breeding in increasingly alarming numbers. It’s a voracious feeder and with no effective predators it’s literally threatening to wipe out Kariba’s entire fish stocks including the kapenta fishing industry on which countless people rely as a source of protein. And as with virtually all alien introductions the wider effect on the local environment can be immense – for instance what will happen to the fish eagles if the fry of their prey species get consumed by crayfish? So what to do? Well this cray is very popular in Australia where it is known as the ‘Yabby’ and is eaten by humans in very large quantities, which is the very reason why it was introduced deliberately into Kariba by some thoughtless person who really should have known better. So now we’re stuck with it the best short term solution is for us to consume them at every opportunity. Try to order them even if they don’t appear on the menu because it’s the duty of every visitor to Zimbabwe to join the locals and do their bit to help eat this delicious terrorist out of existence.