Caprivi & Kavango

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Studying the biology of bream

Studying the biology of bream

Studying the biology of bream

For most of the past year I have been living in a two-man tent on the banks of the Kavango, Kwando and Zambezi Rivers and Lake Liambezi in north-eastern Namibia. Aside from mastering the art of ground level cooking (not easy when you are 6ft 5in) and eating enough bream for a lifetime, I have learnt a tremendous amount about the three rivers and lake, and the fishes therein.

I have been studying the biology of the larger bream (tilapia) species for my MSc at the University of Namibia. The aim of my research, undertaken in collaboration with the South African Institute for Aquatic Biodiversity, is to develop management recommendations for the conservation and sustainable utilisation of the Kavango and Caprivi fisheries. There are no fewer than ten medium to large bream species found throughout the region. Most notable among these are the predatory nembwe and humpback largemouth and the smallmouth three spot and red breast tilapia. As well as being popular angling targets, these species form the backbone of the subsistence and semi-commercial gill net fisheries. The varied environmental conditions present in each of the four major aquatic systems mean that the biology of these species differs between the systems. For example, fish in the smaller Kwando River with its crystal clear waters, similar to those of the Okavango Delta, are generally much smaller than fish in the Zambezi and Kavango Rivers. A good-sized nembwe in the Kwando may be 1.5 kg while in the Zambezi a nembwe of similar age may be over 3 kg. In the Kwando, low nutrient levels mean the fish grow much slower and mature at a smaller size than in the Kavango and Zambezi.

The recently flooded Lake Liambezi has extremely high levels of nutrients and so fish grow very rapidly in the lake. This high level of productivity helps to sustain the large gill net fishery on the lake which harvests between three and five tonnes of mainly three spot and red breast tilapia per day. These variations in life history between systems have implications for fisheries management. With increasing conflict between recreational anglers and local fisherman over the gradual depletion of trophy sized fish and bream stocks in general, especially in the Upper Zambezi, I anticipate my recommendations will allow managers to take decisions toward sustainably managing the fisheries of the Kavango and Caprivi for recreational anglers and local fisherman alike.

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