The inshore fisheries on the Zimbabwean and Zambian side of Lake Kariba have ever since the creation of the lake undergone different management regimes. The Zimbabwean side is, compared to the Zambian, much more regulated and enforced resulting in a fishing pressure and fishing pattern which has not changed much over time and where the fish stocks are only moderately exploited. In contrast, the Zambian inshore fishery, with virtually no enforcement of regulations, has experienced a much higher fishing intensity and a changed fishing pattern towards increasingly smaller mesh sizes resulting in a higher exploitation level and reduced stock sizes. In both countries effort has been fluctuating over time. However, in Zimbabwe the effort in general has shown a decreasing trend while CPUE has increased, whereas in Zambia effort generally has increased with a corresponding decreasing trend in CPUE. The overall fishing effort, in terms of number of nets, is about seven times higher in Zambia than in Zimbabwe, while the average experimental catch rates are seven times lower. However, the artisanal catch rates are not very different on both sides of the lake (1.8 and 2.8 kg/net in Zambia and Zimbabwe respectively). This would indicate the Zambian fishers somehow are able to maintain the catch efficiency by decreasing the mesh sizes (Figure 11) and, probably through increased use of fish driving.
Nevertheless, there are no indications of biological overexploitation in the Zambian inshore fishery in terms of reduced total yields or changed fish communities. This leads to the conclusion that the Zimbabwean inshore fishery is underutilized.
Lake Kariba, as a man-made artificial environment, is slowly but constantly changing in terms of biological species succession indicating that it has not yet reached its final maturity stage 40 years after its creation. Both sides of the lake appear to undergo the same trends in diversity development, irrespective of fishing pressure and fishing pattern. The slopes of the biomass-size distributions are equal on both sides of the lake, although with significantly different intercepts. This indicates that the relatively high fishing pressure on the Zambian side does not have any negative impact on the community structure, only that the stock sizes are reduced presumably due to fishing.
The seasonal inputs of nutrients (through the river and through inundation of shores) into the system has a significant effect on the regenerative capacity of the stocks, indicating that Lake Kariba is a naturally fluctuating environment where effort limitations has limited effects on the conservation of stock size levels. In such a system the notion of sustainable long-term yields becomes very difficult to define. Furthermore, there are indications that with increased fishing pressure the relative effect of the environmental changes become relatively more important than the fishing mortality resulting in an increased variability of the catch rates but reflecting the high degree of resilience in the ecosystem. In such a situation, the fishery must adapt to the natural fluctuations by taking advantage of the good flood years, and, by a diversified economy, be able to survive the lean periods. Management regulations such as limited entry and restricted mesh sizes as in Zimbabwe would result in a higher stability for the individual fisherman, but on the other hand in a severe underutilization of the potential yields.
