Does climate change really explain changes in the fisheries productivity of Lake Kariba (Zambia-Zimbabwe)?

Abstract

This paper examines the notion that the fish stocks in Lake Kariba may now be suffering from the effects of climate change as air temperatures there have increased by about 2 °C since 1960. The ecosystem of Lake Kariba has changed dramatically since it was created in 1958, and the nutrients released by the collapse of the floating water-fern Salvinia molesta evidently brought about an increase in fisheries productivity that lasted for only a few years. This could account for some of the decreased catches attributed to climate change, although the data from the inshore fishery may be unreliable in any case. There is little evidence that climate change has affected the inshore fish stocks. On the other hand, research data from a fished area in Zambia and a closed area in Zimbabwe clearly reveal the impact of fishing. The catch per unit effort (CPUE) in gill nets decreased steadily in Zambia but the CPUE increased in Zimbabwe until it was around 2.5 times greater than in Zambia. The fishery for the introduced sardine Limnothrissa miodon is influenced by river flow, itself a reflection of the climate in the huge catchment area above the lake, and by the seasonal cycle of stratification. These factors do not explain all the variation in the catch of this species, and its CPUE declined through periods when river flows were both high and low. The impact of fishing is the only factor that can explain this.

Keywords:

• Lake Kariba
• climate change
• inshore fisheries
• pelagic fisheries