Implications of a changing climate on the Kapenta fish stocks of Lake Kariba, Zimbabwe

Abstract

The influence of climatic variables (rainfall, temperature and evaporation rates) and lake water levels on the stocks of the sardine fish species Limnothrissa miodon (Boulenger), commonly known as Kapenta in Lake Kariba, was investigated. Secondary data of the climatic variables, water levels and fish catches recorded from 1963 to 2008 were analysed to determine their trends over time as well as the relationships among them. The analyses showed that rainfall is decreasing at a rate of 0.63 mm per year around Lake Kariba, while evaporation rates have increased by 31% at an average rate of 2.77mmper year since 1963. The temperatures around the Kariba area have been rising since 1964; with the maximum range increasing at a faster rate than the minimum temperatures. Kapenta fish production has decreased significantly (R2=0.85, P ≤ 0.05) since 1974 at an average rate of 24.19 metric tons per year. This pattern of decrease was also observed in the artisanal fish catches that have declined at an average rate of 37.26 metric tons per year between 1974 and 2003. All the climatic factors as well as the water levels could explain variations in the Kapenta fish catches with the water levels exerting the greatest influence (R2 = 0.84, P 0.05); followed by maximum temperature (R2 = 0.72, P ≤ 0.05), evaporation and rainfall. In turn, water levels are largely influenced by climate with temperature and rainfall explaining a significant portion of the variation in the water levels (R2 = 0.99, and R2 = 0.93, P ≤ 0.05) in that order. This suggests that both climate (maximum temperature in particular) and nutrients, which are influenced by water levels, are the primary determinants of Lake Kariba’s Kapenta production. Concerning are the possibilities that a changing climate in and around the lake may continue to adversely affect water levels, the stratification cycle, nutrient fluxes and the Kapenta fish production in the lake.