The relationship of temperature and hydrological factors to catch per unit effort, condition and size of the freshwater sardine, Limnothrissa miodon (Boulenger), in Lake Kariba

The relationships between catch per unit effect (Cpue), condition factor and mean length of the fresh water sardine Limnothrissa miodon and air temperature, as well as three hydrological factors, rainfall, river inflow and the water level in Lake Kariba, were determined by regression and correlation analysis of time series data for the period between 1970 and 1996. The aim was to test the predictive value of the environmental variables and to obtain models that describe the relationships between catches and environmental factors. All environmental variables had a significant relation with Cpue and condition, but the relations of the environmental variables to mean length were weak and mostly insignificant. When using data for the whole time period, the maximum temperature was the best predictor of Cpue. Of the hydrological factors, total river inflow had the highest regression coefficient. The data were split into two Ii-year periods (1975-1985 and 1986-1996) in order to test the predictor models. Except for the Zambezi river inflow variable, estimates of Cpue for 1986-1996 using the 1975-1985 model were not significantly different from the observed Cpue. Cross-correlation showed a 5-7 year half cycle in the trend of catches, temperature and the hydrological factors that may be useful for Cpue forecasts. (C) 2000 Elsevier Science B.V. All rights reserved.