Malawi Fisheries Research Institute, PO Box 27, Monkey Bay, Malawi

Spatial and temporal distribution of some commercially important fish species in the southeast arm of Lake Malawi: A geostatistical analysis

The spatial and temporal distribution of the following fish species; Alticorpus mentale, Buccochromis lepturus, Copadichromis virginalis, Diplotaxodon elongate, and Oreochromis spp. in the southeast arm of Lake Malawi were analysed using bottom trawl catch per unit effort (CPUE) data collected during the annual demersal monitoring surveys of 1995 and 1999. Geostatistical techniques were used to model and estimate the spatial structure of abundance and ordinary kriging was used to predict local abundance. Experimental variograms were calculated and fitted using the spherical variogram model. The results indicate that A. mentale occurs mainly in deep waters of Area C and its distribution has shrunk especially in Area B over the same period. C. virginalis principally occurs along the inshore waters of the southeast arm Density has decreased from 1,100 kg nm-2 in 1995 to 680 kg nm-2 in 1999. D. elongate is widely distributed occurring in offshore waters of the southeast arm from Area A to Area C in relatively high densities. The density has declined from 20,000 kg nm-2 in 1995 to 14,000 kg nm-2 in 1999. Oreochromis spp. occur mainly in Area A and to a smaller extent in shallow inshore waters of Area B. There has been a marked decrease in the distribution range with a corresponding decline in density from 319 kg nm-2 to 26 kg nm-2 in 1999. B. lepturus is evenly distributed in shallow waters of the southeast arm. Its abundance has slightly declined in the northeastern part of Area C and Area A.