An assessment of the nkacha net fishery of Lake Malombe, Malawi

Since the early 1990s the fishery of Lake Malombe, Malawi, has been dominated by haplochromine cichlids which are mainly harvested with a small-scale purse seine called an nkacha net. The annual landings from the fishery declined from 9 500 tons in 1990 to less than 4 000 tons in 2001. The catch rate, species- and size-selectivity of nkacha nets were assessed between April 2000 and March 2001. The catch per unit effort was 164.5 ± 8.4kg trip-1. While a total of 56 taxa were identified in the catch, five cichlid species, Copadichromis chrysonotus, Copadichromis virginalis, Lethrinops turneri, Otopharynx argyrosoma sp. 'red' and Otopharynx tetrastigma contributed more than 60% to the total catch composition by weight. Differences in the mean length-at-50%-selectivity (φ) into nkacha nets with mesh sizes ranging from 6mm to 19mm were marginal. For all five species, the length-at-50%-selectivity into the fishery was less than the length at maturity. Comparisons with previous work show that C. virginalis, L. turneri and O. argyrosoma sp. 'red' declined in abundance in nkacha net catches between 1991 and 2000. The fishery therefore tends towards both growth and recruitment overfishing.