An Estimation of the Mortality Rates in a Population of Tilapia esculenta Graham (Pisces, Cichlidae) in Lake Victoria, East Africa

Abstract

In the commercial fisheries of the great lakes of Central Africa the nylon gill net is the most widespread type of gear in use at present. Recent increases in fishing effort are believed to have had a marked effect upon the abundance of some species and this paper describes a method of estimating the fishing mortality from a fishery of this type. The method is demonstrated in its application to a population of Tilapia esculenta in Lake Victoria. In particular the data from the gill net fishery are combined with the known selectivity of the gear to distinguish between fishing mortality and trends in natural loss from the population with increasing age of the fish. The study also shows that the population dynamics of a tropical fish species are amenable to conventional techniques of analysis.