Spatial and temporal heterogeneity of growth and mortality of Mytilus edulis in cultured settlements from Kandalaksha Bay of the White Sea have been studied from an analysis of annual length/frequency distributions. It is shown that the values of annual length increment of mussels and their elimination are a function of their initial length and population density. A model suitable for predicting annual changes in mean length and density of mussels on artificial substrata has been constructed on the basis of multiple regression equations. The use of the model in predicting yield is discussed.