The species composition of the prey of the Cape Gannet (Morus capensis) was monitored monthly at colonies at Lambert's Bay and Malgas Island in the southern Benguela system off western South Africa from 1977-78 to 1989. A modified form of the biplot procedure gave a parsimonious, descriptive summary of this time-series. The diet at Malgas Island showed much greater seasonality than at Lambert's Bay. Seasonal variations in the anchovy (Engraulis japonicus) and sardine (Sardinops sagax) components of gannet diet conformed largely to the known distribution of these species. However, the gannet diets demonstrated a previously undocumented presence of adult anchovy off the western Cape, particularly in summer. The contribution of sardines to the diet increased from late 1984 at Malgas Island, and from late 1985 at Lambert's Bay, with corresponding decreases in anchovy and hake (Merluccius spp.) at Malgas Island and anchovy at Lambert's Bay. The occurrence of hake in gannet diets, available as trawler offal throughout the year in deeper waters, seems to be associated with a lack of shoaling fish inshore.