This study examines the effect of a clumped, non-defendable and abundant year-round food resource (Cape fur seals) for black-backed jackal Canis mesomelas social structure and spatial organization at Cape Cross Seal Reserve and the National West Coast Recreation Area in Namibia during the jackals' denning period in 2004 and 2005. Geo-referenced observations of behaviour and space-use were used to test for territoriality, and to assess commuting distances, territory size, group size and within-territory density on the Namibian coast. Jackals displayed behaviour indicative of territoriality to within 50 m of the fur seal colony. In accordance with optimal foraging theory, jackals commuted between 0.45 and 20.03 km from their territory (low prey availability) to the seal colony (high prey availability). The observed within-population variation in group size (two to eight adults), territory size (0.20–11.11 km²) and within-territory density (0.31–9.80 jackals km²) was unprecedented and strongly associated with distance from the food resource. Group and territory size increased, while within-territory density declined with increasing distance from the fur seal colony. We discuss the relative importance of the food resource and other factors in determining jackal social and spatial organization. Keywords: Canis mesomelas, black-backed jackal, resource distribution, territoriality, group size, commuter system, Namibia.