The present study was undertaken during the summers of 1974/75 and 1975/76. Beaches were classified according to their topography and structure, and colony types were classified according to age and sex composition during the breeding season peak haul-out. Breeding success was measured by the total number of pups born. All available beaches were occupied during the breeding season, breeders predominating on the windward west coast and nonbreeders on the leeward east coast. Principal factors influencing the distribution of breeding fur seals were the topography and physical nature of the beaches, ambient temperatures and solar radiation, sea condition, and exposure to wind and sea spray. The resultant distribution pattern is ascribed to a behavioural thermoregulatory response in A. tropicalis so as to reduce exogenous heat-loading during the summer breeding season.