New Zealand fur seals, Arctocephalus forsteri, breed in densely packed colonies where males hold exclusive territories. Both sexes overheat while on land and use shade and pools of water for cooling. In addition, females are aggressive towards one another and rarely tolerate neighbours closer than 1 m away. At a New Zealand colony of this species, agonistic interactions among females occurred most often in areas used for thermoregulation: shaded rock substrate and pools of water. Fewest interactions occurred in sunny, dry areas. These findings suggest that females are competing for a limited resource, which could limit harem size.