Some reach the South Island mainland. Females are approximately 200 cm and weigh 160 kg.
Adult males are dark blackish brown with a well developed dark mane.
Adult females and subadults are silver grey on their backs and pale yellow or creamy white on their bellies and above the ears, eyes and down the sides of their muzzles. These markings extend down the nose and over the top of their heads to the nape of the neck. At about 2 months the pups moult to the subadult colouring. Females are sexually mature at 3-4 years and males at 5. The bulls arrive on the rookeries in late October and early November and defend territories that move with them.