These sea lions have been found in estuaries and freshwater systems as well. Natural History There is significant sexual dimorphism in both size and body shape. South American sea lion males average 260 cm in length and weigh approximately 300 kg. They are the most lion like of all the sea lions with a massive neck, broad head and upturned muzzle. Females average 200 cm and weigh 150 kg.
Males are dark brown to brownish orange, and darken with age.
Their manes and undersides may be lighter and their faces may be darker. The female sea lions and subadults are yellow to brownish orange and the colour may be patterned and have different hues or tints. Pups are black above and greyish orange below. They moult to dark brown at about 4 weeks of age. Females reach sexual maturity at about 4 years and males one or two years later.