Sea Lions: Overview

Abstract

Sea lions are members of the family Otariidae. There are presently seven sea lion species in five genera. They originated in the Northeast Pacific region, sharing a common ancestor with fur seals. Although the fossil record for sea lions is poor, it appears they crossed into the Southern Hemisphere about 3 million years ago. Sea lions do tend to be larger than fur seals, with both groups exhibiting substantial differences in body mass, and smaller differences in body length, between males and females, a phenomenon known as sexual dimorphism. The ability to dive and stay underwater is an important characteristic for all marine mammals, including sea lions. Although large lung volume is important for diving animals, the lung volume for sea lions is equally proportional to their body size as to other marine mammals and even terrestrial mammals. They follow a lifestyle typical to that of all the otariids, with some characteristics common to all seals. They are long-lived, have delayed sexual maturation, and have physical and social sexual bimaturation, with males maturing more slowly than females. The status of sea lion populations is variable. The Japanese sea lion has not been sighted since the 1970s and is now considered extinct. According to the International Union for Conservation of Nature (IUCN), three species—the California, Australian, and southern sea lions—are currently considered as being at low risk of extinction. The sea lion species for which there is greatest concern at present and is listed as endangered and at high risk of extinction by the IUCN is the Steller sea lion.