The South American sea lion (Otaria flavescens, formerly Otaria byronia), also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the western and southeastern coasts of South America. It is the only member of the genus Otaria. The species is highly sexually dimorphic. Males have a large head and prominent mane. They mainly feed on fish and cephalopods and haul out on sand, gravel, rocky, or pebble beaches. Breeding males typically defend both territories and individual females, though this can vary. Less dominant males may try to achieve success by causing chaos in the group. The overall population of the species is considered stable, estimated at 265,000 animals.
Naming
The South American sea lion was classified as Otaria flavescens by George Shaw in 1800 and as Otaria byronia by Henri Marie Ducrotay de Blainville in 1820. The two nomenclatures were historically used interchangeably, but O. flavescens has become the preferred name. The species is also known by the common name "southern sea lion", although it is not preferred since the Australian sea lion and New Zealand sea lion also range in the Southern Hemisphere. Locally, it is known by several names, including león marino (sea lion) and lobo marino (sea wolf).
Adult males have large heads with short, upturned snouts and long manes which reach the shoulders. However, the movement ecology of South American sea lions remains poorly understood, although biologging studies in recent years have advanced our understanding of their at-sea movements at some breeding locations. There is no evidence of a winter migration of sea lions from the Falkland Islands.
South American sea lions breed on beaches made of sand, gravel, rocks, or pebbles. They can also be seen on flat, rocky cliffs with tidepools. Sea lion colonies tend to be small and scattered, especially on rocky beaches. The colonies make spaces between each individual when the weather is warm and sunny. They have even been observed preying on penguins, pelicans, and female and young South American fur seals. South American sea lions may forage at the ocean floor for slow-moving prey or hunt schooling prey in groups, depending on the area. When captured, the prey is shaken violently and torn apart. The sea lions themselves are preyed on by orcas and sharks; at Peninsula Valdes, orcas will beach themselves and grab sea lions near shore.
thumb|275px|right|Male with [[Harem (zoology)|harem]]
During the breeding season, males that fail to secure territories and harems, most often subadults, will cause group raids in an attempt to change the status quo and gain access to the females. Group raids are more common on sandy beaches than rocky ones. These raids cause chaos in the breeding harems, often splitting mothers from their young. The resident males try to fight off the raiders and keep all the females in their territorial boundaries. Raiders are often unsuccessful in securing a female, but some are able to capture some females or even stay in the breeding area with one or more females. Sometimes, an invading male abducts pups, possibly as an attempt to control the females. They also take pups as substitutes for mature females. Subadults herd their captured pups and prevent them from escaping, much like adult males do to females. A pup may be mounted by its abductor, but intromission does not occur. While abducting pups does not give males immediate reproductive benefits, these males may gain experience in controlling females. Pups are sometimes severely injured or killed during abductions.
Despite being mostly a harem-territorial species, one population in Peru has been recorded having a lek-like breeding system. Here, with its longer ratio of males in comparison to females, the males cluster together and display and try to attract females while allowing them to move freely. The warmer climate also makes the females move constantly to the water, further making the traditional mating system difficult to maintain. The group raids that exist in temperate populations are virtually non-existent here.
thumb|female and pup
Sea lion mothers remain with their newborn pups for nearly a week before making a routine of taking three-day foraging trips and coming back to nurse the pups. Pups first enter the water at about four weeks and are weaned at about 12 months. This is normally when the mother gives birth to a new pup. Pups gradually spend more time in the nearshore surf and develop swimming skills.
Human interactions
thumb|upright=0.75|Sea lion pup depicted in Moche art
The Moche people of ancient Peru worshipped the sea and its animals. They often depicted South American sea lions in their art. Two statues of this species are the symbol of the city of Mar del Plata.
This species was exploited by Indigenous peoples of South America for millennia and by Europeans around the 16th century. The hunting has since gone down and the species is no longer threatened. The species is protected in most of its range. Numerous reserves and protected areas at rookeries and haul-out sites exist for the sea lions. Despite this, protection regulations are not effectively enforced in much of animals' range. They still are killed due to their habits of stealing fish and damaging fishing nets.