South American sea lions are stocky, heavy-bodied otariids that are strongly sexually dimorphic. In both sexes the muzzle is wide, short, and blunt. The nose is large and slightly upturned in females, and even more so in adult males. The lower jaw is wide and deep in both sexes. In adult males it juts somewhat forward, and is also accentuated by the longer hair of the mane. The ear pinnae are small and lie close to the side of the head; they are inconspicuous, particularly in adult males.
Adult males are unmistakable. They have a mane of long, coarse, erectile guard hairs, extending from forehead and chin to shoulders and mid-chest. The neck, head, jaws, and canine teeth are much larger than those of females. The large head, great bulk of the neck and shoulders, and thick mane make the front of the body appear very large and wide, despite the fact that the hindquarters are also wide and robust.
Adult females and subadults of both sexes do not have a mane. Their pelage is predominantly yellowish gold to tan. They are not all uniformly colored, but can be patterned with areas of slightly different hues. Most males darken with age, becoming brownish orange, although the mane and under parts frequently remain lighter. Males can have a darker face, giving them a slightly masked appearance. Some males remain the pale color of females and subadults throughout their lives.
Pups are born black above and paler below, often with grayish orange tones on the undersides. Pups undergo their first molt approximately one month after birth, becoming dark brown. This color fades during the rest of the first year to a pale tan to light brown, with paler areas in the face.
The fore flippers have a sparse short fur that extends beyond the wrist onto the middle of the dorsal surface of the flipper in a “V” pattern that does not reach the rounded tip. The rest of the dorsal surface, and the palms of both fore flippers are covered with a hairless black leathery skin. The first digit is the longest, widest and thickest, and curves posteriorly, giving the flipper a swept back look. Digits 2-4 are successively shorter. There is a small opening in the skin at the end of each digit for a claw that is usually reduced to a vestigial nodule, and rarely emerges above the skin. The claw openings are set back from the free edge of the flippers by cartilaginous rods that extend the length of each digit, and expand the size of the flippers. The hind flippers also have cartilaginous rods that extend the length of each toe. The bones of the three central toes terminate at the position of the small nails that emerge through the skin on the dorsal surface, set back from the end of the flipper. The first and fifth toes are longer than the three middle toes, and the first toe, or hallux, is longer and wider than the fifth toe. The hind flippers have short hair covering part of the proximal end of the flipper, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin.
Adult males reach 2.6 m in length and weights of 300 to 350 kg; females reach 2 m and 144 kg. At birth, pups are 11-15 kg and 75-85 cm long.
The dental formula is I 3/2, C 1/1, PC 6/5.
Can be Confused With
South American sea lions share most of their range with South American fur seals. Wandering South American sea lions could occur within the range of Juan Fernandez and Galapagos fur seals, or vice versa. Antarctic, and sub-Antarctic fur seals occur as vagrants on the coast of South America.
South American sea lions are heavy-bodied animals with proportionately large heads and flippers, and are stockier and more muscular looking than similar length fur seals of any species. All fur seals have longer fur over the entire body and look shaggy when wet. The muzzle of fur seals is thinner and tapers to a pointed end, and the proportionately large eyes and long ear pinnae are more conspicuous. Fur seals are brown to dark brown, and darker than most South American sea lions of similar-size, and have proportionately smaller flippers.
Galapagos sea lions are smaller overall and slimmer in build, with a much smaller head, tapering and narrower muzzle, with a proportionately smaller lower jaw, and a small nose that is not turned up at the end. Coloration in smaller animals is similar, but bulls of each species are unmistakable in color and secondary sexual characteristics.
South American sea lions are widely–distributed, occurring more or less continuously from northern Peru south to Cape Horn, and north up the east coast of the continent to southern Brazil, including the Falkland Islands. They are primarily a coastal species, found in waters over the continental shelf and slope, occurring less frequently in deeper waters. South American sea lions venture into fresh water and around tidewater glaciers and up rivers. Vagrants have been found as far north as 13°S, near Bahia Brazil, and in the Galapagos Archipelago.
Ecology and Behavior
South American sea lions are considered non-migratory, although some may wander long distances away from rookeries during the non-breeding season, and some southerly locations such as the Falkland Islands are largely abandoned during the winter. However, most rookeries are continuously occupied by at least some animals, and the species has been described as sedentary.
They are a highly polygynous species with various strategies employed by males and females during the breeding season that are driven by substrate and terrain at the rookery, and thermoregulatory requirements imposed by weather conditions at the site. Adult males tend to establish territories through vocalizing, posturing, and fighting, when rookeries provide shade, have tidal pools that can be used for cooling, or funnel interior areas through narrow beaches between rocks or ledges to the sea. At more homogeneous locations with long shorelines, male strategy changes to focus on identifying, defending, and controlling individual cows in estrous, wherever they are found. Bulls actively and aggressively work to keep estrous cows close by grabbing, dragging, and throwing them back inland, away from the shoreline.
The start of the breeding season varies somewhat by location and latitude, with pups being born slightly earlier at more southern rookeries. At most sites, both sexes arrive in mid-December with peak numbers of males ashore just after mid-January and peak numbers of females ashore from mid to late January. Females give birth 2-3 days after arrival, and pups are born from mid-December to early February with a peak in mid-January, coinciding with the timing of peak numbers of females ashore. Estrous occurs 6 days after parturition, and females make their first foraging trip 2-3 days after estrous. From this point on, a cycle of foraging and pup attendance starts and lasts until pups are weaned at 8-10 months old. As is the case for many sea lions, it is not unusual for females to continue to care for yearlings. Pups gather in large pods on the rookeries while waiting for their mothers to return from 1-4 day long foraging trips. Females usually stay ashore for 2 days between trips.
At sea, South American sea lions frequently raft alone or in small to large groups. They have been reported in association with feeding cetaceans and seabirds. The mean depth of lactating female foraging dives is about 61 m and the mean duration is just over 3 minutes. The maximum depth recorded for a dive is 175 m and duration 7.7 minutes. Two tagged adult males foraged on the continental shelf prior to the onset of breeding, making 5–6 day trips that covered an average of 600 km before they returned to land to haul–out. Dive depth and length are unknown for these and all males, but the animals spent about 90% of their time in water depths of 50–100 m.
Predators include killer whales, sharks and leopard seals, and possibly the puma. At one now-famous rookery, killer whales are known to surf in on waves, partially beaching themselves while grabbing predominantly young sea lions off the shoreline. Puma tracks were observed on a rookery in Patagonia, and remains of sea lions were found in a cave used by a puma in the area.
Feeding and Prey
South American sea lions are opportunistic feeders, taking a wide variety of prey that varies by location. Their diet includes many species of benthic and pelagic fishes. Important prey species include South Pacific hake, herring, elephant fish, Peruvian anchovy, grenadier fish, South American pilchard, cusk–eels, and butterfish. Invertebrates taken include lobster krill, squid, octopus, jellyfish, and marine snails.
A small percentage of adult male South American sea lions regularly prey on South American fur seals, although many that pass by colonies investigate the nearby waters and may attempt to capture a fur seal. Adult male sea lions hunt alone and focus their attacks on fur seal pups and juveniles, which are consumed when caught. About 17% of attacks are successful, but success varies widely between individual males. Subadult males also attack fur seals, but tend to abduct fur seals to serve as female sea lion substitutes, herding them and attempting to mate with them, usually killing them in the process. Female and juvenile sea lions have not been recorded to hunt fur seals. Sea lions have been observed killing young southern elephant seals in the Falkland Islands. They are also known to take several species of penguins, but the importance of penguins in the diet is unknown.
Threats and Status
The total population is estimated to be 200,000 to 300,000. South American sea lions were hunted by native people of South America for thousands of years, and were taken by Europeans as early as the 16th century for food, oil and hides. Significant commercial harvests occurred in several countries and sea lion numbers were drastically reduced in the last several hundred years. Most populations are currently recovering from past intensive harvests. Sea lions are taken in Chile for use as bait in a crab fishery, and poached or taken incidentally in fishing and fish farming operations, and intentionally for food in unknown numbers throughout their range. Intensive trawl fishing in the coastal waters of southern South America has been implicated in a severe decline of sea lions in the Falkland Islands, where the population has fallen from 30,000 in the 1960s to approximately 15,000 in the 1980s, and possibly to as low as 3,000 in the 1990s.
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