South American Sea Lion: A brief tale
Tales from the South American seas of snouts, whiskers and flippers. An in-depth account of the Patagonian Sea lion, their behaviour, mating cycles and population, with special reference to threats they face, both human and natural.
The South American Sea lion, commonly known as Patagonian Sea lion or the hair seal, is one of the members of Otariidae family. They are frequently referred to as otariids or pinnipeds, are distinguished by other members of families due to presence of ears. Though the Latin name for this species was under argument for many years, there were two recommended names : Otaria byronia and Otaria flavescens, the latter of which is now used as the official Latin name.
The males differ from females in many aspects including body weight, length and colour. The males are much taller and heavier than females. The males can grow up to300-340 kg in weight and 256 cm in length, whereas, females can weigh up to 144 kg and attain a maximum length of 200 cm. Not only the adults, these difference in size and weight according to gender are recorded in new-borns and juveniles as well. Colour ranges from dull yellow in females to very dark brown in males, while pups are usually black at birth.
The population of the Patagonian Sea lion is scattered along the Atlantic and Pacific shores of South American continent. Several studies have estimated the total population size at different sites. It was recorded to be 22,157 in Southern Argentina and a total of 110,000 at south-western Atlantic coast. The groups or individuals can be commonly seen at the Patagonian coast, Falkland islands and southern islands.
The South American sea lions are not so picky about their prey species. They feed on fishes, squids to crustaceans and sometimes even penguins. The males usually travel more for hunt than the females. They can dive deep down to 30 metre for catching their prey. Mostly they have been observed to make their hunt easy by stealing fishes from large commercial gill nets, although sometimes this routine turns out to be fatally disadvantageous for them. They often get killed for catching fishes from the nets.
South American sea lions are polygynous species; the adult males try and mate with more than one female. During breeding season, male-male competition for mating is prominent. In such cases, large and strong males usually find success in mating with maximum females. Besides opposing other males, substrate, topography and thermoregulatory conditions of the breeding region also plays an important role in male mating behaviour. First season of breeding commences from early December, where several males defend both breeding area and females in oestrus phase. It has been observed that the males who manage to come first at the breeding site had maximum copulations.
Non-territorial males join a separate gathering, known as the “bachelor clubs”. Member from this club are known to pursue some different mating techniques. They may try to make a spot on outer edges of already existing territories or they invade the territories after most of the capable adult males have left the rookeries. Another unique strategy which they adopt is group raiding. This has a huge impact on females as well as the new borns, These raids commonly end up with mother-pups separation, seizing young ones or even death of a new born. This phenomenon is only observed in one other species, the Australian sea lion, making this a rare behaviour in pinnipeds.
The highest number of pups are usually born in January. After spending 2-3 days with their pups, mothers go for a foraging trip which last for maximum 4 days. Mostly, pups are seen playing, sleeping or eating. The lactation period for the newborn pups stay for an approximate of 8-10 months. The mother and pup share a strong bond. Both can remember and identify each other’s smell and sound. Although, the pup mortality rate is very high due to some prominent reasons like splitting up from mother, being abused by adult males or starvation, the mortality rate has been recorded from 2-50%. Killer whales and sharks are the common predators of this species.
The body of the Patagonian Sea lion is well adapted for cold as well as hot weather. Thick layer of fat, called blubber, helps to avoid heat loss whereas the hairless, vascularized large flippers act as a cooling organ. They perform several tricks like waving flippers in air, exposing it to the wind and sometimes urinating on them to control body temperature. However they also use moist surfaces like pebbles or sand and tide-pools to keep their body cool.
Without a doubt, the humans have hunted this species for either commercial or profit purpose. Three main resources were obtained from pinnipeds: oil, meat and fur. But South American sea lions were mainly hunted for oil and sometimes for skin. Even pup’s pelt are used by the garment industry. It is still used to lure southern king crab in Southern Chile.
Not only hunting, but environmental changes also led to a decrease in the population of the Patagonian Sea lion. El Niño was one of the factors which lead to decrease in prey species, changes in reproductive, foraging and maternal behaviour. During El Niño, the onshore trips were shorter whereas time for foraging were longer. But the females were not able to adapt during the 1997-98 El Niño effect due to intense prey scarcity. It led to increase in pups fasting period which in turned caused high mortality rate due to hunger and starvation of the new borns.
Out of all regions, this species faced a steep decrease in population in northern Patagonia. During 1930-60, a huge amount of skin export was done from this region to Argentina (approximately 201 259 from 493 438 skins). In 1946, the population fell to approximately 18,000 from an earlier count of 137,500 in 1938, though a steady increase in population close to 5.7% annually was observed from 1983-2002. However, the population has not recovered in Falkland Islands, although, according to IUCN red list, it comes under least concern category and is still safe.
Read also: Revisiting the moments in the wild
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