Laboratorio de Mamíferos
Marinos
Especies
Dusky dolphin - SOUTHERN RIGHT WHALE - South American sea lion - South american fur seal
© Ilustration by Pieter Folkens in Encyclopedia of Marine Mammals 3ra Edition
South American sea lion
Scientific name: Otaria flavescens
It is a sexually dimorphic species. Males typically have a mane, great development of neck muscles, blunt snout, and reach 2.6 m (8.5 ft) long and 350 kg (770 lb). Females lack a mane, they have a slender body, and are about 2 m (6.5 ft) long and 150 kg (330 lb). Fur color may be variable, from dark brown to yellowish light brown. Calves have a dark black fur since they are born until they are two months old.
It is typically colonial and polygynous, with an annual cycle divide in a short reproductive phase on land; and a phase in the ocean alternating foraging trips and times of rest on shore. Animals perform seasonal displacements among several haul-outs, in a cyclic manner from one year to the other. Breeding season is from December to February, and the peak of both reproductive individuals on land and births is found during mid-january.
Depending on the substrate features and density of the colonies, males exhibit various types of mating systems, including female defense, resources or territory defense, lek-like mating systems (or direct competition for dominant status or favorable position within male aggregations), and grouping of subadults males for stealing females. Mature females give birth to an only pup each season within 3-5 days after arriving to the colony after a year-long gestation period. Pup at birth may weigh between 12 and 15 kg (26 - 33 lb). Lactating may last up to 8 to 12 months, although females frequently breast feed a newly born and a one-year old pup (previous season pup). Females reach their sexual maturity at 4-5 years. Males are physiologically mature t 4-6 years, but it is not until they are 9 years old that they can defend a territory and protect a harem. Females live longer than males, with maximum life spans of 22 and 19 years, respectively. Survival rate is also higher in females, with females of each specific age surviving more than males of all ages.
Among its predators we find the Orca (Orcinus orca), several species of sharks, and possibly leopard seal (Hydrurga leptonix) and puma (Puma concolor).
Aerial photograph of a colony in Northern Patagonia, Argentina. (Photo: Dario Podestá)
Map showing the worldwide distribution of South American sea lion.
It is widely distributed in South America. Colonies for this species are found from Zorritos, Peru (4°S) on the Pacific Ocean, to Torres, Brazil (29°S) on the Atlantic Ocean. World population is estimated in no less than 445,000 individuals. This species was intensively hunted for commercial exploitation during the late XIX and early XX century. Despite being an abundant species, current abundance in the Atlantic Ocean is far below the estimated numbers for times previous to exploitation. Tendencies after the end of commercial hunting vary depending on the geographic area. Stocks in Uruguay and Southern Chile continue to reduce; in center Chile they are stable; and stocks in Falklands (Malvinas) Islands, Perú, and northern Chile. Are recovering slowly. Groups inhabiting Patagonia in Argentina are currently in recovery but showing variable rates. The recovery process was accompanied by a spatial recolonization, changing colonies social structure and survival of certain social classes.
Molecular studies revealed a significative genetic differentiation among colonies in the Atlantic and Pacific Oceans. In the Atlantic, females show distinct subpopulations geographically structured: Uruguay, Patagonia, and Malvinas Islands, whilst males maintain a genetic flow among regions. On the Patagonian coast, distinct females’ populations were detected among colonies in northern and center Patagonia, Santa Cruz, and Malvinas Islands. In a smaller scaler (colonies distributed within ~ 250 km in northern Patagonia) population genetic structure is weak.
South American sea lions are opportunistic and generalist, with plasticity to adapt and modify their feeding behavior, taking advantage of a wide range of prey along its distribution including benthic and demersal-pelagic fish and invertebrates. Adult and subadult males have a larger action ratio than females and juveniles. Many prey species are of commercial importance in fisheries generating direct and indirect interactions. There is an overlap in resources and /or utilized areas between South American sea lions and artisanal and industrial fisheries. This generates bycatch in gill nets, seine nets and trawling fisheries in many areas. These direct interactions cause mortality. Although historical estimations indicate that mortality values are not high enough to affect population, there is not an updated evaluation of the real problem. Moreover, fisheries affect sea lions indirectly by competence for resources.
On the other side, South American sea lions are exploited as touristic resource. Even though tourism activities offer a non-lethal alternative and result in an outreach tool, many of the new haul-out areas (arisen from population recovery) are outside a protected area system. Protection is only on land because marine protected areas are scarce. Recently snorkeling activities have been developed with sea lions in Patagonia, generating several behaviors depending on the time of the season. Thus, they require constant monitoring.
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Photographs of commercial hunting in the late 19th and early 20th centuries.
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