ORCA
ORGANIZATION FOR RESEARCH AND CONSERVATION OF AQUATIC ANIMALS

 

SPECIES OF PERU

MARINE MAMMALS: SOUTHERN ELEPHANT SEAL

Mirounga leonina

ORDER: CARNIVORA
   
Superfamily:  PINNIPEDIA
   
Family: Phocidae
   
Species: Mirounga leonina
   
Common name: Southern Elephant Seal 

Natural History

Size, Shape & Distinctive Characteristics:

South American sea lions show strong sexual dimorphism. Adult males are around 3m in length and around 350kg in weight. Adult females are noticeably smaller, measuring around 2.2m and weighing around 140kg.

Overall they are large-bodied and robust with bulky torsos. Both sexes have relatively large heads with a short, blunt, upturned snout. Males have a much bigger head, with a square muzzle, pointed nose and a crest across the rear of the skull. Females have more rounded heads and muzzles. The pinnae (ears) are small relative to head size, may be hidden by the fur, and positioned close to the eyes. There are 10 pairs of teeth in the upper jaw and 8 pairs in the lower jaw. The teeth are not all the same shape, with definition between the incisors, canines and molars. Their necks are telescopic.

The fore-flippers are broad and long and used to swim, while the hind-flippers appear short and have no fur. The hind-flippers are used for walking on land, due to the ability to rotate the hips.

Adults have a light-yellow to orange-brown pelage and males are generally darker than females.  The whiskers are the same colour as the coat. Adult males have a well-defined mane of guard hairs from the forehead and chin down to the shoulders, which is lighter than the rest of the pelage. Dominant, alpha males are larger than submissive males, with a more discrete mane.  Female coats appear yellowish and are more uniform in colour. Pups have a black or dark brown natal pelage, allowing them to blend in with the rocks. They moult this pelage after about 3 month and then have a shorter bronze coat that turns into silver at 6 months old, which fades during their first year to a dark brown for males and lighter yellowish brown for females.

Geographical Range & Habitat:

The South American Sea Lion is endemic to the coastal waters around South America and is found in disjointed populations from Zorritos, Peru around to Bahia, Brazil, including the Falklands. They may be vagrant further north up both coasts. The population around Peru is unstable and populations may be resident or transient to an area. They generally breed in the south during the summer and travel northwards in winter and spring.

Behaviour:

South American sea lions aggregate into colonies, with density varying according to topography and temperature. Colonies are more dispersed on rocky coasts and when it is warm and sunny. Rookeries are segregated by age and sex.

Males have individually variable vocalisations used to defend territories and herd females, while females use vocalisations primarily in pup recognition.

Females and juveniles moult in the late summer, early autumn, while in generally males moult slightly later.

When diving, males poke only the nose out of the water to breathe.

Pups are vulnerable to killer whale predation and vampire bats are known to attack them along the coast of Peru and Chile.

Life History:

The lifespan of both males and females it thought to be about 20 years for males, 25 for females. Their reproductive behaviour is polygynous, and males build up harems that are then defended through vocalisations, posturing and sometimes, aggressive physical fights. One male will defend up to 21 females at a time. He will also defend the pups of his females and will fast for the duration of the breeding season.

Around Peru, the breeding season starts in late November and lasts up until early March, with the birthing and nursing season taking place between late December and late March. The whole season is now extending due to climate change and the exact dates are location dependent. Seasons are matched to prey abundance cycles so that pups are born at times when appropriately sized prey are plentiful for them to learn to eat fish.

Reproduction physiology includes a delayed implantation of the fertilized egg for 3 months in this species, with pregnancy lasting 11 months. Sexual dimorphism is shown at birth too, with male pups weighing 13-15kg and measuring 79-83cm, and females, 10-14kg and 73-82cm. After birth the mother stays with her pup for about a week and then returns to the sea for 3-day foraging trips, not ranging far from the colonies, and comes back for 2-day nursing breaks in-between. Pups are born with no teeth and suckle with their tongue rather than their lips. They are born with a diving reflex but can’t swim so the first five months are important learning stages with information transfer from mother to offspring and practice. Pups are weaned at between 6-18 months, at the yearling or earliest juvenile stage, when they can swim and eat by themselves.

Diet & Foraging Behaviour:

The diet of South American sea lions is diverse and includes a wide range of fish, cephalopods, and sometimes invertebrates. These otariids (pinnipeds with ears) forage all day long and may have large foraging ranges.  

Population Status

Abundance:

Populations are variable and unstable throughout the range. Estimates from the 1970s and early 1980s have a population of 20,000 along the coast of Peru, 100,000 in Chile, 50,000 in Argentina and 30,000 in Uruguay. Currently Peru population ranges around 35,000 animals year round.

IUCN Status: -

LEAST CONCERN

They are relatively common in other locations of South America, but in Peru is locally threatened and classified as VULNERABLE, meaning that the threats to the species are consistent enough that could lead into an endangered species.  

Conservation Issues:

Competition with fisheries is one of the most severe threats to sea lion populations. Animals are shot or clubbed by fishermen as a result. Directed harvests of them resumed in Chile in 1976. Coastal development also threatens populations due to loss of habitat. Climate change, such as an increase in the occurrence of El Niño, is also threatening populations due to changes in prey abundance and increased disease transmission.

 



Sources: International Commission for Zoological Nomenclature (ICZN),  Society for Marine Mammalogy (SMM), & Organization for Research and Conservation of Aquatic Animals (ORCA).




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