Australian sea lions are found on islands offshore of Australia. They range from western Australia to islands in southern Australia. The largest populations are found on Kangaroo Island and Dangerous Reef (near Port Lincoln) in southern Australia. The smallest numbers are found on the west coast of southern Australia and in Western Australia. Some live in Tasmania as well, but these are few in number. They once bred in the Bass Strait, but the entire population was wiped out by the sealing industry. (Tasmania Parks and Wildlife Service, 2000)
Australian sea lions are non-migratory , so they live and breed on sandy beaches near their birth site in relatively large colonies. The greatest distance recorded for a tagged animal has been 300km from its birth site (Jefferson, 1993). During times of tumultuous weather, they will often travel inland to seek shelter in dunes and coastal vegetation (Riedman 1990). Unlike many pinnipeds, Australian sea lions are very capable out of the water, and have been found as far as 9.4 km inland (Nowak, 1999). Many have been found at the tops of cliffs as high as 30 meters, as they are also excellent climbers.
At birth, pups are roughly 60 to 70 cm and weigh approximately 6.5 to 8 kg. Their pelage is initially chocolate brown, but is replaced by adult-like fawn colred fur by the age of two months. Australian sea lions are sexually dimorphism, with a significant difference in the size of females and of males. As an adult, males grow to about 2.5 m and weigh 300 kg. Females grow to a length of about 1.8 m and weigh approximately 105 kg. Females reach sexual maturity at around 3 years of age, whereas males usually do not mature until they are 6 years of age or older. Males darken even further as they mature, and go through a transition phase where they have spots on their chests.
Australian sea lions have a large head with a long, narrow, and tapered muzzle. The skull has a sagittal crest approximately 30 mm in height. Males display a much larger head than females and juveniles, as well as significantly broader shoulders. Their pinnae, or ears, are incredibly small and lie close to the head. Juveniles are a dark brown with a pale crown and a dark facial mask. Subadult males and females display a coat that is fawn to silvery-gray on top and tan to pale yellow on the bottom. Mature males are dark brown with a cream-colored crown and nape, and a paler chest and throat area. (Jefferson, et al., 1993; Nowak, 1999; Ridgway, 1972)
The mating system of this sea lion is polygynous. A male secures a breeding territory on the beach and actively defends it against other males though ritualized posturing and aggressive confrontation. The male leaves his territory to feed in the ocean for a few hours at a time. Upon his return, he may have to battle to regain his territory.
Males keep several females on their territories. If the female strays, the male will aggressively herd her back, sometimes entering another male's territory to do so. (Nowak, 1999)
Males have been seen killing pups, although presumably not their own. Defense of territories may be an indirect mechanism of paternal care for young.
There is some evidence of cooperative breeding (See Behavior) in which females care for pups other than their own. (Nowak, 1999)
Australian sea lions have a breeding cycle of approximately 17.6 months. These non-annual cycles are affected by some unknown factor, not by environmental influence as previously thought (Higgins, 1993). Some females do not produce young in consecutive breeding seasons (Nowak, 1999). Births can occur over a period of 4-6 months in any colony of, making births highly unsynchronized.
When the breeding cycle begins, males copulate with harems of four or five females at a time (Ridgway, 1972). Males also have the ability to herd the females into mating groups, a feature rare in other species of sea lion (Riedman, 1990).
Females enter estrous about 6 days after giving birth, and are mated by the male at this time. There is some debate in the literature about the ensuing gestation period. Pinnipeds typically experience a delay in implantation of about three months, followed by an eight or nine month placentation. Becauseexperiences a much longer interbirth interval, it is clear that this species differs from the typical pinniped pattern. Some investigators think that Australian sea lions experience a longer than average dely in implantation of the blastocyst, amounting to 10-11 months, and a normal length pregnancy (8-9 months). Others think there is a more typical pinniped length delay in implantation (5-6 months) and a longer than average placentation (over 12 months). (Nowak, 1999)
Young are typically weaned just before the birth of subsequent offspring, at 15-18 months. However, females have been seen nursing pups of different ages at the same time. (Nowak, 1999; Ridgway, 1972; Riedman, 1990)
Femalecome to shore about two days before they give birth in order to establish a natal site. After giving birth to a pup, the female will stay at the natal site for approximately 10 days before returning to the sea to forage. She will return to land every couple of days to nurse her young, staying with the pup for about 33 hours at a time. A mother uses both vocal and scent communication to locate and identify her pup.
As pups grow up, they often form small groups and swim in shallow rock pools before they venture into the ocean with their mothers.
Females care for their own young, nursing them until about 26 days before giving birth to their next pup. Some mothers have been seen nursing both a yearling and a newborn pup. There are reports of females being aggressive to pups other than their own, but there are also some reports of females taking care of groups of pups. This makes it difficult to determine how much cooperative care of young there might actually be, although it is clear that some cooperative care occurs. Altricial at birth, pups are able to follow their mothers both on land and into the sea at approximately 3 months of age.
No specific male parental care has been reported for (Nowak, 1999), but by maintaining territories, fathers may protect their offspring from other males of the species.
Information on longevity in this species is not available.
Australian sea lions are among some of the only pinnepeds that display “fostering behavior.” This is a form of altruism, as a female will nurse and protect the young of others at her own expense. In some cases, they will even adopt the young of others if the mother is killed. Some females living in the Seal Bay region have even displayed “babysitting behavior,” where a female will protect an entire group of pups even if they are not her own. When she gets tired, another female takes her place (Riedman, 1990). However, it should be noted that there are also reports of females showing agonistic behavior toward pups that are not their own (Nowak, 1999). It may be speculated that the familial relationship between females affects their behavior toward pups.
Males, on the other hand, are not at all protective of the pups, and will often engage in infanticide. They can sometimes be seen viciously attacking pups, often biting or shaking them to death (Bruemmer, 1994). Males will also sexually harass groups of females, and engage in play behavior with other males. Another behavior members of the species exhibit is the practice of swallowing gastroliths (small stones). It is believed that they do this in order to balance their weight when diving for food (Riedman 1990). (Bruemmer, 1994; Nowak, 1999; Riedman, 1990)
Australian sea lions feed on a small number of fishes (which include whiting, rays, and small sharks), squid, cuttlefish, and fairy penguins (Eudyptula minor). The main diet of (Riedman, 1990)consists of blue-throated wrasse (Notolabrus tetricus) and octopus (Achtel, P., personal communication). They concentrate on shallow-water benthic prey, and usually dive for food at depths no greater than 37 meters (Riedman, 1990).
One of the predators of the Australian sea lion is the great white shark (Carcharodon carcharias), especially near the Dangerous Reef region of the Port Lincoln area (Riedman, 1990). Fishermen also occasionally kill them accidentally by entangling them in their nets (World Conservation Monitoring Centre, 2000). Historically, the population was greatly reduced due to sealing (Jefferson, 1993). (Jefferson, et al., 1993; Riedman, 1990; World Conservation Monitoring Centre, 2000)
This species is probably a component of control on fish and penguin populations.
The beauty and docility of Australian sea lions draws tens of thousands of tourists to Seal Bay on Kangaroo Island every year. (Goldie, 1998)
Fishermen often see them as a nuisance as they rob fishing nets and rock lobster traps. (Jefferson, et al., 1993)
Australian sea lions are fully protected within Australia. They were listed as “rare” in the 1994 IUCN Red List of Threatened Animals. They have been recently removed from this list, and the population has remained stable at around 10,000 animals (World Conservation Monitoring Centre, 2000). Harvesting of this species is not allowed, and a permit is required for research or capture for zoos (Toorn, 1999). (Toorn, 1999; World Conservation Monitoring Centre, 2000)
In the past, there have been times of great fluctuation in the population numbers of Australian sea lions. The main reason suspected for the decrease in numbers was parasites such as hookworm. Other factors such as environmental disturbance, male aggression, human harassment, injuries from fishing gear, and competition for resources with the New Zealand fur seal, may all have played a part in their population decline (Goldie, 1998).
Kara Hoglund (author), University of Wisconsin-Stevens Point, Chris Yahnke (editor), University of Wisconsin-Stevens Point.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
helpers provide assistance in raising young that are not their own
in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats fish
having more than one female as a mate at one time
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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Riedman, M. 1990. The Pinnepeds: Seals, Sea Lions, and Walruses. CA: University of California Press.
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