Australian Sea Lions, Neophoca cinerea
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Description & Behavior
Australian sea lions, Neophoca cinerea (Péron, 1816), have stocky bodies, large heads and short narrow flippers. Adult males measure between 2-2.5 m in length and weigh 250-300 kg, while adult females measure between 1.3-1.8 m in length and weigh 61-104 kg (a sexually dimorphic species). Apart from size, their sexes are easily identified by coat color. The males are dark brown with mane-like yellow areas on their necks and the tops of their heads. Their females are silver gray to light tan to dark brown on their backs and creamy colored underneath. One adult male was measured diving to a depth of 245 m.
World Range & Habitat
As their name would suggest, Australian sea lions are found only in Australia. They are one of the most endangered pinnipeds in the world with remaining populations estimated at 10,000-12,000 according to the United Nations Environment Program (UNEP). Their habitat range is around the Australian islands between Houtman Abrolhos (28°S, 112°E) to the Pages Islands (34°S, 138°E) on the southern coast near Kangaroo Island.
Wandering Australian sea lions have been spotted near New South Wales, Victoria, Tasmania and Shark Bay in Western Australia.
This is a sedentary species, which is not thought to migrate or move seasonally. Though some movement of adult and subadult males has been observed on the coast of Western Australia, it appears that Australian sea lions tend to stay around their haulouts and breeding sites. Females may move with their pups to other haulout areas to nurse them.
Feeding Behavior (Ecology)
Little is known about the diet of Australian sea lions, but cephalopods, crustaceans, and fish are probably their major prey. There is some suggestion that they occasionally take penguins as well. Research suggests that the females feed in relatively shallow nearshore waters 20-30 km offshore but may also make some use of deeper offshore waters.
Large sharks, particularly great white sharks, are known to prey on Australian sea lions.
Females become sexually mature at 4-6 years, males at 8-9 years. Australian sea lions are known to live for up to 25 years. Australian sea lions haul out and breed on rocks and sandy beaches, mainly on offshore islands. Individuals have been known to wander several kilometers inland though the reasons remain unclear. A long breeding season of about five months means that the males, unable to protect their territory continuously, spend up to four weeks ashore at a time maintaining small female groups, normally containing 4-6 females, and are very aggressive towards each other. The Australian sea lion has a unique breeding cycle amongst the pinniped species, the females giving birth to their pup after a 17.3-17.7 month cycle. A particular female's pupping season occurs in alternate summers and winters or in alternate springs and autumns, and the pupping season for different Australian sea lion colonies takes place at different times.
The females give birth a day or two after arrival and mate about a week later. Their pups are born measuring about 62-68 cm in length and weighing 6.4-7.8 kg with a chocolate brown coat which it molts at 4-6 months to be replaced by the adult coat which is dark brown, apart from an area of blond fur on the head for males and silver-gray/brown on the back and creamy yellow underneath for females. About 10 days after the pup is born its mother starts going to sea to feed, spending about 2 days at sea and about 1.5 days back ashore, until the pup is weaned. The female nurses its pup for 15-18 months but some pups can be nursed for up to 23 months by the quarter of females who do not pup each breeding season. There is quite a high mortality of pups (40-50% in the first two years, 20% of the pup mortality in the first six months) at the breeding grounds due to aggression by both male and female adults.
Conservation Status & Comments
The species was heavily hunted for its hide and oil in the 18th and 19th centuries before which its range extended as far as the islands in Bass Strait. The Australian sea lion is now listed as Rare under South Australian legislation where it has received full legal protection since 1964 and has Special Protected Species status in Western Australia where it has been legally protected since 1892. The species has also been protected under national Australian legislation since 1975. Some small colonies in South Australia are protected by the Great Australian Bight Marine Park which was created in 1996 by the South Australian government and added to in 1998 by the national government.
Evidence is mounting that the size of the Australian sea lion population has leveled off and may be declining, and calls are being made for more intensive research into the species. Recent research has shown unexplained dramatic fluctuations in pup mortality rates which may be endangering the species. The pup mortality rate during the 1999 breeding season at the Dangerous Reef colony in South Australia, for example, was 41%, a record for the colony, and there are concerns that the colony's population is stagnating as a result. It is thought that the most likely cause of the high mortality at Dangerous Reef was infanticide by aggressive adult sea lions, other factors such as food shortages also being a possibility. However no definite cause has yet been found.
Entanglement in fishing nets, particularly shark nets, and crayfish pots is one of the main threats to the species. Concerns have also recently been raised about the siting of fish farms near sea lion haulouts or feeding areas. Some direct shooting of Australian sea lions occurs but the extent of this is unknown and highly illegal. Populations are highly susceptible to disturbance by humans, particularly during the breeding season.
References & Further Research
Seal Conservation Society: Description and status of the Australian Sea Lion
Seals and Sea-Lions - Dept of the Environment and Heritage - Commonwealth of Australia
Australian Sea Lion - Australian Museum
THE PINNIPEDS: SEALS, SEA LIONS, AND WALRUSES - Marine Mammal Center
Australian Sealion Fact Sheet - Australasian Regional Association of Zoological Parks and Aquaria
Research Neophoca cinerea » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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