Australian Sea-lion
Along with fur-seals, sea-lions belong to the eared seal family, or Otariidae. They differ from true seals, or Phocidae, by having external ears, propelling themselves through the water with their front flippers and are more agile on land (as they are capable of "walking" on all four flippers).
Population
The world population of the Australian Sea-lion is about 12,000. Of these 8,500 occur in South Australia and 3,500 in Western Australia. They are one of the rarest seal species in the world.
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Dangerous Reef: approx. 1,650 |
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Seal Bay: approx. 700 |
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The Pages: approx. 2,100 |
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They occur from The Pages (two small islands east of Kangaroo Island), along the southern coast of South Australia and around the Western Australian coast to the Houtmans Abrolhos Islands near Geraldton.
The park supports the third largest colony of Australian Sea-lions with a population of approximately 700 (5% of the world total).
The largest colony occurs at The Pages Conservation Park (approx 2,100 animals), and the second largest on Dangerous Reef, south east of Port Lincoln (approx 1,650 animals). A population census has been carried out monthly at Seal Bay since 1983. The Seal Bay population does not appear to be increasing at present.
There are only a few places on the continent of Australia where Australian Sea-lion's live and breed. Point Labatt is the only place on mainland Australia where Australian Sea-lion pups can be seen growing up and learning to swim and play to hunt and avoid hunters.
See further information on Point Labatt Conservation Park.
Diet
Australian Sea-lions are opportunistic feeders taking a wide variety of prey, particularly squid, octopus, scale fish and some crustaceans.
An adult female Australian Sea-lion, with an unweaned pup, will consume about 8 - 10 kg of food per day whilst at sea. Females are generally away from the colony for 3 days at a time, returning ashore to feed their pups and rest between trips. They range over extensive areas in their search for food and have been recorded 37 km south of Vivonne Bay although they may travel much greater distances than this.
Diving
Sea-lions demonstrate quite remarkable diving abilities. Data from a limited study has recorded a bull diving to a depth of 270 metres (23 times atmospheric pressure) and staying underwater for approximately 7 minutes. Females usually dive to around 80 metres staying under water for 4-5 minutes. An individual will make about 900 to 1,200 dives in a 3 day foraging trip and will only rest for short periods during that time.
Breeding
Australian Sea-lions are the only seal species with a non-annual breeding cycle. The interval between breeding seasons is 17.6 months, and breeding seasons are not synchronised between colonies.
During the breeding season males become aggressive and mate mostly in the 3 breeding areas of the Seal Bay colony, the Eastern Prohibited Area, Western Prohibited Area and Pup Cove. They do not have harems or families as some other seal species do, but defend a distance around themselves in the location of a breeding female. Bulls may stay ashore for up to 4 weeks at a time defending these areas.
Females come ashore in the breeding areas when ready to give birth. Seven to 8 days after the birth of their pup they come into season for about 24 hours and are mated by the resident bull. With female Australian Sea-lions (as with all seals) the implantation of the fertilised egg is delayed for an extended period. Implantation occurs 6-9 months after mating. Pups are usually suckled until shortly before the birth of the next pup.
Mortality Rates
Pups have a mortality rate of about 23% in their first 6 months and between 40 - 50% in the first 2 years. Bulls account for 20% of the mortality rate in pups in the first 6 months, mainly by trampling when challenging another bull. Females come into season when the pup is only about 7 days old, and is still very vulnerable to being harmed by the bulls. Other contributing factors are predation by sharks, poor mothering, disease, breeding areas being inundated by storms/high tides and pups getting jammed in rock crevices. Adult animals are exposed to many dangers in their lives and only about 30% of the pups from each breeding season will reach maturity.
Age
Australian Sea-lions have a life span of between 17 and 25 years. Males mature at 8-9 years, at which stage they start to develop their distinctive white manes.
Females have their first pup at either 4,5 or 6 years of age. This long period between birth and reaching reproductive maturity is one of the factors contributing to the slow population growth of the species.
Moulting
Pups are born with a dark brown to black coat, which is moulted at about 3-4 months of age. They then take on the typical adult female colouration of grey back and creamy chest. They moult again at weaning, then appear to moult at roughly 18 month intervals. The hair takes on a characteristic gingery colour prior to the moulting process.
Weight
Mature males (bulls) weigh 250-350 kg and females approximately 100 kg. Pups weigh about 7 kg at birth and about 30-40 kg at weaning (approximately 18 months).
Parasites
Sea-lions are hosts to a number of different parasites, both internal (tape, fluke and round worms and mites) and external (lice). The presence of lice in the coats of the animals is the reason for the scratching commonly observed.
Further Information
A comprehensive booklet containing information about the Australian Sea-lion and Seal Bay Conservation Park can be purchased at the Seal Bay Visitor Centre. If you have any further enquiries in relation to the Australian Sea-lion contact the Visitor Centre via the following contact details:
Seal Bay Conservation Park
C/- PO Box 39
Kingscote SA 5223
Australia
Phone: (61 8) 8559 4207
Fax: (61 8) 8559 4295
Email: Seal Bay
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