AUSTRALIAN SEA LION

 

Two Female Australian Sea Lion Bask in the Sun

The Australian sea lion (Neophoca cinerea), also known as the Australian sea-lion or Australian sea lion, is a species of sea lion that is the only endemic pinniped in Australia. It is currently monotypic in the genus Neophoca, with the extinct Pleistocene New Zealand sea lion Neophoca palatina the only known congener. With a population estimated at 14,730 animals, the Wildlife Conservation Act of Western Australia (1950) has listed them as "in need of special protection". Their Conservation status is listed as endangered. These pinnipeds are specifically known for their abnormal breeding cycles, which are varied between a 5-month breeding cycle and a 17-18 month a seasonal breeding cycle, compared to other pinnipeds which fit into a 12-month reproductive cycle. Females are either silver or fawn with a cream underbelly and males are dark brown with a yellow mane and are bigger than the females.

Distinctive characteristics

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 colour. 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 coloured underneath. One adult male was measured diving to a depth of 245 m. 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).

Both sexes of the Australian Sea Lion have stocky bodies, a large head and short narrow flippers. Apart from size, the sexes are easily identified by coat colour. The male is dark brown with mane-like yellow areas on the neck and top of the head. The females are silver grey to fawn on the back and creamy coloured underneath. Pups are born with a chocolate brown fur, which is lost after the first moulting phase.

Most breeding colonies exist on offshore islands, with the exception of Point Labatt in South Australia, Baxter Cliffs (west of Twilight Cove) in Western Australia, and the Bunda Cliffs, Great Australian Bight, which straddles the border between the two states. Forty-two (42%) percent of the total known population are found within the three largest colonies east of Port Lincoln; Seal Bay (on Kangaroo Island's south coast), The Pages and Dangerous Reef (in Spencer Gulf).

The species' breeding range has contracted as the population has fallen. Now-extinct breeding colonies previously existed in the Bass Strait, particularly on Clarke Island and adjacent islands in the Furneaux Group. The Abrolhos Island breeding colony is believed to be much smaller today than it was prior to European settlement. Kangaroo Island's north-easterly coasts, in addition to some islands near Perth and Albany, once hosted now-extinct breeding colonies. 

Dental Formula    I 3/2, C 1/1, PC 5/5, and occasionally PC 6/5.

Size

The maximum length of adult males is about 2.5 m and average weight is 300 kg. The maximum length for adult female is about 1.8 m and average weight is 104 kg. Pups are born at an average of about 70cm and 6.5-8 kg.

Life Span    Live up to 25 years.

Gestation Period    512- 576 days.

Can be confused with

New Zealand fur seals live within the range of Australian sea lions, and the range of Australian fur seals is nearly adjacent to that of this species. Wandering sub–Antarctic fur seals periodically show up as vagrants in mainland Australia and Tasmania. Australian sea lions have a large wide head and blunt muzzle that contrasts with the tapering pointed muzzle of all southern fur seals; they also have proportionately shorter ear pinnae, and there are differences in the size and shape of the toes on the hind flippers. In addition to these features, Australian sea lions can be differentiated from these and all other southern fur seals, based on differences in pelage color patterns and paler coloration of all but adult and sub adult males. Australian sea lions lack the dense underfur of fur seals, and their shorter pelage, exclusive of the mane on adult males, looks shorter and less dense than the more luxuriant pelage of dry fur seals, or the shaggy look of fur seals when they are wet.

Distribution

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 sub adult males has been observed on the coast of Western Australia, it appears that Australian sea lions tend to stay around their haul outs and breeding sites. Females may move with their pups to other haul out areas to nurse them.

Australian sea lions are sparsely distributed across their range, from the Houtman Abrolhos Islands (28°S, 114°E) in Western Australia, along the southern Australian coast to The Pages Islands (35°46’S, 138°18’E) in South Australia. Sixty-six (66) breeding colonies have been identified, with 28 in Western Australia and 38 in South Australia. Vagrants have come ashore in Eastern Australia, as far north as the middle of New South Wales. Australian sea lions breed on at least 51 islands and at several mainland sites. Five sites account for approximately 50% of the annual pup production. At sea, Australian sea lions spend nearly all of their time in waters over the continental shelf.

Ecology and behavior

Australian sea lions are unusual among pinnipeds in having a supra-annual pupping interval, with females producing pups every 17–18 months. Pups can be born at all times of the year, with females at a given site being loosely synchronous with each other, and pupping over an approximately 5–month period. Neighboring sites are frequently on entirely different breeding schedules. Males are sequentially polygynous, establishing territories around individual females, herding them in an effort to keep them from departing until the onset of estrous, 7-10 days after they give birth, when they mate. This pattern is repeated until the male is compelled to go to sea and forage, after which he returns and repeats the strategy. Males defend their territories with guttural clicking, growling and barking vocalizations, posturing, and by fighting with rivals. Pups can be trampled when males are fighting, or moving rapidly to confront rivals and control females, and this can be a significant source of pup mortality.

Female With Pup

Pups are continuously attended for the first 9–10 days after birth. Over the next 5 months females make foraging trips that average 48.5 hours in length, followed by pup attendance periods that average 33 hours. Females suckle their pups for 15–18 months, usually weaning them a month before giving birth again. Some females care for their offspring for up to two years, and can be seen with a juvenile and a new pup. Adult female Australian sea lions behave aggressively toward pups that are not their own, as do adult males to all pups, and will pick them up and throw them high in the air. Pups will play at the shoreline and in tide pools while their mothers are away, and following their postnatal molt, will actively swim on their own.

Adult female Australian sea lions are benthic diurnal foragers. They routinely transit to foraging locations by swimming along the bottom. Mean depth of dives for series of lactating females ranged from 41.5–83.1 m and maximum depth of dives ranged from 60–105 m. Mean duration of dives ranged from 2.2–4.1 minutes, and the longest dive recorded lasted 8.3 minutes. Australian sea lions are fast, powerful swimmers and will porpoise when moving rapidly at the surface.

These sea lions are considered to be non-migratory and sedentary, and probably spend most of their lives near their natal colony. The greatest distance travelled by a tagged animal is approximately 250 km. Predators include great white sharks, and presumably killer whales.

Predation

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. Fisherman also occasionally kill them accidentally by entangling them in their nets. Historically the population was greatly reduced due to sealing.

Feeding and prey

Relatively little information exists on the diet of Australian sea lions. They are thought to concentrate their efforts on shallow–water benthic prey, but take a wide variety of fishes, such as rays, small sharks, Australian salmon, and whiting. Other prey includes squid, cuttlefish, small crabs, and occasionally to rarely penguins, flying seabirds, and small sea turtles. Fishermen complain of sea lions robbing lobster traps and fishing nets. Large prey items may be taken to the surface and shaken apart into swallow able portions.

Exploitation

Australian sea lions defecate nutrient-rich faeces which may provide an important nutrient source for coastal ecosystems. Metagenomic analysis of the bacterial consortia found in the faeces of Australian sea lions found very high levels of nutrient cycling and transport genes which may break down the nutrients defecated by sea lions into a bioavailable form for incorporation into marine food webs.

Diving behaviours indicate that the Australian Sea Lions worked extremely hard to exploit the benefits of their surrounding habitats. The Australian sea lion exceeds the limit (calculated aerobic dive limit) on 79% of dives. Australian sea lions spend 58% of time at sea diving and demonstrate high field metabolism, which allows the sea lions to maximise their time spent at or near the benthos, with 61% of each dive and 35% of their time at sea being spent at the deepest 20% of the dives. When diving, these animals are spending 57.9% of their time at sea spent at depths greater than or equal to 6 m, which can be considered as continuous diving. Seasonal variability in foraging energetics and dive behaviour is likely to be sensitive to regional oceanography, the maintenance costs of female sea lions and their offspring, and the distribution and behaviour of their prey.

The Australian sea lion exhibits strong site fidelity, with a foraging range of at most 300 km from their colony. Australian sea lions sometimes travel inland during tumultuous weather, and have been known to travel up to 9.4 km from the ocean.

Threats and status

The total population of Australian sea lions was estimated at 9,300–11,700 in 1993 and was considered to be stable. This species is protected. A substantial sea lion viewing industry has developed, and is regulated at sea lion colonies in parks to minimize disturbance during the breeding season. Extensive disturbance can cause Australian sea lions to abandon colony sites. Traditionally, Australian aborigines and early colonists took sea lions for food and other products. Harvests by sealers in the 17^th and 18^th centuries reduced the population and extirpated them from areas around Bass Strait and Tasmania. Although now protected, the population has not rebounded fully in numbers or reoccupied all of its former range. Conflicts and interactions with fisheries exist and some sea lions are shot as a result, while others are entangled in fishing gear, although the extent of the problem is not fully understood.

Factors hypothesized include

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

IUCN status    Endangered

Male Australian Sea Lion with a Harem @ South Australia