Habitat and Ecology
Females become sexually mature at 4.5-6 years of age and males at 6 years or more. The mean age of breeding females is 11 years (McIntosh 2007). The oldest breeding female recorded was aged 24 years, while the maximum longevity recorded is 26 years for females and 21.5 years for males (McIntosh 2007). Age-specific survival probabilities are high (0.98) after six years of age and are similar for males and females (McIntosh 2007).
Australian Sea Lions are unusual among pinnipeds in having a supra-annual pupping interval (Gales et al. 1994, Gales and Costa 1997), with females producing pups every 17-18 months (mean breeding interval is 17.5 months, range 16.0-19.9). Females mated about 7-10 following the birth of a pups. Like most other pinnipeds, there is a 4-6 month period of delayed implantation of the blastocyst following conception. This leads to a prolonged (active) placental gestation of up to 14 months, the longest for any pinniped (Gales and Costa 1997). The annual pregnancy rate of mature females is ~71 % (Higgins and Gas 1993). Pups can be born at any time of the year, with females at a given site being loosely synchronous with each other and pupping generally occurring over a 5-7 month period at a given locale (Higgins 1993). Even neighbouring sites can be 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. 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 killed outright in aggressive acts.
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 three 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. Pups will play at the shoreline and in tide pools while their mothers are away, and following their postnatal moult, will actively swim on their own.
Adult female Australian Sea Lions are benthic, diurnal foragers (Costa and Gales 2003). They routinely transit to foraging locations by swimming along the bottom. Mean depth of dives from a series of lactating females tagged with time depth recorders ranged from 41.5-83.1 m; 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 often ?porpoise? out of the water when moving rapidly at the surface.
These sea lions are considered non-migratory and probably spend most of their lives near their natal colony. The greatest distance travelled by a tagged animal is approximately 250 km. Genetic distinctiveness has been reported between nearby colonies, indicating a high degree of site fidelity and female philopatry (Campbell et al. 2008). At sea, Australian Sea Lions spend nearly all of their time in waters over the continental shelf.
Australian Sea Lions are thought to concentrate their efforts on shallow-water benthic prey, but also take a wide variety of fishes, such as rays, small sharks, Australian salmon, and whiting. Other prey includes squid, cuttlefish, small crabs, and occasionally (perhaps 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 into portions that can be swallowed.
Predators include Great White Sharks (Shaughnessy et al. 2007) and presumably Killer Whales (Ling 2002).