|
Although both seals and sea lions are pinnipeds, they differ from each other in a number of ways.
Sea lions have distinct ears and have larger, stronger flippers that they use to walk with. Seals undulate on their bodies to move on land
but are actually better adapted to living in the sea than sea lions.
Seals are more solitary and quieter than sea lions, which are rather noisy gregarious creatures.
The ancestors of sea lions were land dwelling animals and they are most closely related to creatures such as,
bears, raccoons and weasels. It is thought they diverged about 50 million years ago.
The Australian sea lion is endemic to Australia, meaning it is only found here and has not migrated to other lands. The other main
pinniped (pinniped means fin footed) around Australian shores is the New Zealand fur seal.
The population of sea lions in Australian waters is estimated at a little under 15,000 animals. They tend to inhabit offshore islands that are undisturbed by
humans. In Western Australia they range as far north as the Abrolhos Islands and extend east along the south coast into South Australia.
Their breeding cycle is not regular like other pinnipeds and can vary from 17 to 18 months. The length of breeding season can also vary from 5 to 9 months.
During breeding season, males establish a territory on a beach and aggressively defend it. They have been known to kill sea lion pups although
it is presumed these are not ones they have fathered.
Males accumulate a harem of females and will mate with 4 or 5. The females become fertile about 6 days after giving birth but there is disagreement
over the length of pregnancy with some researchers suggesting there is an initial delay before the actual gestation takes place. Typically the young
seem to arrive 512 to 576 days after mating takes place.
Females establish a 'natal site' about 2 days before giving birth. Once the pup is born they remain at the site for approximately 10 days before returning to the
sea to feed. She then returns after a couple of days at sea to nurse for around 30 hours before repeating the feeding cycle.
On average, females only give birth to one pup a season and communicate with their young by sound and scent.
Females may be aggressive to pups other than their own but there are also reports of cooperative rearing where a female will take care of groups of pups
and even adopt pups that have been orphaned. Australian sea lions are the only pinnipeds known to exhibit this fostering behavior.
The pups are weaned off milk between 15 and 18 months of age and due to the erratic nature of breeding, they do not all arrive on mass. They
become sexually mature between 3 and 6 years of age.
Males take no part in rearing of young and when not breeding move to other areas away from the females. A colony of male sea lions exists
on the islands off Shoalwater (Rockingham) and they swim north to islands off Jurien Bay
to mate.
Sea lions eat a range of food but the main diet consists of fish, squid and octopus. They are known to feed on birds (especially penguins) if the opportunity arises.
Typical weight for sea lions ranges from 105 to 300 kg with males being heavier than females. They are usually 1.8 and 2.5 metres in length when fully grown.
The main threats to sea lions come from great white sharks and humans. Although they have been removed from the rare species list, Australian sea lions are fully
protected in Australian waters. While large scale hunting of sea lions stopped in the 1920s, it was not until 1972 that they became fully protected. The current
population is thought to be stable or in slight decline.
|
