#ThreatenedSpecies of the Week: Australian Sea Lion

The Australian Sea Lion is an iconic Australia creature, but sadly it is listed as Vulnerable under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and as Specially Protected Fauna under the Wildlife Conservation Act 1950.

Historically, the main threat to the Sea Lion was over-harvest due to commercial hunting. Although this activity no longer occurs, populations have not recovered to pre-exploitation levels.

Australian Sea Lion. Picture: L Strumpher
Australian Sea Lion. Picture: L Strumpher

Interactions with the commercial gillnet fishing sector, mortality due to interactions with the rock lobster industry and deaths caused by fisheries-related marine debris are currently considered to be the primary threats to the recovery of the Australian sea Lion.

The Australian Sea Lion has a blunt snout, with small tightly rolled external ears. Males have dark blackish to chocolate brown fur with a whitish crown of the head and nape of the neck, whilst females are more silvery-grey above and yellow to cream below.

Males can become very large, 185–225 cm in length and weighing 180–250 kg. Females are smaller, 130–185 cm in length and weighing 65–100 kg. Pups are chocolate brown in colour with a pale fawn crown until they moult at about two months of age. After moulting, a juvenile’s coat is similar to that of an adult female.

The Australian Sea Lion is the only endemic pinniped (true seals, fur seals and sea lions) in Australian waters.

The current breeding distribution of the Australian sea lion extends from the Houtman Abrolhos Islands on the west coast of Western Australia to the Pages Islands in South Australia.

Estimating the abundance of the Australian Sea Lion is difficult. Techniques used are based on estimates of pup production and the use of population models. Using these techniques, the best estimate for the 2011 population was approximately 14 700 Australian sea lions, with most (86 per cent) occurring in South Australian waters.

Australian Sea Lions use a wide variety of habitats for breeding sites and, during the non-breeding season, for haul-out sites (rest stops, which are also useful for predator avoidance, thermal regulation and social activity).

Onshore habitats used include exposed islands and reefs, rocky terrain, sandy beaches and vegetated fore dunes and swales. They also use caves and deep cliff overhangs as haul-out sites or breeding habitat

The Australian Sea Lion is considered to be a specialised benthic forager — that is, it feeds primarily on the sea floor. Studies have shown that the species will eat a range of prey, including fish, cephalopods (squid, cuttlefish and octopus), sharks, rays, rock lobsters and penguins.

The Australian Sea Lion feeds on the continental shelf, most commonly in depths of 20–100 m. Australian sea lions typically travel up to about 60 km from their colony on each foraging trip, with a maximum distance of around 190 km when over shelf waters.

Australian Sea Lions commonly reach 8–9 years of age, with a maximum age of 12+ years. Females show a high level of natal site fidelity, only breeding at the site where they were born. The species has an asynchronous 17.5 month breeding cycle across its known range.

The pupping season can extend for between five and seven months. Associated with the longer pupping interval present in this species is a longer period of embryonic diapause of four to five months, and a prolonged post-implantation period of up to 14 months. Adult females haul-out a day or two before giving birth and leave 10 days later to forage at sea.

They have their first pups on an average of 4.5 years of age. A strong bond is established between a female and her pup, sometimes lasting from a year to 40 months.

Information Source: Government of Australia, Department of Environment and Department of Parks and Wildlife Western Australia

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