In this section you can read about how many platypus are found in Australia and where they occur:
The platypus’s conservation status is officially listed as “Near Threatened” both in Australia and internationally (as described in the IUCN Red List since 2016). In both cases, the status has been evaluated based on criteria that were defined by the IUCN in 2001 and continue to be used to assess the conservation status of animals across the world.
The platypus’s “Near Threatened” listing has been applied on the grounds that an overall decline in numbers has occurred and – although the decline is poorly defined and inconsistent across the platypus’s range – it may approach though probably not exceed 30% of total population size over three platypus generations (most recently estimated as a period of 21 years) if current threats are not addressed.
Some other animals that are listed as “Near Threatened” in Australia include the Daintree ringtail possum, southern hairy-nosed wombat, Bennett’s and Lumholtz’s tree-kangaroos, heath mouse, dugong, southern elephant seal and southern right whale.
Photo courtesy of P. Hitch
Platypus live only in Australia, inhabiting a diverse array of reliable freshwater habitats from sea level to an elevation of more than 1600 metres near the top of the Australian Alps. Their current range (marked in blue below) extends along the east and southeast coast of mainland Australia from western Victoria to about as far north as Cooktown in Queensland, and also includes Tasmania and King Island. An introduced population is found offshore on Kangaroo Island (marked in pink below), where platypus were released in Flinders Chase National Park between 1928 and 1946 . No subspecies are currently recognised anywhere in the range.
Map adapted from R. Strahan and S. van Dyck. (2008). The Mammals of Australia, 3rd edition. (New Holland: Sydney).
In broad terms, the species is known to inhabit about 80% of the river basins in Victoria, all east-flowing river systems and about 80% of west-flowing systems in New South Wales, and around a third of river basins containing reliably flowing water bodies in Queensland. Predation by salt water crocodiles and severe flooding in the wet season may both contribute to the platypus’s northern distributional limit in Queensland. The species is widely distributed across most of Tasmania, occupying lakes, ponds and glacial tarns as well as rivers and streams. A population is also well established on King Island, which has been isolated from Victoria and Tasmania for at least 10,000 years by the waters of Bass Strait.
Only a few platypus specimens were ever collected in South Australia in the early years following European settlement. Most originated along the Murray River (to as far downstream as Lake Alexandrina), though some were obtained along the Torrens and Onkaparinga Rivers before 1900 (marked by the small green blob and nearby wiggle on the map above). It’s now believed that the species is effectively extinct on the South Australian mainland, apart from animals that may occasionally enter the state after moving downstream along the Murray River from Victoria or New South Wales. The absence of platypus populations in the Northern Territory and Western Australia is thought to reflect the widespread occurrence of crocodiles in the north and the pervasive dryness of the landscape elsewhere.
Severe reduction and even apparent extinction of some platypus populations have been documented to occur in recent decades. For example, platypus have not to the best of our knowledge been seen at any location in the Avoca River basin in western Victoria since 2003. In the Bass River catchment in southern Victoria (where platypus seem to have been widespread until at least the 1980s), the most recent reliable sighting also dates from 2003.
Similarly, a reasonable estimate of platypus population size in the Wimmera River basin in western Victoria at the time of European settlement would be around 1500 animals. By the 1990s this had declined to less than 200 animals, mainly occupying the Wimmera River upstream of Glenorchy township and the Mackenzie River downstream of Lake Wartook. Habitat degradation, channel sedimentation, use of fishing nets and traps in which platypus drowned as bycatch, and regulation of natural flows by the Wimmera Mallee Stock and Domestic System (which by the 1980s exported about half of the upper catchment’s annual flow to storage reservoirs) all contributed to reduced population size. Further catastrophic population losses occurred in the summer of 2006/07, when severe drought caused at least 95% of the Wimmera River upstream of Glenorchy to dry out for months. A few animals survived in the Mackenzie River due to water released from Lake Wartook, but population size was very much limited by the small amount of habitat available (around 12 kilometres of channel). However, the good news is that this population has since grown in size and expanded its range along the Mackenzie River, and platypus are also starting to be seen elsewhere in the Wimmera system.
Population size and density
The carnivorous diet and substantial food requirements of the platypus limit the number of individuals that can exist in a given area. For example, platypus population density in the Shoalhaven River upstream of Braidwood in New South Wales has been estimated to be 12.4-14.5 animals per kilometre of channel. Interestingly, a separate study of platypus prey in the same area concluded that enough food was available to support 13.3 platypus on average per kilometre, helping to confirm that population size is restricted by food availability.
Elsewhere, platypus population density has been estimated to be 1.2-2.1 animals per kilometre of channel in five suburban or outer suburban creeks near Melbourne, and from 2.0-3.6 animals per kilometre of channel in two relatively pristine creeks located in Flinders Chase National Park on Kangaroo Island.
According to the IUCN Red List, between 30,000 and 300,000 platypus are thought to have lived in Australia in 2016. The high degree of uncertainty in overall population size reflects the following:
- Platypus live-trapping studies (currently the only reliable technique for estimating how many platypus occur in a given area) are logistically demanding to carry out, and can only be safely and effectively conducted in a limited range of platypus habitats. Platypus population size has therefore never been studied in nearly all parts of its range.
- Like other wild animals, platypus numbers are expected to fluctuate through time: numbers will drop if mortality rises, breeding declines and/or less habitat or food is available, and rise if these factors improve. Based on what is known about platypus fertility and age at maturity, a population that has lost many members during an extended drought should be able to approximately quadruple in size in as few as 5 years once wetter conditions reliably resume.
Photo courtesy of M. Chalk