Distribution and numbers

Historic distribution

The distribution of the platypus in Australia spans from Cooktown in northern Queensland to Tasmania (Figure 1). In Queensland, platypuses are primarily distributed in eastern flowing rivers and waterways, but their distribution is limited elsewhere in the state. In New South Wales, platypuses are more common on the eastern side of the Great Dividing Range but do extend into western-flowing rivers and waterways of the Murray-Darling Basin (Grant & Fanning 2007). Platypuses are reasonably widespread throughout Victoria and Tasmania, occupying 26 of 31 river systems in Victoria (84%) and 15 of 19 river systems in Tasmania (79%), but there is evidence for population declines near metropolitan areas (Grant & Denny 1991). Platypuses are considered vulnerable in South Australia, with sporadic records throughout the Mount Lofty Ranges, Adelaide Hills, and the Yorke Peninsula (Figure 1). There is also an introduced population on Kangaroo Island (Grant & Denny 1991). 

Change in distribution

To assess platypus distribution, we collated 16,797 distributional data points from the Atlas of living Australia state atlas databases (ACT Wildlife Atlas Records; BioNet Atlas of NSW Wildlife; Tasmania Natural Values Atlas; Victorian Biodiversity Atlas; WildNet Queensland Wildlife Data; Biological Databases of South Australia), iNaturalist, museum records (Victorian Museum, Queensland Museum, The Australian Museum and the  Smithsonian National Museum of Natural History), trove, and platypusSPOT. For analysis, each distributional data point was assigned to a sub-catchment (HydroBASIN Level 7 sub-catchment; Lehner et al. (2008)). We assessed presence in a sub-catchment based on records, assuming no sightings were indicative of the absence of platypuses while acknowledging problems associated with false positives and false negatives.

Over the last 250 years (1770-2020), platypuses have been recorded in 288 sub-catchments (885,096 km2) across eastern Australia (Figure 2a). There are 412 sub-catchments (1,103,410 km2) within the current IUCN distribution where platypuses potentially occur (Figure 2b). However, the current IUCN distribution for platypuses fails to incorporate areas where platypuses have recently (since 1990) been recorded. We provide an updated distribution for the platypus (Figure 1) which considers hydrologic features by including sub-catchments (HydroBASIN Level 6 sub-catchment; Lehner et al. (2008)) with recent (>=1990) platypus records and those which fall within the currently used distribution and also include three sub-catchments along the Murray River which connects the proposed distribution (two of which have had sightings between 1970 and 1980).

There are increasing reports of localized declines and extinctions of platypuses, but these are inconsistent across the range and difficult to quantify due to scarcity and uncertainty of empirical historical data, particularly estimates of abundances. Relying on reported observations, we quantify changes in platypus distribution using all records (1770-2020) and those over the last three generations (30 years; 1990-2020). We classify data into four periods: <1990, 1990-1999, 2000-2009, 2010-2020 (Figure 3). Increases in the number of sub-catchments over time are attributable to increased reporting rather than an increase in the distribution of the platypus (Table 1). Despite new areas with more recent platypus sightings, platypus sightings have also declined from several sub-catchments. To assess overall change, we calculated the number of sub-catchments within each period, which didn't contain any platypus records in subsequent periods.

Since 1770, platypuses have been recorded in a total of 288 sub-catchments (885,096 km2; Table 1). By 1990, there were 20 sub-catchments that no longer had platypus records in the subsequent periods, representing a distribution loss of 42,418 km2 (Table 1). Between 1990 and 1999, 17 sub-catchments lost record continuity (49,355 km2) and between 2000 and 2009, there were an additional 62 sub-catchments that didn't record a platypus in the subsequent period (150,564 km2). The total potential distribution loss of platypuses since the 1990-1999 period was 199,919 km2, representing a 22.6% decline in the total area that platypuses have been reported.

As platypuses are restricted to waterbodies, we estimated change in the length of river occupied by platypuses across this distribution. Rivers were defined to start at every pixel where the accumulated upstream catchment area exceeds 10 km2, or where the long-term average natural discharge exceeds 100 litres per second (Grill et al. 2019). We assumed that if a platypus was recorded within a sub-catchment, it could occupy all rivers within that sub-catchment. We calculated the length of rivers for each sub-catchment and compared changes since 1990 (Table 1), which indicate a decline of 22.3% in the length of rivers occupied by platypuses in the 1990-1999 period. Given increased fragmentation of rivers due to in-stream barriers, land-use change, and some evidence of localized declines in platypus numbers, the assumption that they occupy all rivers in a given sub-catchment with a record likely underestimates declines in length of occupied rivers.

Discerning between extinction of a species in an area and inappropriate survey effort for detection can be supported with probabilistic models which consider record continuity (Bino et al. 2020), supporting improved monitoring efforts. A lower number of records in the 2010-2020 period compared to the 2000-2009 period may account for some declines. However, given increased accessibility of reporting and records in 18 additional sub-catchments where platypuses had not been reported, it is possible that platypuses no longer occupy the sub-catchments they were not reported since 2010, but this warrants further investigation. Estimated declines may be greater but cannot be quantified given the significant knowledge gaps (i.e., areas without any platypus observations) across much of the species potential range (Figure 2b). Some sightings in South Australia (Yorke Peninsula and Fleurieu Peninsula) and western Victoria were possibly false identifications, given platypuses are assumed to no longer occupy these areas, warranting systematic confirmation. The inclusion of likely false positive data in this analysis may mask further declines in some sub-catchments.

Historical numbers

Historical accounts of platypuses and numerical data from the fur trade suggest that platypuses were abundant at the end of the 19th century (Table 3). In the Sydney markets, 9315 skins were sold between 1891 and 1899 (Hawke et al. 2019a). Sportsmen reportedly shot hundreds and sometimes thousands of platypuses, given that each garment or rug normally required more than 50 platypus skins. One furrier stated he had sold over 29,000 skins before the first world war  (Hawke et al. 2019a).

Table 3. Quantitative historical records of platypus numbers (> 10) from digitized newspaper articles.

• Year

  1865

  Location

  Shoalhaven River

  Number of platypus

  16-18

  Time/area

  “in a few hours”

  Event

  Shooting

• Year

  1881

  Location

  Severn River

  Number of platypus

  18

  Time/area

  “on an expedition”

  Event

  Shooting

• Year

  1894

  Location

  Murrumbidgee River

  Number of platypus

  10

  Time/area

  “in one day”

  Event

  Spearing

• Year

  1908

  Location

  Yarra River

  Number of platypus

  22

  Time/area

  “in a day”

  Event

  Capture

• Year

  1933

  Location

  Georges River

  Number of platypus

  8-10 & 15

  Time/area

  “at once”

  Event

  Sighting

• Year

  1934

  Location

  Morwell River

  Number of platypus

  13

  Time/area

  “in two pools”

  Event

  Sighting

• Year

  1937

  Location

  Snowy River

  Number of platypus

  15-20

  Time/area

  “at once”

  Event

  Sighting

• Year

  1954

  Location

  Gloucester River

  Number of platypus

  40

  Time/area

  “at once”

  Event

  Sighting

Historical qualitative literature also highlights how populations declined in response to the fur trade. Platypuses were described in records as highly abundant before the 1890s, then records suggest that they began to decline (Table 4).

Table 4. Qualitative historical records of platypuses from digitized newspaper articles.

• Year

  1865

  State

  QLD

  Location

  Pike’s Creek

  Observations

  
  “Platypus found in nearly every water hole”
   

• Year

  1865

  State

  NSW

  Location

  Yass River

  Observations

  
  “The platypus is also found in the banks of the stream in very large numbers”
   

• Year

  1875

  State

  NSW

  Location

  Campbell’s River

  Observations

  
  “Immense numbers of platypus are found”
   

• Year

  1879

  State

  NSW

  Location

  Not reported

  Observations

  
  “Still common in most rivers and creeks of NSW and in some districts found in considerable numbers”
   

• Year

  1890

  State

  NSW

  Location

  Hay

  Observations

  
  “platypus are now nearly extinct”
   

• Year

  1893

  State

  SA

  Location

  Not reported

  Observations

  
  “formerly found in some of the few permanent streams of SA, has disappeared from this country, and in other exists in rapidly diminishing numbers”
   

• Year

  1900

  State

  NSW

  Location

  New England Region

  Observations

  
  “he has not seen in his district a wallaroo or platypus for fifteen years…where they once abounded in thousands”
   

• Year

  1904

  State

  TAS

  Location

  Not reported

  Observations

  
  “numbers are steadily decreasing, and if they continue to do so there is danger of extermination at no very distant date”
   

• Year

  1905

  State

  NSW

  Location

  Not reported

  Observations

  
  “They were numerous, and now they are only a few to be seen”
   

• Year

  1909

  State

  NSW

  Location

  Not reported

  Observations

  
  “but the platypus and the opossum are rapidly becoming extinct”
   

• Year

  1910

  State

  VIC

  Location

  Moorabool River

  Observations

  
  “becoming almost extinct, and is rarely met within the vicinity of large towns”
   

• Year

  1910

  State

  NSW

  Location

  Not reported

  Observations

  
  “these animals are being slaughtered every day and their skin sold”. “these animals are very scare”
   

• Year

  1912

  State

  NSW

  Location

  Not reported

  Observations

  
  “still very scare, and in some districts quite extinct”
   

• Year

  1923

  State

  QLD

  Location

  Not reported

  Observations

  
  “the platypus is all but extinct”
   

• Year

  1924

  State

  NSW

  Location

  Not reported

  Observations

  
  “become almost extinct’’
   

• Year

  1926

  State

  NSW

  Location

  Not reported

  Observations

  
  ‘’once so common in some of our creeks and rivers, is also becoming a rarity’’
   

• Year

  1927

  State

  QLD

  Location

  Not reported

  Observations

  
  “the platypus is nearly extinct”
   

• Year

  1927

  State

  TAS

  Location

  Not reported

  Observations

  
  “The platypus is not a disappearing species but an increasing one”
   

• Year

  1928

  State

  VIC

  Location

  Not reported

  Observations

  
  “they are far more numerous than they were ten years ago”
   

• Year

  1929

  State

  QLD

  Location

  Cooroy

  Observations

  
  “It has been many years since one of these animals has been seen locally”
   

• Year

  1930

  State

  NSW

  Location

  Wyong

  Observations

  
  “For the first time in 20 years a platypus has been caught”
   

• Year

  1932

  State

  QLD

  Location

  Eumundi

  Observations

  
  “This is the first one seen in the locality for a full decade, though at one time they were numerous”
   

• Year

  1936

  State

  NSW

  Location

  Macquarie River

  Observations

  
  “it is years since a platypus has ever been caught in any of the western rivers; it is a long time since a platypus has been seen on the Macquarie, although in days gone by they were to be found there in hundreds”
   

• Year

  1937

  State

  NSW

  Location

  Murrumbidgee River, Wagga

  Observations

  
  “This is the first platypus seen in the district for a great many years’’
   

• Year

  1940

  State

  VIC

  Location

  Murray River, Echuca

  Observations

  
  “This must be one of the very few left in the country”

The fur trade likely had a significant impact on population numbers (Hawke et al. 2019a; Hawke et al. 2019b). Populations may have recovered in some areas after protection in 1912 (e.g., 22 platypuses captured near Princes Bridge in 1908, 16 years after the species received legal protection in Victoria). At the time, there was also widespread land clearing in south eastern Australia (Walker et al. 1993), along with river regulation through the building of dams (Kingsford et al. 2011) and diversion of water. These synergistic human-driven threats in conjunction with low finite growth rate (λ=1.075 and λ=1.0047) (Bino et al. 2015; Fox et al. 2004, respectively), based on current estimates of juvenile recruitment (Grant et al. 2004; Serena et al. 2014) and survival (juvenile females Φ = 0.27 ± 0.04sd, juvenile males Φ = 0.13 ± 0.02sd) (Bino et al. 2015), continue to drive declines.

Contemporary numbers

Knowledge of platypus abundance across the distribution of the species is limited. They are generally considered common, but there is mounting evidence of localised declines and extinctions (Bino et al. 2019; Hawke et al. 2019a; Woinarski et al. 2014). There are few studies able to assess changes in populations trends, most of which have been undertaken at relatively localised scales, highlighting knowledge gaps across the range. We compiled available platypus literature (peer reviewed articles, reports, theses; 220 sources), resulting in 127 studies that undertook surveys or used platypus samples that could be assigned to a river region (Geoscience Australia 1997). Studies mainly focused on populations in Tasmania, the greater Melbourne area, and south eastern NSW (Figure 6).

Some of these studies provided data for estimating catch per unit effort (catch per hour) or density (since 1990). The number of platypuses captured per hour during surveys ranged from 0.004-0.64 (mean = 0.19 ± 0.15sd). Differences among states also reflects capture methods, as fyke nets have more commonly been deployed in Victorian and Tasmanian studies, compared to studies conducted in NSW, which have most often used gill nets to sample larger water bodies.

Some of these studies provided data for estimating catch per unit effort (catch per hour) or density (since 1990). The number of platypuses captured per hour during surveys ranged from 0.004-0.64 (mean = 0.19 ± 0.15sd). Differences among states also reflects capture methods, as fyke nets have more commonly been deployed in Victorian and Tasmanian studies, compared to studies conducted in NSW, which have most often used gill nets to sample larger water bodies.

Figure 6. The distribution and number of studies (peer reviewed articles, reports, and theses) across the distribution of the platypus.

Figure 7. The average catch per hour (± SD) of platypuses across years (1992-2018) for a) different states: NSW (blue), VIC (orange) and Tasmania (grey) and b) different net type: mesh nets (red ), fyke nets (blue), and combined nets (green).