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Platypus in Urban Areas
Courtesy of:
The Australian Platypus Conservancy
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The environmental qualities of urban waterways are often
severely compromised. Not surprisingly, platypus and other aquatic species have
struggled to survive as native vegetation has disappeared from stream and river
banks, and drainage patterns altered to suit short-term human requirements.
The platypus was first recorded by European colonists in 1797
near the Hawkesbury River, on the northwestern fringes of modern Sydney. Around
Sydney today, platypus appear to occur in nearby national parks (Ku-ring-gai
Chase to the north and Royal and Heathcote to the south) and upstream of major
water impoundments on the fringes of the greater metropolitan area. Otherwise,
recent platypus sightings are essentially lacking both for the Sydney and
Wollongong regions.
Platypus are believed to survive in a few streams in the
semi-rural western suburbs around Brisbane, and are still occasionally seen
within a short distance of the Hobart city centre. Around Adelaide, the animals
have not been reported from the Torrens River catchment for many decades,
although there is some evidence that the species was probably not very numerous
in South Australia even before European settlement.
There is good reason to believe that platypus were abundant
around Melbourne at the time the city was founded in the middle of the 19th
century. In the 1870s, a "sportsman-cum-naturalist" named Bob Stuart
supported himself by selling platypus skins taken from Merri and Darebin Creeks
and adjoining sections of the Yarra River, in what are today the city's inner
suburbs. While the animals were widely believed to have disappeared from the
Melbourne region by the 1980s because of pollution and habitat destruction,
surveys undertaken by the Australian Platypus Conservancy and Melbourne Water in
the 1990s have shown that platypus still inhabit many urban waterways, albeit
more patchily and at lower densities than would have been the case historically.
Case study - Melbourne Urban Platypus
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The Urban Platypus Program began in 1995 as a joint
initiative of Melbourne Water and Australian Platypus Conservancy. The program
aimed in the first instance to map the distribution of platypus in waterways
around the city and describe their physical condition and population attributes,
including reproductive success. This has been achieved mainly through
live-trapping surveys, although some valuable information has also been obtained
by encouraging the public to report sightings of the animals. Work initially
focused on the Yarra River and its tributary streams, followed by the
Maribyrnong River catchment and other waterways in Melbourne's western suburbs,
the Dandenong Creek catchment in the city's southeast, and waterways flowing
into Western Port.
Surveys undertaken through the summer of 2000 have confirmed
the presence of platypus along nearly half of the waterways where nets have been
set in and around Melbourne.
Interestingly, while lower numbers of animals are found in
urban and suburban habitats than in similar-sized waterways flowing through
forested areas, the physical condition (fat levels) of the two groups is
generally similar. Thus, it appears that platypus regulate their population
density to match the productivity of the local environment - probably through
social interactions which ensure that their numbers do not increase unduly at
any given location.
In the Yarra River catchment, the animals have been
encountered along the Plenty River, Bruces Creek, Diamond Creek, Running Creek,
Watsons Creek, Mullum Mullum Creek, Andersons Creek, Olinda Creek, Steels Creek,
Sassafras Creek, Emerald Creek, Menzies Creek, Stringybark Creek, Woori Yallock
Creek, Wandin Yallock Creek, Cockatoo Creek and the Yarra itself. While it
remains to be established exactly how close to the city centre platypus reside,
a breeding population exists at least as far downstream as the mouth of the
Plenty River, about 15 kilometres from downtown Melbourne.
In the Maribyrnong River catchment, reasonably high numbers
of platypus have been recorded along Deep Creek, Jacksons Creek, and the upper
reaches of the Maribyrnong - again to within around 15 kilometres of the inner
city.
In the Dandenong Creek catchment, by far the largest
remaining platypus population (estimated to include around 30-40 animals)
occupies the length of Monbulk Creek and along Corhanwarrabul Creek (including
the manmande lake in Caribbean Gardens) to as far downstream as the suburb of
Scoresby. A few animals have also been recorded in the upper reaches of
Dandenong Creek itself. Along Ferny Creek in the Upper Ferntree Gully area, a
lone adult male (assessed to be an old animal) captured repeatedly in the
1996/97 field season was not encountered the following year, suggesting that
platypus may now be locally extinct along this waterway.
In the Western Port waterways, platypus have been recorded in
the middle reaches of the Lang Lang River, downstream of Minnieburn Creek.
Longer-term monitoring will establish whether platypus
populations around Melbourne are stable, are declining, or are actually becoming
more numerous as the quality of their habitat is restored through stream
rehabilitation and revegetation projects. For example, one very interesting
finding in the 1997/1998 field season was a record of a juvenile male using a
section of Mullum Mullum Creek where platypus had never been encountered in
three previous years of survey work. The area had been the subject of extensive
channel stabilisation works undertaken by Melbourne Water about one year
earlier, suggesting that the young animal may have colonised the area following
a local improvement in habitat quality. During the 1998/1999 season, more
platypus were found in this particular section on a regular basis and, in
addition, a juvenile female was found at a site a further six kilometres
upstream, providing more support for the idea that platypus are starting to
re-colonise the upper reaches of this waterway in response to habitat
improvements.
Similarly, in 1999/2000 season, platypus were found for the
first time in six years of surveys using the section of Diamond Creek between
North Eltham and Wattle Glen. Again, this aparent recolonisation seemed to be in
response to major habitat improvement works undertaken in recent times.
The Melbourne Urban Platypus Program has been highly
successful in linking the Conservancy's experience in platypus research and
Melbourne Water's expertise in waterway assessment and management - exemplifying
how research and management can be directly and effectively integrated to their
mutual advantage. This co-operation reflects a climate of trust and sense of
genuine shared accomplishment between the two organisations.
Over time, the program has expanded to include studies
providing the first real understanding of platypus habitat requirements in urban
areas. As well, detailed radio-tracking studies have provided information on
specific management issues (such as the effect of bank stabilisation and willow
removal projects on platypus behaviour) to assist the development of "best
practice" protocols for waterway improvement works. In the next few years,
it is also proposed to develop a strategy for re-introducing the platypus to
rehabilitated waterways from which the species has vanished, or potentially
facilitating their introduction to newly created habitats where options for
natural immigration are limited.
The Urban Platypus Program has demonstrated unequivocally
that platypus conservation is an important consideration when managing waterways
across the Melbourne metropolitan region. Reflecting the enduring interest in
platypus by both the news media and the local community, It has also been a
remarkably effective vehicle for building community awareness of the need to use
water resources in a sustainable manner.
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