Ripples is the
quartlerly newsletter of the Australian Platypus Conservancy. It provides
updates on research in progress and other APC news. Members of Friends of the
Platypus automatically receive each edition
of Ripples.
Ripples Newsletter of the AUSTRALIAN PLATYPUS CONSERVANCY
Issue 15 Summer 1999
IS THE PLATYPUS AN ENDANGERED
SPECIES?
The Australian federal government
and state wildlife agencies in Queensland, New South Wales, Victoria and
Tasmania all effectively classify the platypus as "common", implying that
no direct conservation measures are warranted on behalf of the species.
In contrast, at the concluding
session of the National Symposium on Platypus Biology held in November 1996,
the following resolution was endorsed by a forum of Australia's leading
platypus specialists:
"Although the status of
the platypus is relatively secure in some areas, it is clear from the Symposium
that the platypus is declining, and in some situations disappearing, from
some areas of its current range, particularly in agricultural and urban
landscapes.
The differing perceptions of
government officials and scientists regarding the status of the platypus
may partly reflect the fact that, until recently, most platypus live-trapping
work has typically (and very understandably) tended to focus on waterways
where the animals are expected to be at least reasonably abundant.
Over the past five years, the
APC has been working hard to find out how many platypus survive in waterways
that have been markedly altered by human activities. For example, a major
Conservancy research program is studying the animals in the Wimmera River
catchment, a major wool producing region of western Victoria.
Landowners in this area report
that platypus began noticeably disappearing in the 1970's, apparently in
response to progressive deterioration in the quality of freshwater habitats.
The results of setting nets
to survey platypus over about 150 kilometres of waterway have confirmed that
the animals are absent or found at very low density through much of the
catchment. At best, it appears that the entire Wimmera system (which drains
nearly 10% of Victoria's total land area) currently supports no more than
200 platypus.
The Wimmera study has highlighted
the tenuous position of the platypus in one agricultural catchment. Unfortunately,
there is good reason to believe that this pattern of decline has been repeated
in many other rural areas across the range of the species.
Similarly, while the positive
outcome of surveys undertaken over the past five years around Melbourne
is that platypus have been found in about half the city's waterways, the
bad news is that the animals are gone from the other half. Moreover, there
are far fewer animals living along most of Melbourne's streams as compared
to when the city was founded about 160 years ago.
To protect platypus populations
adequately throughout their range it makes sense to initiate appropriate
conservation actions now, rather than waiting until this freshwater icon
becomes locally endangered through neglect.
In this context, the following
statement from the web site of Environment Australia, the leading federal
wildlife conservation agency, is even more germane:
In recent years we have
learned a lot about the Platypus. However, we need to know much more if we
are to make sure that this remarkable creature survives.
NEW WETLAND WELCOMES
THE PLATYPUS
The platypus will potentially
use many different kinds of artificial water bodies: reservoirs, flood retention
basins, ornamental ponds, recreational lakes and farm dams. However, manmade
wetlands are rarely designed from the outset to be platypus-friendly .
A recent project in Melbourne's eastern suburbs has set out to address this
omission.
Olinda Creek, a tributary of
the Yarra River, arises on the forested slopes of the Dandenong Ranges and
flows about 20 kilometres through Melbourne's urban fringe before reaching
the township of Lilydale. Surveys undertaken by the Australian Platypus
Conservancy since 1996 have demonstrated that this waterway supports a sizeable
platypus population, with 28 individuals (including 12 juveniles) marked
to date. Most of these animals have been encountered in the relatively undisturbed
upper reaches of the creek, with numbers declining downstream. Unless action
is taken to improve the quality of freshwater habitats around Lilydale,
there is a real risk that the platypus population in upper Olinda Creek
will become isolated from the main Yarra population and cease to be viable
over the longer term.
In early 1999, Melbourne Water
carried out stream improvement works along a 700-metre section of Olinda
Creek, at a site located about 2 kilometres upstream of Lilydale. The project
aimed to reduce the risk of local flooding by removing willows and creating
a system of flood retention ponds to divert and store surplus storm water.
Given the desirability of creating additional platypus feeding habitat in
this section of creek, the new wetlands system was also designed to encourage
the animals to use the ponds even during times of low flow.
A secure route back and forth
from the creek to the flood retention system was provided in the form of
a special underground concrete pipe. Platypus are known to travel through
pipes as long as the diameter is not too small nor the length too excessive.
Accordingly, a large diameter pipe has been installed, with an open grate
included about midway along its length so that a platypus can breathe even
if the pipe is completely filled by water. As well, outflows from the new
pond system terminate in relatively shallow rocky slopes rather than steep
vertical drop structures, again improving platypus access.
The wetland ponds themselves
have been specially contoured to provide sections of relatively steep but
stable banks where platypus can build burrows. These areas are being densely
planted to reduce potential disturbance by humans and predators such as
foxes and wandering dogs and cats. Vegetation which overhangs the water's
edge is being encouraged to help hide platypus burrow entrances. To provide
additional protected space and extra edge habitat for platypus use, several
small islands have been built in the ponds. In addition, some of the natural
creek channel has been deepened and a series of shallow rock chutes or riffles
constructed. These changes will both help to moderate post-storm flows and
increase the diversity of freshwater habitats along Olinda Creek.
Conservancy researchers monitored
platypus movements and use of burrows during the construction phase, so
contractors could be alerted if an animal was found sleeping in the immediate
vicinity of heavy equipment. By generating new information on the effects
of construction on platypus behaviour, the radio-tracking work has also provided
useful feedback on how best to implement future capital works programs affecting
the stream zone.
In brief, platypus remained
resident in the general vicinity of construction activities, gradually shifting
their feeding patterns to accommodate the progress of the works. Only one
burrow (unoccupied at the time) of the seven used by radio-tagged platypus
in the works area was destroyed in the course of the project. By continuing
to monitor the Olinda Creek platypus population, it will be possible to determine
whether the number of animals living in the vicinity of the flood retention
ponds increases as predicted, and if so, by how much. Meanwhile, this project
has already demonstrated that new wetlands can easily be made both accessible
and appropriate for use by platypus in the wild.
TRACKING DOWN TRYPS
Trypanosomes are tiny protozoan
parasites found in the blood of all classes of vertebrates, including mammals,
birds, reptiles, amphibians and fish.
In Australia, trypanosomes
have been identified in native rodents, bats, bandicoots, wombats and kangaroos.
A type of trypanosome, known to scientists as Trypanosoma binneyi, has also been described from the
platypus.
Little is known about the life
cycle or other biological characteristics of T. binneyi, apart from the fact that it has been recorded
both in Tasmania and on the Australian mainland. While there is no evidence
to suggest that a platypus is normally harmed by being infected with trypanosomes,
it is possible that this situation may change if an animal is undernourished
or becomes stressed, for example due to aggressive behavioural interactions
during the breeding season.
As far as humans are concerned,
the good news is that there is almost no possibility that people can become
infected with platypus trypanosomes. In part, this reflects the fact that
trypanosomes are spread from one individual to another by blood-sucking
leeches, ticks or biting insects. Only one such species is commonly associated
with the platypus, the platypus tick Ixodes ornythorhynchi,which fortunately does not regard human blood as being tasty
(or even slightly edible).
To learn more about platypus
trypanosomes, the Australian Platypus Conservancy has been undertaking a
collaborative study since 1995 with Melbourne veterinarian Dr Ted Donelan
and staff of the Central Veterinary Diagnostic Laboratory.
To determine if a platypus
is infected by trypanosomes, a small sample of blood is collected after
lightly anaesthetising the animal with isoflurane - a very safe compound
which is also commonly used in hospitals to anaesthetise humans. A thin
blood smear is prepared on a glass microscope slide and examined by an experienced
veterinary pathologist for the presence of the parasites. Trypanosomes
are recognised among blood cells as slender, crescent-shaped bodies with
a wavy edge and short, whip-like tail.
Did You Know
That....
Because platypus are
predators near the top of the food chain and require large amounts of food
to survive (up to about 30% of a given animal's body weight each day), it
is believed that their numbers are most often limited by the availability
of food in the form of aquatic invertebrates - shrimps, yabbies, horsehair
worms, and insects such as diving beetles, mayflies and caddis flies.