Newsletter of the AUSTRALIAN
PLATYPUS CONSERVANCY
ISSUE 39 - February 2009
UPDATE: PLATYPUS, FLOODS AND FIRES
As foreshadowed in Ripples 37, the APC
conducted a study in mid-2008 to examine the effect of major bushfires and
flooding on platypus populations in eastern Victoria. Working in partnership with the Department of
Sustainability and Environment and Parks Victoria, live-trapping surveys were
carried out in the region between Thomson Dam and Bairnsdale, in the upper
catchments of the Thomson, Macalister, Avon and Mitchell River basins.
Platypus were encountered in all four survey areas,
with population densities ranging from an estimated 1.2 adults and subadults
per kilometre of channel (in the Wentworth and Barkly River sub-catchments) to
as few as 0.6 adults and subadults per kilometre (in the Aberfeldy River
sub-catchment).
No direct relationship was apparent between platypus
numbers and the amount of recent fire damage sustained by trees growing in the
vicinity. In turn, this fits with the
fact that platypus shelter in burrows, which should normally protect animals
from the immediate effects of flames, smoke and radiant heat.
In contrast, flood damage (as gauged by the amount of
recent bank erosion and freshly deposited sediment in the channel) was found to
be inversely related to platypus population density: the greater the impacts of
flooding, the fewer adults and subadults were recorded.
Similarly, the
only place where juveniles were not captured (the Aberfeldy sub-catchment) also
appeared to have suffered the greatest flood-related damage, suggesting that
floods can have a detrimental effect on both adult survival and subsequent
recruitment of young animals.
Flooding may cause platypus to die when they drown or are battered by debris carried in
flood waters. They may contract
aspiration pneumonia after inhaling water, lose condition when populations of
their main prey (bottom-dwelling aquatic invertebrates) are swept away, or be
swept downstream themselves and have to find their way home via unfamiliar and
potentially dangerous territory.
Floods may also degrade the quality of the platypus’s
environment over the longer term, particularly if pools become badly clogged by
sand and finer sediment, or erosion flattens out stream banks—increasing the
risk of predation as platypus travel between the water and their burrows.
It would not be surprising if problems arising for
platypus from flooding tend to increase in the downstream direction, along with
the growing volume of water pouring through the channel. Based on anecdotal information, the effect on
platypus populations can be dramatic.
For example, the manager of a caravan park in the
middle reaches of the Macalister River reported seeing platypus regularly in
the four years prior to the devastating flood of mid-2007, with up to seven
individuals observed on any given evening.
Platypus sightings ceased abruptly at the time of the flood, with no
animals seen thereafter up until at least June 2008 (when he was interviewed).
In theory, as long as some platypus survive in a river
catchment, their descendants should eventually repopulate the system—if
recolonisation isn’t disrupted by further major disturbance.
In practice, it will be interesting to see how long it takes for platypus to again be seen routinely at sites where they vanished in mid-2007.
SETBACK TO REINTRODUCTION PROJECT
The program to reintroduce platypus to Cardinia Creek
in Melbourne’s outer southeastern suburbs has generally been a great success
since it was initiated by the APC and Melbourne Water in 2004.
Ten young animals were translocated to Cardinia Creek
from nearby river catchments from 2004 to 2007, with the first home-grown
juveniles recorded in April 2006. Three
or more offspring have been weaned in
each subsequent breeding season, suggesting that the population should be well
on its way to becoming self-sustaining.
Sadly, at least two members of the population are now
known to have been killed in folding “opera house” yabbie traps set illegally
along Cardinia Creek (not far from Beaconsfield township) late last year.
Two different persons reported finding a dead platypus
in an underwater trap over a period of about a week to the Department of
Sustainability and Environment’s customer call centre. A third person reported that he had heard that
the traps were being set by teenagers mainly interested in capturing the large
spiny crayfish which continue to inhabit Cardinia Creek.
Along with crayfish, opera house traps are designed to
capture yabbies, which are eaten by platypus.
Accordingly, a platypus may either swim inadvertently into an opera
house trap or actually be lured into the trap because it holds one or more
edible crustaceans. Having entered the
trap, a platypus will quickly drown—in less than three minutes—unless the top
of the trap projects above the water surface.
In places where platypus are abundant, the toll taken
by even occasional use of opera house traps can be horrific. For example, no fewer than three dead
platypus (one very large and two smaller animals) were recovered from a single
opera house trap set overnight at a popular picnic spot along the Tarago River
(not far to the east of Cardinia Creek) in 2006.
Reflecting the fact that opera house traps and other types of folding frame nets pose a very real threat to a wide range of air-breathing aquatic vertebrates (including native water rats, tortoises and water birds as well as platypus), their use in Victorian public inland waters has been banned since 2001.
Persons holding a valid Victorian recreational fishing
license are permitted to catch yabbies and crayfish in rivers and streams
either by hand or with the help of simple baited lines (without hooks) or
collapsible hoop nets (set flat on the bottom of the channel). It is also legal to use opera house traps in
privately owned off-stream dams, as long as the owner gives permission.
The standard penalty for unlawfully setting an opera
house net is currently a fine of $567.Persons who kill a platypus (which is
gazetted as notable wildlife in Victoria) can be fined up to $12,000 and/or
spend a year in prison.
In response to the totally pointless deaths of
platypus along Cardinia Creek, Fisheries officers are stepping up the frequency
of routine patrols in the area. This
increased vigilance also reflects concerns that the local population of spiny
crayfish—slow-growing creatures which take years if not decades to reach
maturity—is being harvested in an unsustainable manner.
However, given practical constraints on the officers’
time, it’s clear that the community has an important role to play in curbing
illegal fishing practices in this and other areas.
Accordingly,
anyone finding an opera house trap set along Cardinia Creek (or other public
waters in Victoria) is encouraged to ring the Fisheries hotline immediately to
report the matter (13 3474 or 13 FISH).
Did You Know That....
The platypus genome has been recently estimated to include a grand total of 18,527 protein-coding genes (about 15% less than the corresponding number in humans), packaged in a set of 52 chromosomes.
PLANNING FOR
PLATYPUS
As noted in Ripples 29, protecting the platypus
and its environment should be a standard feature of good government
throughout the species’ range. Now, one local council in Victoria has taken the
lead in commissioning a comprehensive Platypus Conservation Strategy.
The Shire of Yarra Ranges is located on the eastern
outskirts of Melbourne. It encompasses a
large area of suburbs and rural fringe, as well as a substantial expanse of
relatively pristine forest in the headwaters of the Yarra River catchment. The Shire has responsibility for more
waterways supporting platypus than any other municipality in the Melbourne
region. Creeks within its boundaries
also contain some of the most threatened
platypus populations in the urban area.
For example, Olinda Creek and Monbulk Creek both support isolated
populations comprising fewer than 30 animals.
The Australian Platypus Conservancy and Shire of Yarra
Ranges are now working together to identify measures to assist the species
locally. This includes establishing a
detailed map of where platypus occur and their status throughout the
municipality. This information can then
be taken into account in the council’s planning procedures, ensuring better
protection of biodiversity values.
The Platypus Conservation Strategy will also include information needed to help set priorities for habitat restoration work by council and community groups, and highlight opportunities for raising awareness of the community’s other roles in conserving the species. In addition, it will review current maintenance practices in council parks and reserves. This may potentially cut operating costs for the Shire—for instance, by reducing the amount of routine mowing required in riparian areas where leaving a buffer of native vegetation is identified as a better option.
The scope of the APC’s visual monitoring programs
continues to grow.
Platypus Count—which relies on volunteers to record platypus
sightings systematically over time at fixed sampling points—now includes
persons living in and near the Australian Capital Territory. Working in partnership with ACT Waterwatch,
the Conservancy presented an information session late last year in Queanbeyan,
not far from the Queanbeyan and Molonglo Rivers. Volunteers are also being asked to keep track
of water rats, which are abundant in many places around the ACT, including Lake
Burley Griffin.
Platypus Count will also expand over the next year to include new
locations in country areas, thanks to a grant from The Norman Wettenhall
Foundation.
At the same time, field trials to develop effective
visual monitoring techniques for use by groups
(funded by the Sara Halvedene Foundation) have yielded very promising
results. As well as TAFE students (see Ripples
38), a number of Landcare groups in East Gippsland have now participated in
early morning or late evening counts of the platypus and water rats living in
their local areas. This has enabled the
recommended protocol for such surveys to be fine-tuned, with the APC now in the
process of developing a self-contained kit for persons interested in setting up
their own monitoring programs in future.
Individuals who would like to become Platypus Count
volunteers in the ACT, Melbourne or elsewhere are encouraged to contact the APC
for more details. Similarly, any
Landcare or other environmental group interested in monitoring platypus and/or
water rats is invited to register with the APC to receive a Platypus Group
Count information kit later this year.
The Conservancy is
very grateful to the following organisations for their support in developing
community-based platypus monitoring programs:
Sara Halvedene Foundation
ACT Waterwatch
The Norman Wettenhall Foundation