Newsletter of the AUSTRALIAN PLATYPUS CONSERVANCY
ISSUE
36 - October 2007
In 1994, the APC and Melbourne Water started working
collaboratively to develop the Melbourne Platypus Research Program. The program focused initially on mapping
where platypus occur and how many are found across the Yarra River catchment.
By the end of the 2006/07 field season, 223 overnight live-trapping
surveys had been completed in this system.
More than 99% of this netting activity was based on the use of fyke
nets, which—when properly set and checked at regular intervals through the
night—provides a very safe technique for capturing the species.
However, no field technique is perfect from every point of view,
and one disadvantage of using fyke nets is that they do not capture platypus
efficiently in water that is more than about knee-deep. In turn, this has limited their use in the
Yarra catchment mainly to streams, with just a few survey sites located along
the Yarra itself (mainly in the shallower upper reaches around Warburton).
Hence, most of what we know about the platypus population occupying
the Yarra River channel has been extrapolated from sightings of the species
reported to the APC by local human residents.
The sightings database has served to confirm that platypus are
regularly seen along the Yarra River to at least as far downstream as the
middle Melbourne suburbs of View Bank and Lower Templestowe, with courtship
behaviour (animals following or circling each other in an amicable manner)
occasionally observed in these areas.
In turn, this suggests that local habitat quality is good enough to
allow platypus to raise young successfully, at least in favourable years.
Intriguingly, some evidence also suggests that platypus have been
moving farther downstream along the Yarra in recent years, with sightings made
within 10 kilometres of Melbourne’s CBD (as the river flows) by four reliable
observers in the period from 2005-2007. By comparison, no platypus sightings
were reported for this area from 2002-2004.
While one-off reports of platypus sightings can provide interesting
and valuable information, their usefulness as a population monitoring technique
is limited by the unstructured nature of the data.
Accordingly, the Conservancy is launching a new program—Platypus
Count—as an integral part of the Melbourne Water Platypus Research Program.
The program will rely on volunteer participants who agree to watch
for platypus on a systematic basis when they go for a walk or are otherwise
engaged in quiet contemplation of the Yarra in their neighbourhood. Platypus sightings (or lack of sightings)
will be recorded on standardised data sheets and handed in at quarterly
intervals so regular feedback on the study’s findings can be provided.
Given the very high level of interest in platypus evident among
Melbourne’s human population, and the fact that the animals can be seen with
reasonable regularity along many parts of the Yarra, we believe that Platypus
Count will be a rewarding as well as useful way for people to assist
platypus conservation in the metropolitan area.
Persons wishing to become involved in Platypus Count are
strongly encouraged to contact the APC to register their interest.
Did You Know That....
When viewed from above, platypus
are dark brown, apart from a white spot located just in front of each eye. The spots make it appear that a platypus’s
eyes (which normally are tightly shut when diving) remain open underwater. This may fool some predators into thinking
that a submerged platypus will see their approach and flee, reducing the
likelihood of an actual attack.
CAUGHT IN THE TRAP
The APC is pleased to receive several hundred reports of platypus
sightings each year. Sadly, these
records also describe many examples of unnecessary and avoidable platypus
deaths, quite often related to fishing or yabbying.
For example, drowned platypus were recently discovered on two
occasions in folding “opera house” yabby nets in a river near Jenolan Caves in
New South Wales, despite the fact that use of such traps has been banned in
eastern New South Wales rivers since 2003.
These nets can be used to the west of the Newell Highway (where
platypus rarely are found), after modifying the net entrance by adding a wire
circle to discourage entry by other air-breathing species such as cormorants
and turtles.
Likewise, since September 2001 the use of “opera house” nets and
similar enclosed yabby traps have been banned in public waterways in Victoria,
with a $500 on-the-spot fine applicable.
Unfortunately, many people remain unaware of current fishing
regulations, and opera house nets can be purchased in many outdoor recreation
shops with no labels or signs warning of the risk they pose for platypus.
Other types of illegal fishing activities also
continue to cause problems for the animals, as illustrated by a recent report
from a canoeist who found two dead platypus in an abandoned gill net floating
in the Aire River in southern Victoria.
Legal angling practices can also contribute
to platypus mortalities. For example,
we’ve received many reports of a platypus carcass being recovered with a
fishing hook embedded in the animal’s bill or a webbed front foot. Unfortunately, if an angler simply cuts the
line after a platypus has become inadvertently hooked, the animal is likely to
lose condition and die due to difficulties in feeding, or else drown when the
trailing line snags on an underwater object, such as a submerged tree branch or
root.
The number of platypus deaths which occur annually as a by-product
of fishing and yabbying is difficult to estimate exactly.
However, a previous analysis of platypus sightings reports received
by the APC from 1995 to 2002 revealed that 3% of all reports mentioned that the
animal had been hooked on a fishing line or was seen carrying a fishing hook
and line, and an additional 3% described platypus found dead in nets of various
descriptions (including many cases of multiple mortalities). In the same period, around 2% of platypus
captured and handled by APC researchers had loops of discarded fishing line
caught around them, in many cases causing severe lacerations to develop.
What can be done to improve these grim statistics?
1. If you happen to notice a platypus
feeding near you while you’re angling, move a short distance upstream or
downstream to reduce the risk of catching the animal on your hook.
2. If you do accidentally snag a platypus,
make every sensible effort to reel the platypus in and remove the hook from its
mouth or foot—taking care to avoid the poisonous spurs present on the heels of
adult males.
3. Make it your habit to pick up fishing
line left along a stream or river and dispose of it properly—including line
left by others.
4. Report illegal nets ASAP to the relevant wildlife management authority
(in Victoria, contact Fisheries Victoria on 13FISH or 133474).
MORE TRANSLOCATION NEWS
In the last issue of Ripples, we reported that the results
of a live-trapping survey carried out in March confirmed that at least three
juveniles were recruited this year into the recently established Cardinia Creek
population. This brought the total
number of marked animals in the population to sixteen: ten individuals
translocated from other catchments plus six home-grown juveniles.
More recently, a fourth juvenile female (christened “Pamela”) was
encountered in a monitoring survey carried out in September. The unmarked animal was captured farther
upstream than the other three juveniles recorded in 2007, at a site located
about 1.5 kilometres west of Cardinia Reservoir in the suburb of Beaconsfield
Upper. She weighed 840 grams, was
judged to be slightly above average in terms of her physical condition, and was
otherwise lively and healthy.
Along with the new female, juvenile female “Patty” (whose photo
appeared in the last issue) was recaptured at the same site where she was first
recorded in March. Her weight had
increased from 925 to a robust 980 grams in the intervening 23 weeks, while her
body length had grown from 307 to 335 millimetres.
Two adult males were also recorded in the September monitoring
session: “Berwick” and “Beaconsfield” were both released along Cardinia Creek
as juveniles in April 2005, and so were nearly three years old when most
recently recaptured.
Importantly, all
three of the males translocated in 2004 and 2005 are now known to have survived
to at least 2007. Similarly, while just
one of the three females released in 2004 and 2005 actually entered a survey
net in 2007, the survival of all three females has been confidently inferred
based on the number and distribution of juveniles marked this year.
PLATYPUS SIGHT AND SOUND
For unknown reasons, the APC has recently received a large number
of emails asking for information about platypus vision and hearing. In case some of our readers may also be
curious about how the platypus’s senses differ from our own, we thought we
would share what we know about this topic.
The platypus’s eye is small (just 6 millimetres in diameter) and
comes equipped with an eyelid and a round pupil. The eye’s internal structure is typically mammalian in most
respects but does include some reptilian features, such as the presence of
double (as opposed to single) retinal cone cells used to perceive colour. Intriguingly, while a platypus rarely if
ever opens its eyes when submerged, the structure of its lens—curved on the
inner surface and quite flat on the outer surface—is most similar to that of
aquatic mammals such as sea lions and otters that rely on sight to help capture
underwater prey. The most obvious
explanation is that the platypus’s ancestors may have used underwater vision
much more regularly than the modern animal.
In contrast, there
is no evidence that platypus hearing is
in any way specifically adapted for use in the water. Notably, no special
mechanism has ever been identified for water-borne sounds to be conducted to
the inner ear. Like platypus eyes, the
structure of platypus ears resembles that of most other mammals while
incorporating a few primitive features, such as the fact that the ear region is
enclosed in cartilage rather than bone.
While no one is ever likely to know what a symphony sounds like to a platypus, it has been established that
the animals’ hearing is most sensitive to frequencies around 4
kilohertz—exactly the same as in humans.
However, the platypus’s upper hearing threshold (15 kHz) is lower than
the corresponding threshold for people (20 kHz).
FRIENDS
OF THE PLATYPUS
You can support the work of the Australian Platypus Conservancy by joining
Friends of the Platypus.
Benefits include:
A copy of Living
with Platypus booklet.
A subscription
to Ripples.
Special
members’ rates for purchase of posters, cards, booklets and other platypus
materials produced by the APC.
Join now and your initial membership will be valid to 30 June 2009.
Simply fill in the details below and send to the Australian
Platypus Conservancy.
Name_________________________________
Address_______________________________
__________________Tel
No.______________
Email_________________________________
Individual
Membership ($30) ________
Family/School/Non-profit
Group($45)________
Full-time Student
($20) ________
Business/government
dept ($100) ________
Overseas (add
$10) ________
Research Donation*
(optional) ________
TOTAL $_______
*Donations of $2
or more are fully tax deductible.
Payment by:
cheque/money order (payable to Australian Platypus Conservancy)
Visa/Mastercard number:
Cardholder:__________________________
Expiry:_____________
Signed:___________________
Date:_______
SPECIAL THANKS
TO OUR SUPPORTERS!
The Australian Platypus Conservancy is a non-profit research and
conservation organisation. The success
of the APC’s programs relies on the support of businesses, management agencies
and individuals sharing our interest in one of the world’s most amazing
animals.
We gratefully acknowledge special recent help by the following
supporters:
- Commonwealth Department
of Families, Community Services
& Indigenous Affairs
- Alan Lane & Virginia
King
- Melbourne Water
- John T Reid Charitable Trusts
- Wimmera Catchment Management Authority
The APC also thanks the many other groups which continue to assist
its work, including:
Australian Geographic; Commonwealth Department of Environment & Heritage; Corangamite Catchment Management Authority; Danks Trust; Decor Corporation; ESRI Australia; Glenelg Hopkins CMA; Goulburn Broken CMA; Sara Halvedene Foundation; Healesville Toyota; City of Knox; City of Manningham; Microchips Australia); Shire of Nillumbik; North Central CMA; North East CMA; Parks Victoria; Platypus Technology; R.E. Ross Trust; Sonoco Australia; Stradbroke Printing; Helen Macpherson Smith Trust; Victorian State Government; Wilbow Corporation; Wilderness Wear; West Doncaster & Templestowe Veterinary Centres; West Gippsland CMA; City of Whittlesea; Shire of Yarra Ranges
Australian Platypus Conservancy
P.O. Box 22
Wiseleigh VIC 3885
Tel: (03) 5157 5568
E-mail: platypus.apc@westnet.com.au
www.platypus.asn.au