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 22 Winter 2002
AND THEN THERE WERE NONE
The process by which a species or population goes extinct
is most often blamed on chronic threats (such as progressive habitat loss
or over-hunting). However, as populations shrink they also become less able
to survive unlucky chance events, such as droughts or bushfires. Biologists
have coined the term "minimum viable population" to describe the smallest
number of animals that are expected to persist on their own, despite year-to-year
variation in survival.
In practice, computer models suggest that an isolated
platypus population will need to comprise at least 50-60 adults to ensure
that the population has a reasonably high probability of surviving for 100
years or more. Smaller populations are progressively more likely to go
extinct-or, put differently, less likely to survive adverse environmental
pressures when combined with bad luck.
The results of recent platypus surveys along the Curdies
River-undertaken on behalf of the Corangamite Catchment Management Authority-perhaps
reflect a case in point.
The Curdies River is located in southwestern Victoria,
about midway between the regional centres of Colac and Warrnambool. The
catchment generally receives ample rainfall and supports many productive
dairy farms. The down side is that pastures have often been established
right to the edge of the river, with little or no cover provided by native
vegetation on the banks. Comments by local residents also suggest that the
amount of summer flow in the river and its tributary streams has declined
in recent years, so that sections of streams which were once reliably perennial-providing
year-round habitat for aquatic animals-now regularly cease flowing in dry
seasons.
Importantly, the Curdies is also quite a small river,
measuring just 2-6 metres wide in most places. Accordingly, it is likely
that the entire Curdies catchment supported at most a few hundred platypus
at the time of European settlement.
The APC set platypus survey nets in the Curdies system
on two occasions in March 2002, providing replicated sampling of 31 kilometres
of the river between Cobden and Timboon. Platypus were not encountered
on either night.
The absence of animals at survey sites was mirrored
by the pattern of platypus sightings reports-received through articles placed
in the local newspapers and direct discussions with landowners along the
river. In brief, only seven reports of sightings were obtained. Several
persons born in the area stated that they had never seen a platypus nor heard
of anyone else ever seeing one. The only reports of frequent sightings in
any part of the catchment date back to the 1950's, with just two reports
of platypus seen in the 1990's.
Based on the above, while it is possible that a few
platypus survive in the Curdies system, it seems highly unlikely that enough
individuals remain to comprise a viable population.
The restoration of platypus as an integral part of the
Curdies ecosystem may well require that problems relating to river productivity
and health be addressed across the catchment. Happily, the Corangamite
CMA is currently developing a plan to achieve those ends in partnership
with the local community. In this context, the reinstatement of platypus
may best be viewed as both a worthy long-term goal and a biologically appropriate
benchmark for catchment-wide improvement.
KNOWING ABOUT NETS
Platypus are air-breathing animals which can stay submerged
for just a few minutes before drowning - especially when actively swimming.
Accordingly, nearly any type of one-way net set to capture fish or other
edible freshwater fauna (e.g. drum nets, "opera house" or other folding
frame nets, or yabby pots) can potentially kill platypus if the animals
live in the area.
A horrifying example of the slaughter that can be caused
by misusing these nets was reported to the APC last summer by a landholder
living in coastal Victoria. While walking with her children along a forest
stream, she spied a derelict eel net set in the channel. After being retrieved
from the water, the net was found to be full of bones-including a minimum
of 17 confirmed platypus skulls!
While nothing can be known for certain about the circumstances
surrounding the net's history, it was not found in an area where nets of
this type are allowed to be set legally. Furthermore, given that the stream
holding the net was quite small, it is likely that the net had been abandoned
for some time - perhaps the best part of a year or even longer - for so many
animals to become trapped and die.
Because each platypus typically feeds along many kilometres
of waterway, it is also likely that the net decimated platypus numbers over
a very large area upstream and downstream. When flows increased in winter,
platypus entering the net would have drowned. In summer, when the netting
was partly exposed above the surface, they would have starved.
Even when nets are checked on a regular basis, fishermen
report that two or more platypus may sometimes drown overnight in a single
yabby pot. In turn, it is possible that platypus - whose natural diet includes
yabbies - may go out of their way to enter traps holding a source of food.
To limit the potential for platypus (and other air-breathing
animals, such as freshwater tortoises) to be killed accidentally by commercial
fishermen, all of the states where platypus regularly occur place restrictions
on such commercial operators. For instance, eel fishermen operating under
licence in Victoria can only set their nets in a limited number of locations
- chosen in part because they represent habitats where platypus are unlikely
to be found, such as river estuaries.
To protect their own interests as well as non-target
wildlife, it is important that recreational anglers also make sure that they
understand and comply with state regulations designed to conserve natural
populations. In Victoria, for example, yabby pots or other permitted folding
frame mesh traps are only supposed to be set in dams or ponds on private land
- as of September 2001 it is illegal to set such nets in streams and rivers.
More generally, it is vital that people be aware that
fish and yabby nets alike may kill a range of other wildlife. From the
viewpoint of air-breathing animals in particular, the only way to ensure
that the traps are completely safe is to provide an air space at the top
of the non-return chamber when setting a net in the water.
Did You Know That....
The platypus has scent glands
located just beneath the skin of the upper shoulders. The glands of adult
males are most active during the breeding season, when they secrete a pale
yellow, slightly sticky fluid onto the skin-providing males with a strong
and distinctively musky aroma at this time of year. By comparison, female
scent glands are both smaller and less active year-round.
THE INTERNATIONAL PLATYPUS
The amazing platypus has long fascinated people around
the world. The extraordinary hold which the species can have on the imagination
is well illustrated by the case of Winston Churchill. At the height of
World War II, the British Prime Minister asked that a consignment of live
platypus be sent to London. Sadly, the male selected to make the journey
to England died just four days from his destination when anti-submarine
depth charges were detonated under the ship. The platypus was subsequently
stuffed and mounted to become a prized display on Churchill's desk.
The world-wide interest in the platypus continues to
this day. The Conservancy's website (www.totalretail.com/platypus) is flooded
by international visitors seeking information on platypus biology and conservation.
The species is a favourite topic of study in many overseas schools and
colleges, with student projects sometimes leading to a class fund-raising
drive to sponsor a platypus through the APC's program.
In fact over 60% of supporters of the platypus sponsorship
scheme are from overseas. Most of these live in the United States, but
people from Canada, the United Kingdom, Germany, France, Sweden and the
Netherlands have also become involved. A similar story pertains to membership
in Friends of the Platypus. Nearly 25% of those who support the work of
the Conservancy by becoming Friends are from outside Australia. Americans
are again best represented among overseas members, though many others have
joined from a wide range of countries.
Relatively few overseas visitors participate in Conservancy
fieldwork, particularly as the APC tries to accommodate numerous volunteers
from Australian universities and local conservation groups. Nevertheless,
enthusiastic participants have recently included persons hailing from the
UK, USA, Netherlands, Denmark, Austria, Norway and Japan.
The APC's Platypus Insights program is also of great interest to overseas visitors. With
no platypus found in foreign zoos, a trip to Australia provides the only way
to see this remarkable mammal. Accordingly, an Insights tour, offering an exceptional opportunity
to observe a platypus in the wild, is a popular experience for many tourists.
Clearly, although the platypus is a uniquely Australian
animal, it also qualifies as a genuine "World Heritage Species".