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 20 Spring 2001
WOODY DEBRIS IS IMPORTANT
TO PLATYPUS
Woody debris (including branches, sticks
and logs) typically accumulates along a waterway as trees growing on the
banks either shed their limbs or fall over.
In the past, a vast amount of woody
debris was removed from Australian streams and rivers on the grounds that
this material could contribute to erosion or flooding.
More recently, research has shown that
the proportion of bank erosion actually due to snags is quite small. It
has also been found that most pieces of woody debris have little or no effect
on the extent of local flooding-particularly as compared to larger structures,
such as bridge abutments.
At the same time, woody debris appears
to be an extremely valuable resource in terms of contributing to the health
and diversity of streams and rivers.
Along many waterways-particularly those
lined with fine silt or sand-woody debris comprises the most abundant type
of stable substrate in the water, providing a place where small aquatic
animals can cling, perch, lurk, spawn and shelter from strong currents.
While some aquatic invertebrates directly feed on dead wood, many others
are nourished by grazing on the film of bacteria, fungi and algae which
thrives on drowned timber. As well, the turbulence created as water flows
over large logs both oxygenates the water and helps to maintain scour pools
which are an essential habitat feature in their own right.
The importance of dead wood to native
fish has been highlighted by a recent study which found that 94% of young
Murray cod were encountered at sites featuring woody debris. Similarly,
several studies undertaken by the APC have shown that a positive relationship
exists between the amount of woody debris present in the water and platypus
activity or abundance.
For example, in western Victoria's Wimmera
River catchment, three waterways supporting reasonably large populations
of platypus had on average 11 to 19 partly submerged logs or large branches
(20 cm or more in diameter) present in each 50-metre section of channel.
By comparison, in a neighbouring part of the catchment supporting few or
no platypus, an average of only four emergent logs or large branches were
present in each 50-metre stretch of channel.
Along Running Creek and the Little Yarra
River near Melbourne, radio-tracking studies undertaken as part of the Melbourne
Water Urban Platypus Program have revealed that around twice as much woody
debris is present at sites where platypus regularly forage as compared to
unused sections of the streams.
The positive association between platypus
and woody debris presumably reflects the fact that platypus are top predators-mainly
feeding on aquatic invertebrates such as worms and insects. Besides promoting
the development of productive invertebrate communities, the presence of
submerged wood may also improve platypus foraging efficiency by making
it easier for these animals to find their prey underwater.
In short, to help conserve platypus
(and a wide range of other freshwater species) it makes good sense to retain
woody debris whenever possible as an important component of healthy aquatic
habitats.
TAKING A DIVE
What is the best time of year to undertake
visual surveys for platypus?
Research conducted at Toorourrong Reservoir
(a relatively shallow impoundment, 1-2 metres deep, located north of Melbourne
near the APC's research base in Kinglake National Park) suggests that the
answer is at least partly related to the timing of the platypus breeding
season.
Based on surveys undertaken in early
morning, more than twice as many platypus were observed from June through
September (when an average of 3.4 platypus were seen per survey session) as
compared to October (when an average of only 1.6 animals were seen). Over
the rest of the study, from November to January, an average of 2.8 platypus
were spotted per survey session.
Platypus breed in the spring, with eggs
typically recorded in October from Victoria. Given that about a month is
believed to elapse between the time that platypus eggs are fertilised and
the time they are laid in the nest, activity in this species appears to
reach a peak in the period before and during the breeding season.
In the case of females, this is likely
to reflect the fact that they are working hard to store fat which will be
needed while raising young. In the case of males, breeding success presumably
depends on moving around to monitor the reproductive status of prospective
mates-while also doing their best to discourage other adult males from spending
too much time in the vicinity.
By the same token, the relatively low
number of platypus seen in October makes sense if a large proportion of
females are involved at that time in incubating eggs and then caring for
newly hatched juveniles in underground burrows.
Interestingly, platypus also spent more
time on the water surface between consecutive feeding dives in the period
from June through August (32% of activity time) than from September to January
(25% of activity time). In terms of the animals' basic biology, this may
again be related to the timing of breeding: increasing levels of male aggressiveness
in late winter and early spring could well result in the population as a
whole becoming more vigilant-devoting more time to watching other platypus
and scanning their surroundings.
Along with the time of year, weather
conditions have been found to affect the number of platypus observed at Toorourrong.
For example, the number of platypus
recorded in a given survey session showed a significant positive correlation
with the amount of cloud cover: the more overcast the sky, the more platypus
were active during daylight hours.
As well, previous radio-tracking research
has demonstrated that it is extremely difficult to see platypus feeding
on windy days when the water surface is ruffled or choppy. (In consequence,
visual surveys undertaken at Toorourrong are only carried out on calm, wind-free
occasions.)
Based on the results summarised above,
it clearly is important to take both season and weather into consideration
when designing or interpreting observational surveys for platypus-particularly
if there is any intention of comparing the results across waterways or through
time.
To help community groups deal more effectively
with these issues when endeavouring to set up a visual monitoring program
for platypus, an article summarising the full findings of the APC study
is currently being prepared for publication.
Did You Know That....
It is believed
that platypus eggs need to be incubated for a period of about 10 days before
they hatch. A mother platypus keeps her clutch of one to three eggs warm
by grasping them between her curled-up tail and lower belly as she lies in
an underground nest.
USING PLATYPUS TO PLAN
Since beginning its fieldwork programs
in 1994, the Australian Platypus Conservancy has published research results
in a wide range of scientific journals*. The APC is also strongly committed
to sharing new findings about the platypus with management authorities and
members of environmental organisations along with businesses and the wider
community. To this end, the Conservancy continues to generate management
reports, popular articles and special publications about platypus conservation
needs.
In this context, the Australian Platypus
Conservancy has been very pleased to work with Rio Tinto and the Project Platypus Landcare initiative to produce a new publication,
"Using Science to Plan". The booklet was launched in July by Senator Nick
Minchin, Minister for Industry, Science and Resources, at Parliament House
in Canberra.
"Using Science to Plan" is based on
work undertaken by the APC in partnership with Rio Tinto Project Platypus and Earthwatch in the upper catchment of the
Wimmera River since 1997. The booklet describes how platypus research has
contributed to Landcare in this region-both by providing landowners with detailed
information on platypus habitat requirements and by using the animals' status
to help monitor the effectiveness of habitat improvement projects.
Along with demonstrating the value of
wildlife research to practical Landcare work, the publication also highlights
the role of the platypus as a charismatic flagship for stimulating community-based
environmental action.
"Using Science to Plan" is being distributed
to Landcare and other environmental groups throughout Australia, as well
as management agencies, educational institutions, public libraries and interested
individuals.
Copies of the booklet can be obtained
by contacting Rio Tinto Australia, Rio Tinto Project Platypus in Stawell, or the Australian Platypus Conservancy.