From time to time, work has to be carried out which
affects waterways in various ways. This may range from building large and
relatively permanent structures, such as dams and bridges, to low key activities
such as removing weeds or fumigating rabbit burrows along the edges of a
creek.
All such work has the potential to disturb local platypus
populations to a greater or lesser extent. However, with careful planning,
there is no reason why the harmful effects of construction activities cannot
be greatly reduced or even eliminated.
Checklist for planning major projects
affecting streams and rivers
How can it be determined whether platypus reside
in a waterway?
If no recent sightings of the animals have been made
but it is believed that the area has the potential to support platypus, it
may be worthwhile to organise a preliminary
visual survey or local Platypus Watch project. Preferably, a live-trapping survey
should be commissioned to establish the status
of the local platypus population.
If key areas of platypus habitat within the project
area need to be identified, a radio-tracking study can establish the location
of platypus burrows and identify important foraging areas.
How will the proposed work affect platypus living
in the vicinity?
The home ranges of adult platypus are surprisingly large,
with radio-tagged adults often travelling several kilometres in a single
night. Even juvenile platypus, which normally have smaller home ranges than
those of adults, generally occupy at least a kilometre of waterway. Each
platypus has access to numerous burrows scattered along the length of its
home range.
Accordingly, activities affecting a relatively short
section of waterway (less than 100 metres long) are unlikely to have an appreciable
impact on platypus living in the vicinity - as long as the bank and channel
habitats recover within a reasonably short time after the project is completed
and water quality is not degraded by work-related sediment or other forms
of pollution.
If more extensive activities are planned, a good rule
of thumb is that platypus are likely to be able to cope with the level of
change as long as no more than 20% of the project area is substantially
affected by works in a given year. Projects that only affect vegetation
on the bank (such as poisoning blackberries or removing willows) are less
disruptive to platypus foraging patterns than those in which the banks or
channel are physically remodelled, and can therefore be undertaken over a
larger area - as long as herbicides or other chemicals are not introduced
to the aquatic ecosystem either directly or in storm runoff. In cases where
a target weed species covers the bank more or less continuously for 500 metres
or more, consideration should be given to staging removal programs so the
weed is eradicated on one bank in one year and the opposite bank in the following
year.
A key consideration in any project, large or small,
is to ensure that areas of bare soil or dead plants are covered as quickly
as possible by living vegetation - including indigenous understorey species
as well as trees. This step is essential both to reduce the potential for
soil erosion and help restore the health and productivity of the local aquatic
environment.
How can work be scheduled to minimise the risk
to young platypus in burrows?
Across their range, female platypus mainly lay their
eggs from August through to early November. After incubating up to three
eggs in a nesting burrow for an estimated 10 to 11 days, the mother feeds
her young for several months before they first enter the water in January
through March. Any disturbance to the nesting burrow prior to the juveniles'
emergence may well be fatal to the young animals.
Especially along waterways where platypus are known
to be abundant, consideration should be given to scheduling work for the
autumn or winter if it involves disturbing substantial areas of bank. If
this is not feasible, an effort should at least be made to identify active
nesting burrows so these sites can be avoided as work proceeds.
How can works best contribute to improving platypus
habitat?
* A "soft engineering" approach, in which large rocks
are used to moderate flows or stabilise banks, is always much better than
using concrete to do the job - particularly if more than 50 metres of channel
are affected.
* Works which are designed to allow platypus (and other
freshwater species) to travel freely along the length of a waterway are
always much better than those which potentially hinder such movements.
* Works which maintain or improve habitat diversity
along a waterway by encouraging a range of depths and flow rates are nearly
always preferable to those which create a more uniform channel.
* Sections of vertical bank at the water's edge will
provide habitat for platypus burrows.
* Use of heavy machinery which disturbs or compacts
the banks or disrupts native vegetation should always be kept to a minimum.
* Sediment traps should always be placed in the channel
immediately downstream of work sites (and, if necessary, on the banks) to
intercept loose soil and reduce environmental problems arising from increased
water turbidity and sedimentation rates.
ASSESSING LOCAL PLATYPUS POPULATIONS
The Australian Platypus Conservancy
co-operates with management agencies and local councils to conduct surveys
and radio-tracking studies designed to help conserve platypus populations
in specific waterways.
Such research should ideally be planned
well in advance of major capital works or development activities.
For advice and information on conducting
an environmental impact assessment or developing a conservation management
plan for platypus in your area, contact: