ISSUE 25 - September 2003
LOW FLOWS AND PLATYPUS: LESSONS FROM RUNNING CREEK
Drought clearly will have a devastating effect on platypus populations if waterways dry up completely. But what if flows simply decline to the point where water becomes stagnant? In theory, this too should be a problem for the animals—many of the small gilled organisms (such as mayfly and caddis larvae) which are important foods for the platypus can only survive in reasonably well-oxygenated water. So how well does the platypus cope when faced with inadequate flows in the real world?
New information relating to this issue was gained last summer along Running Creek, a small stream arising on the eucalypt-clad slopes of Kinglake National Park, north of Melbourne. In contrast, the lower reaches of the creek have been extensively cleared and are mainly used to graze beef cattle.
The APC has been monitoring the platypus along Running Creek since 1999, when a small breeding population was first confirmed to occupy the stream’s middle reaches. The population’s size and distribution have been tracked in conjunction with a comprehensive stream rehabilitation program undertaken by Melbourne Water. In co-operation with local landholders, stands of willows have been progressively removed from the creek margins, and the banks and channel stabilised with rocks where this has been needed to control erosion. The banks have been fenced to limit access by livestock, and substantial numbers of indigenous shrubs and trees planted.
To find out how platypus have responded to these activities, both radio-tracking and live-trapping studies were undertaken in 2003 — a period marked by severe drought, with flow along Running Creek dwindling to a trickle for most of the summer and effectively ceasing for two weeks in April.
Interestingly, under drought conditions, radio-tagged platypus spent most of their time feeding in rehabilitated parts of the stream, with 96% of activity records associated with the two areas where habitat restoration works had been carried out in the summers of 2001 and 2002. By comparison, less than 20% of platypus activity records had been associated with the same two sections of the creek in the summer of 2000, when a similar radio-tracking study was undertaken in the months before habitat works were initiated.
Two factors in particular are believed to have contributed to the greatly increased usage of rehabilitated areas by platypus.
Firstly, the disappearance of densely fibrous willow root mats (which in many places had previously choked the channel) is predicted to have improved the efficiency of platypus foraging, by making it easier for invertebrates to be captured.
Secondly, the rehabilitated areas favoured by platypus typically contained at least 2-3 times more dissolved oxygen through summer and autumn as compared to other sites along the creek. In turn, this difference appeared to be due to a number of factors, including better flow capacity in the absence of encroaching willow roots; improved water aeration at the rocky riffles placed along the channel to stop erosion; and reduced demand for dissolved oxygen after willow roots vanished.
Thus, the Running Creek results have helped to confirm that platypus discriminate in favour of habitats characterised by adequate levels of dissolved oxygen—and that conservation activities which improve this aspect of waterway health can provide a measurable positive benefit for the animals.
Did You Know That....
Platypus burrows are typically located in banks that rise at least one metre above the water and are also thickly covered by overhanging plants – thereby protecting the burrow from erosion and helping to ensure that a platypus can come and go without attracting the attention of predators (such as foxes or large owls).
STILL IN A TANGLE
The Australian Platypus Conservancy conducted its first live-trapping survey along Mount Emu Creek near Skipton (in western Victoria) in August 2003, as part of an ongoing program to investigate the platypus’s status and distribution in rural areas.
One of the nine animals captured in the overnight session — a juvenile female — was found to have a red plastic ring caught firmly around her neck. Fortunately, APC researchers were able to remove the offending item, which appeared to be a safety-seal ring from a carton of cream. Otherwise, as this small animal continued to grow, she would almost certainly have suffered a slow and painful death from strangulation or infection.
This incident was a graphic reminder that the problem of litter entanglement is not confined to urban waterways, where APC surveys have revealed many sorry examples over time.
For example, five of the 67 platypus (or 7.5%) encountered in the Melbourne metropolitan area in the summer of 2002/03 had items of litter caught around them.
Three of the animals (all juveniles) carried rubber bands around their necks, which are unlikely to have caused them serious injury. However, the other two cases were more serious: a young male had a thick plastic band (of unknown origin) already cutting deeply into his neck, while an adult female was encumbered with a potentially lethal noose of nylon fishing-line.
The varieties of litter found on platypus this year can be added to a lengthy list of items that have previously been removed by APC staff, including a plastic cable-tie, a rubber canning jar seal, a gasket seal from a motor vehicle engine, other safety-seal rings, an elastic garment cuff, and a metal ring removed from "Lucky", one of four platypus who can be adopted through the APC sponsorship scheme.
Despite such disturbing findings, some evidence suggests that the impact of litter on wildlife around Melbourne may be dropping. While the 7.5% entanglement rate recorded for suburban platypus in 2002/03 was higher than the previous year’s figure of 5%, both values are below the figure of 10.5% reported in the first three years of Melbourne Water’s Urban Platypus Program, from 1995-1998.
Measures such as the installation of litter traps in stormwater drains, better design of rubbish bins, community "Clean Up" days along waterways, and better public awareness of the problems arising from litter are probably all helping to reduce the amount of trash entering streams and rivers.
Clearly, though, more can and should continue to be done to reduce the hazard posed by litter to platypus (and other wildlife such as waterbirds and tortoises). People can make a genuine contribution by minimising the amount of rubbish they generate and helping to pick up litter from the environment. In addition, cutting through all plastic or metal rings or loops before recycling or disposing of them makes real sense—just in case these happen to end up where they don’t belong.
| Australian Platypus Conservancy | Phone: 03 9716 1626 Email platypus@vicnet.net.au |