The duck-billed platypus is one of the most evolutionary distinct mammal alive today. It is the only representative of an entire family, Ornithorhynchidae, dating back to the Cretaceous period (146-65.5 millian years before present). The other more recent members of the family became extinct during the Oligocene and Miocene (34-5.3 million years ago).
The platypus belongs to the order Monotremata. Monotremes are the most distinct of all the orders of living mammals. Some authorities place them in a subclass with extinct lineages separate from all other living mammals. Others have even considered monotremes to be reptiles. There are only five species of montreme in the world today: four species of echidna and the duck-billed platypus.
Monotremes differ from all other mammals in that they lay eggs covered by a shell that hatch outside the mother's body. Monotremes are also unique in that they have only a single passage, the cloaca, for both excretion and reproduction. The duck-billed platypus is an integral part of the biodiversity of many Australian freshwater ecosystems. Its conservation is of considerable importance because of its evolutionarily distinctiveness, unique features and the niche it occupies.
The duck-billed platypus is usually active in the early morning and late evening when it leaves its burrow to search for food. It swims along the bottom of freshwater streams and lakes probing at mud and gravel beds with its highly sensitive bill. Research has shown that electro-receptors in the bill detect the muscle activity of prey. A typical diet consists of a variety of freshwater organisms including crayfish, shrimp, the larvae of water insects, snails, tadpoles, worms and small fish. The home ranges of males overlap those of several females. The male will maintain a burrow for both sexes during the breeding season.
The males posses hollow spurs linked to poison glands. It has been suggested that these are used primarily in fights between males during the breeding season. The female lays eggs in a different type of burrow that she constructs herself. In this burrow the eggs are incubated and hatch. The babies are tiny, blind and naked. They remain in the burrow for about four months during which time the mother provides them with milk. Females begin breeding at 2 or 3 years and typically lay 2 eggs at a time. In the wild platypuses have been recorded as living up to 13 years.
The platypus was hunted intensively for its fur until the early 20th century. Until about 1950 it was also subject to accidental drowning in the nets used by inland fisheries. The species has recovered well from these threats, mainly due to an effective government conservation programme.
Other threats are now presenting problems for the platypus. Habitat disruption caused by dams, irrigation projects and pollution are threatening Australian freshwater systems. Accidental bycatch in inland fishing gear continues to result in some mortality. In spite of these threats, the species has so far continued to inhabit and reproduce in considerably degraded environments. The present distribution of the platypus appears to be little altered from pre-European times. There are almost certainly no naturally occurring populations in South Australia where it once occurred, and its distribution has decreased in the lower areas of the Murray and Murrumbidgee River systems in Victoria and New South Wales. It is probable that commercial and illegal fishing operations within the distribution of platypuses in the lower Murray and Murrumbidgee rivers, are suppressing platypus numbers. A study indicated that the legal fishing nets used in the industry are less of a threat to platypuses than the use of illegal nets used by poachers.
Although the platypus is considered to be common throughout its current distribution, its abundance is difficult to measure and therefore its future conservation status is not easily predicted. Several studies have reported fragmentation of platypus distribution within individual river systems. This has been attributed to poor land management practices leading to stream bank erosion, sedimentation of water bodies and the loss of vegetation at areas adjacent to water courses. There is also currently evidence for the adverse effects of river regulation, introduced species, poor water quality and disease on platypus populations, but these have been little studied.
The platypus is protected by legislation in all the States of Australia where it occurs. Effective government conservation efforts have allowed the numbers of this species to increase from previous reductions. Current fishing regulations have provided a good deal of protection for the species. Regulations include the use of nets with larger mesh size since 1950, as well as other modifications in fishing gear.
Platypuses have been introduced to two streams on Kangaroo Island off the coast of South Australia: Rocky River and Breakneck River. These populations appear to be thriving without any adverse consequences for the native wildlife on the island.
Investigations into the biology of the platypus and interactions with human activities have been noted by scientist as being research priorities. Suggested management priorities include the development and implementation of strategies aimed at reducing the effects of human activities on the platypus and its habitat. Research is continuing into the design of platypus friendly fishing methods with a particular focus on New South Wales where the platypus population appears to be suppressed by fishing activity.
Other suggestions include restricting some fishing activities to estuarine areas where platypuses are seldom found, the provision of air spaces and escape holes in eel traps and prohibiting eel trapping in areas where platypuses are known to occur. Stringent law enforcement would largely protect platypus populations in the inland rivers from illegal fishing activity. Investigations are underway to assess whether Scott creek, a stream in the Mount Lofty Ranges, could support an introduced platypus population. The species has been extinct from the area for about 100 years. Further assessment is needed of the appropriateness of Scott Creek for platypus reintroduction. For example, it is necessary to assess the suitability of banks and permanent pools and the risk of predation by foxes.
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Grant, T. R., Lowry, M. B., Pease, B., Walford, T. R., Graham, K. 2004. Reducing the by-catch of platypuses (Ornithorhynchus anatinus) in commercial and recreational fishing gear in New South Wales. Proceedings of the Linnean Society of New South Wales 125 : 259-272.
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