Study Finds Platypus Survival Threatened By Presence Of Dams

A recent study has found that platypus populations are becoming increasingly fragmented as man-made dams are restricting their movement, putting the unique Australian animal’s future under severe threat.

The platypus has recently been listed as “Near Threatened” by the International Union for Conservation of Nature (IUCN), with the species’ population having declined by 30% since the arrival of settlers to Australia over 200 years ago. There are now estimated to be around 30,000 platypuses left in the wild.

Researchers at the University of New South Wales took DNA samples from 274 platypuses from nine rivers across Victoria and New South Wales. Five of these rivers have large dams that reduce the flow of water, whilst the other four are unrestricted (source).

After comparing the samples, the scientists found that genetic differences between platypus populations on dammed rivers was between four and twenty times greater than those of platypuses living similar distances apart on rivers that were not dammed.

This suggests that the presence of dams prevents platypuses from moving freely up and down-river, resulting in isolated populations that are becoming increasingly genetically different from each other.

Platypus vintage print

The scientists found that, due to the dams, the genetic difference between different platypus populations on the same river were as large as those between platypuses living on different rivers.

The study also found that the genetic difference between platypus populations had increased in every generation since the dams had been constructed, suggesting that very few, if any, platypuses had passed around the dams since they were built.

How Are Dams Impacting The Platypus?

Nepean Dam Australia
The Nepean Dam, one of several dams included in the recent study.

Although platypuses are known to cross small dams, larger dams are too big for the animals to pass. Over three-quarters of Australia’s largest dams (i.e., those over 10 meters tall) are found in areas in which platypuses live. The long-term effect this could have on the species is huge.

Attempts to traverse even small dams puts platypuses at risk, as in doing so they are more exposed and are vulnerable to predation from foxes and birds of prey. (source)

Large dams have the effect of isolating platypus populations along a river, resulting in a fragmented population, smaller local population sizes, and limiting gene flow, which can lead to inbreeding.

A dam also reduces the platypuses’ ability to move between areas in response to a change in environmental conditions, such as a flood or drought.

The Benefits Of Dams

Dams are part of one of the most common forms of hydroelectric power generation. River water stored in a reservoir is released in a controlled manner and flows through a turbine, which activates a generator and produces electricity.

Hydroelectricity is the leading source of renewable energy, accounting for around one sixth (almost 17%) of the world’s power.

The use of dams is particularly popular as they form reservoirs that also provide drinking water and irrigation. It is estimated that over the next decade, over half of all new hydroelectric production will come from reservoirs.

Damage Caused By Dams

The construction of a dam not only results in a physical barrier that prevents the movement of animals, but also affects the ecosystem of a river in numerous other ways.

A dam can prevent important nutrients from reaching habitats downstream. The water released from a reservoir is often colder than that of the river, which has been found to affect fish behavior and reproductive capability. (source

Fluctuations in water flow caused by a dam can impact invertebrates such as stoneflies that rely on fast-flowing, highly-oxygenated water. High water flow also helps to keep the riverbed clean, improving the breeding success of many fish species.

Potential Solutions

Scientists have come up with a number of proposals to help the platypus. As well as the prevention of any further dams being built, these include the addition of fish-ladder-style structures to existing dams to enable the platypus to travel up and down-river, and the relocation of platypuses to other areas in order to improve genetic diversity.

Methods that eliminate the need for dams altogether have been developed on other rivers in New South Wales. These involve pumping water from the rivers into off-stream storage areas.

The Platypus: An Australian Icon

Platypus Swimming

With its duck-like bill, rodent-like body and beaver-like paddle, the platypus is famous for its “mix and match” appearance.

After being sent an early platypus specimen, British scientists thought they were being tricked, believing the specimen to be a combination of different animals sewn together. The pelt was even checked for stitches!

The platypus lives in streams and rivers across eastern Australia. This semiaquatic mammal spends much of its time foraging for food in the water, but makes its way onto land to rest in burrows near the riverbank.

An excellent swimmer, the platypus has a highly-distinctive swimming style; although all four of its feet are webbed, only the forelimbs are used for propulsion – the hind feet are used, along with the paddle-like tail, for steering.

Why Is The Platypus Unique?

The platypus is the only member of its family, Ornithorhynchidae, and one of just five mammals that reproduce by laying eggs rather than by giving birth.

Together, these five species (the platypus and four species of echidna) are known as monotremes.

The platypus is also notable for its ability to find prey underwater using electric fields; its extraordinary fur, which glows blue-green in ultraviolet light; and the venomous spurs on the hind legs of the male, which are capable of inflicting a painful wound. (Surprisingly, the venom of the platypus may provide a treatment for diabetes. (source)

The monotremes are believed to have diverged from therian mammals (those that give birth to live young) very early, around 166 million years ago, and the platypus is therefore an important species in the study of evolutionary biology.

The genome of the platypus has been found to contain elements from both mammals and reptiles, as well as two genes only found in amphibians, birds, and fish.

Further Threats To The Platypus

Dams are just one of a range of threats faced by the platypus. Climate change is causing more frequent droughts, which reduce water flow in rivers, while flooding and tropical cyclones have caused several platypus deaths.

Many streams are contaminated with heavy metals and plastic, and entanglement in fishing nets can cause platypuses to drown. This is particularly concerning in small streams where platypus populations may already be very small.

Invasive species are having a negative effect on the platypus, whose natural predators include birds of prey, water rats, and snakes. The introduction of non-native predators such as the red fox and domestic cats and dogs has had a negative effect on the platypus (and many other native Australian species).

As the only surviving member of its family, the platypus is important in the study of evolutionary biology. The species is also an iconic symbol of Australia and is culturally significant to many Aboriginal peoples.

The platypus plays an important role in its ecosystem, controlling populations of invertebrates and providing food for other predators. The loss of this fascinating, unique species needs to be avoided at all costs.