A platypus swims underwater with a worm in its mouth

Platypuses come from a group of egg-laying mammals known as monotremes. Image © John Carnemolla/Shutterstock

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Dams threaten populations of Australia's duck-billed platypus

Populations of one of the planet's most iconic mammals are becoming increasingly isolated from each other.

Dam building in Australia is reducing gene flow between platypus groups, piling pressure on populations whose numbers are already falling.

Platypuses are caught in a dam dilemma between protecting the environment and providing renewable energy.

Australian dams, built to provide irrigation and hydroelectric power in the twentieth century, are cutting platypus populations off from one another. Over several generations, these groups are becoming more genetically distinct from one another, with the lack of mixing putting them at risk of inbreeding.

With platypus populations known to be in decline as a result of wider issues of water regulation and habitat loss, scientists are concerned about the added pressure dams are having.

Professor Richard Kingsford, who co-authored a new paper investigating this topic, says, 'This is a profound result with significant implications for platypus conservation.'

'We've long suspected that dams change the availability of platypus prey, but this is the smoking gun. Platypuses just can't get around big dams.'

The study, published in Communications Biology, has called for interventions such as platypus 'ladders' to prevent the instantly recognisable animals from enduring this fate. 

The ruins of Jawa in Jordan

The first evidence of human-constructed dams goes back to the Mesopotamian city of Jawa in 3500 BCE, located in modern day Jordan. Image © Joe Roe, licensed under CC-BY SA 4.0 via Wikimedia Commons

Dammed if you do, dammed if you don't

Hydroelectric power is the leading source of renewable energy today, producing more electricity than all other renewables combined. Overall, it provides around 17% of the world's energy, particularly in the Global South where some countries are almost entirely powered by hydroelectricity.

The use of dams is one of the most common forms of hydroelectric power generation, as they can be implemented alongside other uses of reservoirs such as drinking water and irrigation. Over the next decade, the International Energy Agency estimates that over half of new hydroelectric capacity will come from new reservoirs.

But the flooding of land to create these reservoirs is controversial. Aside from the forced relocation of local residents and habitat destruction, the flooding can release large amounts of greenhouse gases such as carbon dioxide and methane as microbes break down dead plants and soil. 

Some experimental studies also suggest that the flooding of land can also cause an increase in a form of the toxic metal mercury that is more easily taken in by living organisms. 

The dams also cause change to river ecosystems, trapping around a quarter of the nutrients and sediment carried in the water and preventing it from reaching habitats further downstream. When the dams release water, it is also often colder than the river itself which can affect the behaviour and reproduction of fish.

These fluctuations in waterflow can also harm invertebrates such as stoneflies which are dependent on high oxygen levels brought by the river. High flow also helps keep gravel in the river clean, increasing the successful breeding of salmon and other fish.

The researchers behind the current study focused specifically on how dams are affecting platypuses, finding they represent a barrier on the mammal's road to recovery. 

The arched wall of the Nepean Dam holds back the reservoir behind

The Nepean dam was one of a number included in the platypus study. Image © Greg Brave/Shutterstock

How are platypuses affected by dams?

The researchers found that the platypus is particularly vulnerable to the impact of dams, with 77% of all large Australian dams found in areas where the animals live. 

This study focused on nine rivers in particular, comparing the genetics of platypus populations found above and below large dams with each other and from populations on undammed rivers. 

The dams act as a barrier between platypus populations, with the genetic differences between platypuses living on either side of a dam increasing with each generation after the dam's construction. 

While there is currently no evidence of inbreeding, it becomes more likely the longer the populations are separated. 

Lead author Dr Luis Mijangos says, 'Inbreeding within platypus populations is likely to have a significant impact in the coming generations, particularly for very small populations below 100 individuals.'

While it is possible that platypus may be able to climb around some of the dams in the study, it would put them at an increased risk of predation from animals such as invasive red foxes. 

The study's authors instead advocate for the investigation and implementation of methods to link populations separated by dams, including the relocation of individuals between groups and structures similar to fish ladders that would allow the mammals to climb to the top of the dams.

In the future, the researchers hope to investigate how dams are affecting the overall health of platypuses, and if they are producing changes in associated genes.

Dr Gilad Bino, another co-author of the study, says, 'We know that platypuses are declining in many parts of their range in eastern Australia and are affected by many threats.'

'There is still much we don't know about the ecology of the platypus, but given its international status as a monotreme, it is increasingly vital that we understand and manage the threats to this unique species.'