The study included the free-flowing Ovens River and the dammed Mitta Mitta River, both in north-east Victoria.
The study found that large dams were significant barriers to platypus movements.
This was reflected in greater genetic differentiation between platypus above and below large dams, compared to rivers without dams.
Importantly, this genetic differentiation increased over time since the dam was built, reflecting the long-term impacts of the dam.
“We extracted the DNA from the blood collected by our Platypus Conservation Initiative researchers at UNSW,” study lead author Dr Luis Mijangos said.
“By using thousands of molecular markers, we were able to identify a strong signal indicating that genetic differentiation increased rapidly between platypuses below and above these large dams.”
Professor Richard Kingsford, another of the paper’s authors, said the finding had significant implications for platypus conservation.
“We’ve long suspected that prey can restrict platypus movements, but this is the ‘smoking gun’,” Prof Kingsford said.
“These animals just can't get around big dams.”
Platypuses whose movements are restricted by large dams have limited or no gene flow with other groups, making these separate populations increasingly vulnerable to threats.
There was increased possibility of inbreeding depression, loss of adaptive genetic variation, failure to recolonise areas where local extinctions had occurred, and failure to disperse to areas with more suitable conditions, the study said.
“We know that platypuses are declining in many parts of their range in eastern Australia, affected by many threats. This study identifies one of the main threats to this iconic species,” another of the authors, Dr Gilad Bino, said.
The authors recommended that water conservation and management planning should consider alternative approaches to large dams.
These could include storing water in off-river reservoirs and implementing strategies to reduce the effects of dams, such as the artificial relocation of individual platypus between groups above and below dams, or the construction of passage structures that increase dispersal.
The study was published in the international journal Communications Biology.
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