Sydney: The decline in platypus numbers in Australia has most likely been underestimated, according to new research from the University of NSW.

The platypus is listed as "near-threatened" on the International Union for Conservation of Nature Red List. Credit:Tamielle Brunt

The study, which examined data on the species from the past 258 years, has been published in the Global Ecology and Conservation journal.

It found changes to the species' distribution, with no recorded sightings of the mammal in more than 41 per cent of sub-catchments across its range in the past 10 years.

It also found considerable historical declines, with past accounts of platypus abundance that far exceed those of the present day.