Using historical data to highlight population declines in the iconic Australian platypus

Abstract

Long-term population data is essential for accurately assessing species status and for the correct management of endangered species. However, not all species are easily monitored and have been historically overlooked, giving inadequate data to form population estimates. Analysis of historical data is a relatively new technique for conservation management, often providing long-term population changes which would be otherwise undetectable using contemporary ecological monitoring. In this study we investigated long-term population changes for the iconic Australia platypus (Ornithorhynchus anatinus), by collating 257 years of historical data from newspaper archives, museums, natural history books, explorer journals and national Atlas data (1760-2017). The platypus is the most evolutionarily distinct mammal alive today, being the only member of the Ornithorhynchidae family and one of only five extant monotreme species that exist worldwide. The semi-aquatic mammal is endemic to creeks and rivers in eastern Australia and is threatened by river regulation and degradation, crayfish netting, predation, and pollution across its range. Despite the evolutionary uniqueness of the platypus, surprisingly little is known about its conservation status. The nocturnal and cryptic nature of the platypus, and the scarcity of long-term monitoring studies, has limited our capacity to assess changes in distribution and abundance, both historically and in more recent research. Thus, the conservation status of ‘near threatened’ (IUCN), and ‘least concern’ (Australian state legislation), may not reflect the true ecological status of the platypus. Our historical analyses suggest historical platypus abundances far exceeded current observations. Further, our comprehensive assessment of distributional change suggests a range decline for the platypus. Periods of decline and low population numbers have resulted in an intergenerational loss of knowledge on platypus abundances, leading to the perception that these lower contemporary abundances are representative of baseline populations. This study highlights long-term declines in platypus populations, essential information for accurately assessing the conservation status of the platypus and for future management strategies of this declining iconic Australia mammal.