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Little is known of the current status of platypus (Ornithorhynchus anatinus) populations in the Murrumbidgee catchment and other west-flowing rivers in the Murray–Darling Basin. Platypus distribution in the Murrumbidgee catchment was determined from sightings, reports by government departments, the literature and a capture–release study. The platypus was found to be widespread in the catchment, including all subcatchment and elevation categories, but most reports were from the middle and upper subcatchments. Sixty-five captures of 55 individual platypuses were made during 61 trap-nights to 31 study sites in the Murrumbidgee catchment during 2009–10. Only three juveniles (all females) were captured and recapture rates were low, with only nine platypuses captured more than once. Adult males had body weights of 980–2180 g and body lengths of 42–60 cm (n = 32). Adult females weighed 795–1480 g and were 38–52 cm long (n = 20). Tail fat index was significantly affected by season and platypus age, while in comparison, season, platypus length and weight had a significant effect on tail volume index. This study established a baseline that provides a starting point from which the impacts of environmental disturbances or diseases occurring over time can be measured and investigated.

Over a twelve month period, 25 platypuses (Ornithorhynchus anatinus) were presented for necropsy. The most common causes of mortality were dog predation (40%), road trauma (28%), starvation and/or exposure (16%) and Mucor-mycosis (8%). Mucor amphibiorum is the only disease agent known to cause significant morbidity and mortality in free-living O. anatinus in Tasmania. This fungus causes a severe, granulomatous, commonly ulcerative, skin condition in this species. A study was conducted to define the nature and extent of the granulomatous dermatitis caused by M. amphibiorum. The mycotic granulomatous dermatitis of O. anatinus appears to be confined to streams in the north and midlands. The prevalence of the disease at two infected sites was 36% (n=36) and 66% (n=3). Lesions included abscesses, ulcers, granulation tissue and nodules. Of the 17 diseased animals captured, II were adult male, 5 were adult female and 1 was a juvenile female. Thirteen isolates of M. amphibiorum were cultured from skin lesions, all were of the positive mating type. Mucor amphibiorum was not isolated from 40 faecal or 8 skin samples from O. anatinus. No M. amphibiorum was isolated from 14 environmental samples. Mucor circinelloides and M. saturninus were isolated from soil, and M. circinelloides and M. hiemalis were isolated from faecal samples from O. anatinus.