This study examined the occurrence, relative abundance and condition of platypuses in the upper catchment of the South Esk River, in north-east Tasmania, Australia, and the impact of past forestry activities on the occurrence of platypuses in first order headwater streams. The main trapping sites were in twenty first order streams, eight second-fourth order headwater streams and one fifth order stream reach. Additional trapping was also undertaken in the South Esk River and farm dams. Sites were trapped during late spring/mid summer and early autumn. A total of 78 individuals were caught in the study area. Platypuses were caught at all sites trapped in the second-fourth order and fifth order stream reaches and in nine of the twenty first order streams. Catch success was greatest in the fifth order stream reach and lowest in the first order streams. There was a trend toward a higher proportion of juvenile/subadult males in the lower order stream sites. For the higher stream orders, a higher proportion of individuals was caught during the summer, however for the first order streams, a higher proportion was caught during the autumn trapping period.Information collected on the body mass, body length and condition of individuals indicated smaller individuals with a higher tail fat index in the lower order streams.There was a trend toward a lower occurrence of platypuses in the first order streams, which had been disturbed 15 years previously by forestry operations compared to first order streams with relatively undisturbed catchments. Differences in occurrence of platypuses were related to differences in the 'instream' and riparian characteristics of disturbed streams compared to undisturbed streams. Headwater streams form a large proportion of a river system. Although they provide more marginal habitat for the platypus than larger river reaches, their disturbance may be an important land management issue in the conservation of this species, particularly in river catchments where the species is impacted by other environmental changes or disease.

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