Changes in the distributions of freshwater mussels (Unionoida: Hyriidae) in coastal south‐eastern Australia and implications for their conservation status

The conservation of freshwater mussels is neglected in Australia, and poor historical data may mask trends in species’ range and abundance. A combined-evidence approach using published data, targeted surveys, historical records and a GIS-based, reach-scale measure of physical habitat quality was used to assess trends in the distributions of nine species in the south-eastern coastal region. Geomorphic impairment is widespread in upland and lowland streams, but not in rugged escarpment zones, with 16.8% of rivers in ‘poor’ geomorphic condition, 39.6% in ‘moderate’ condition and 43.6% of rivers in the region in ‘good’ condition. Reductions of 44.4, 12.5 and 39.7% in site occupancy over the past 200 years were estimated for Hyridella depressa, Hyridella drapeta and Hyridella australis from logistic regression models of occupancy versus river geomorphic condition. Nonetheless, all species remain widely distributed and qualify as ‘least concern’ according to IUCN Red List criteria. Hyridella narracanensis and Hyridella glenelgensis have fragmented or limited ranges and are vulnerable to threats, and both appear to meet IUCN Red List criteria for threatened species. The former species is listed as ‘data deficient’ but arguably should be ‘vulnerable’ as documented here. The latter species is not included on the IUCN Red List. Under the Australian EPBC Act (1999), H. narracanensis is not listed while H. glenelgensis is listed as ‘critically endangered’. The Tasmanian endemic, Velesunio moretonicus, shows some evidence of decline but its population status is equivocal owing to the lack of monitoring data. It would qualify as ‘data deficient’. The three remaining species, Cucumerunio novaehollandiae, Alathyria profuga and Velesunio ambiguus are widely distributed and show no evidence of decline. Additional surveys are needed to determine the current status and spatial distribution of freshwater mussel species in the region, and to establish baselines for future monitoring. Copyright © 2013 John Wiley & Sons, Ltd.