AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 18–30 (2010) Published online 3 December 2009 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/aqc.1080 The impact of catastrophic channel change on freshwater mussels in the Hunter River system, Australia: a conservation assessment HUGH A. JONES a,b,Ã and MARIA BYRNE a a Department of Anatomy and Histology, Building F13, University of Sydney, NSW 2006, Australia b New South Wales Department of Environment, Climate Change and Water, PO Box 3720, Parramatta, NSW 2124, Australia ABSTRACT 1. Australia has a distinct suite of endemic freshwater mussel species, several of which are restricted to south- eastern Australia, an intensively modified region supporting much of the nation’s population and where pressures on freshwater ecosystems are increasing. 2. Surveys were made of 78 sites in the Hunter River system to determine the distribution and abundance of the six mussel species occurring in the region, to identify threatening processes and to locate populations of high conservation value. 3. Mussel populations were mainly distributed in the hydrologically stable southern Barrington rivers, where those in the Williams River have the highest conservation value. Strongholds for Hyridella drapeta were found in Wollombi Brook. 4. Mussels were not detected at 40% of the sites, some of which supported mussels in the past. These were mainly reaches that have undergone river metamorphosis. 5. Where found, most mussel populations had low densities and were highly fragmented. Major threats to these remnant populations are degradation of riparian and instream condition from agricultural activities, extreme climatic events (flood and drought) and the introduced macrophyte, Salvinia molesta. 6. While threat mitigation can be achieved by habitat protection and strategies to reconnect mussel populations, managers are largely unaware of this invertebrate group. Formal recognition of regionally threatened mussel populations would do much to focus efforts on conservation. 7. The proposed construction of a large dam on the Williams River is a potential threat to the most important mussel populations in the Hunter River system. Copyright r 2009 John Wiley & Sons, Ltd. Received 3 September 2008; Revised 27 August 2009; Accepted 29 August 2009 KEY WORDS: freshwater mussel species; freshwater ecosystems; distribution and abundance; disturbance; Hunter River system; regionally threatened mussel populations; Unionoida INTRODUCTION Freshwater mussels are major contributors to the biomass of lowland rivers, and through their filter-feeding activity play an important role in the functioning of river ecosystems (Strayer et al., 1994; Vaughn and Hakenkamp, 2001). In Australia, mussel populations have undergone declines due to river regulation and intensification of catchment land use (Brainwood et al., 2006, 2008a; Playford and Walker, 2008). This worldwide trend is associated with extinctions, as seen in the extensive loss of endemic mussel species in North America (Bogan, 1993). The disappearance of mussels from rivers in Australia is of concern from ecological and conservation perspectives (Byrne, 1998; Walker et al., 2001; Brainwood et al., 2006). The degeneration and fragmentation of freshwater habitats following urbanization and agricultural development of catchments has been identified as the major factor contributing to the global decline in freshwater biodiversity (Allan and Flecker, 1993). Intensification of catchment land use and river regulation (e.g. dams and river engineering) have profound impacts on river hydrology and geomorphology with consequent effects on the ecological integrity of these ecosystems (Poff et al., 1997, 2007; Gregory, 2006). Altered hydraulic conditions and reduced bed *Correspondence to: Hugh A. Jones, New South Wales Department of Environment, Climate Change and Water, PO Box 3720, Parramatta, NSW 2124, Australia. E-mail: hugh.jones@environment.nsw.gov.au Copyright r 2009 John Wiley & Sons, Ltd.