Carter’s freshwater mussel case study Freshwater mussels (Bivalvia: Unionoida) constitute one salinisation and reduced water flow from a drying of the most endangered groups of organisms climate (Klunzinger et al. 2015). It is patchily distributed throughout the world (Bogan, 2008; Walker et al., 2014; in freshwater streams, rivers, reservoirs and lakes within IUCN, 2016). 50-100km of the coast. Carter’s Freshwater Mussel Westralunio carteri is The species is classified as Vulnerable under the Wildlife unique in being the only species of freshwater mussel Conservation Act and EPBC Act and Vulnerable on the found in south-western Australia and the only member IUCN Red List of threatened species (Klunzinger & of the genus Westralunio in Australia. Walker, 2014). However until recently, almost nothing was known The species is now confined to non-salinised rivers and about the biology or conservation status of this species. streams mostly in forested catchments along the west and south coasts. The range of W. carteri has contracted by 49% in less than 50 years, principally as a result of secondary Carter’s Freshwater Mussel Westralunio carteri (Photograph: S. Beatty) SOUTH WEST SNAPSHOT This project is supported by the South West southwestsnapshot.com.au Catchments Council, through funding from the Australian Government’s National Landcare Program. Map 1: a) Current (post-1992) distribution of Westralunio carteri. Black circles indicate mussel presence; grey triangles indicate mussel absence. b) Historic (post-1992) distribution of Westralunio carteri. Black circles indicate mussels historically and currently present, grey squares indicate mussels historically present, but currently absent. c) Minimum convex hulls for current presence (P) data, historic (H) presence data and absence (A) data. Figure reproduced from Klunzinger et al. (2015). Map 2: Current extent of Carter’s Freshwater Mussel, according to ICUN redlist (data source: http://maps.iucnredlist.org/map.html?id=23073). SOUTH WEST SNAPSHOT This project is supported by the South West southwestsnapshot.com.au Catchments Council, through funding from the Australian Government’s National Landcare Program. Values Key threats Freshwater mussels are an important component of The threats to the species are known and increasing freshwater ecosystems as they are a filter feeding (IUCN, 2018). group removing sediment and pollutants from the Key threats to the species include ongoing secondary water (Idrisi et al., 2001; Caraco et al., 2006) thus salinisation, climatic drying and riparian degradation. having a positive effect on water quality. Population size reduction will be determined primarily While the filter feeding capacity of Carter’s Freshwater by salinity, which may exceed the maximum salinity Mussel have not been estimated, filtration rates of threshold of the species (2-3 ppt). other species can be up to 1.81 L/hr/g (dry weight of mussels). Additionally, reduction in flows or increased extraction could lead to extirpation if not managed appropriately. This means entire lakes can be filtered by mussel populations in a matter of days (Ogilvie and Mitchell Other threats are cattle trampling, predation by pigs, 1995; James et al., 1998). water extraction, dehydration and heat stress. Freshwater mussels can also bring other benefits to benthic and pelagic systems (Greenwood et al., 2001; Strayer, 2014). Interesting facts Call to action • Freshwater mussels can't move very far. So • Prevent any further deforestation and land the way they get around is by sticking their clearing in catchment areas where the species larvae on a fish and the fish takes it to a is present, particularly close to rivers and new habitat. creeks. • Carter’s Freshwater Mussel is the sole • The production of a recovery plan may benefit representative of the genus in Australia, the species for future management. with two other Westralunio species • Habitat protection adjacent to waterways occurring in New Guinea. including cattle exclusion. • Carter’s Freshwater Mussel reaches sexual • Maintain freshwater flow and groundwater maturity at a size of 25–30 mm long, at 2–3 discharge. years of age. Growth slows as they age and • Maintain shading riparian vegetation and the maximum recorded size for the species revegetate where necessary. is 101 mm long, but they are typically less • Avoid unnecessary water extraction and/or than 90 mm long. Age-at-length and growth mitigate impacts during rapid drawdowns rates are variable between populations, but within reservoirs. for the populations which have been validated, maximum ages range between • Reduce nutrient runoff and intercept nutrients 40 and 50 years old and ages of individuals before they enter the waterways. of the same size from different populations • Ongoing control of feral pigs. can vary by as much as 10 years. SOUTH WEST SNAPSHOT This project is supported by the South West southwestsnapshot.com.au Catchments Council, through funding from the Australian Government’s National Landcare Program. References Klunzinger, M. W., Beatty, S. J., Morgan, D. L., Pinder, A. M., & Caraco, N. F., Cole, J. J., & Strayer, D. L. (2006). Top-down Lymbery, A. J. (2015). Range decline and conservation status control from the bottom: Regulation of eutrophication in a of Westralunio carteri Iredale, 1934 (Bivalvia : Hyriidae) from large river by benthic grazing. Limnology and Oceanography, south-western Australia. Australian Journal of Zoology, 63, 51, 664-670. 127-135. Greenwood, K. S., Thorp, J. H., Summers, R. B., & Guelda, D. L. Klunzinger, M. & Walker, K. F. (2014). Westralunio carteri. The (2001). Effects of an exotic bivalve mollusc on benthic IUCN Red List of Threatened Species 2014: invertebrates and food quality in the Ohio River. e.T23073A58526341. Hydrobiologia, 462, 169-172. Ogilvie, S., & Mitchell, S. (1995). A model of mussel filtration in Idrisi, N., Mills, E. L., Rudstam, L. G., & Stewart, D. J. (2001). a shallow New Zealand lake, with reference to eutrophication Impact of zebra mussels (Dreissena polymorpha) on the control. Archives of Hydrobiology, 133, 471-481. pelagic lower trophic levels of Oneida Lake, New York. Mackie, G. L., & Claudi, R. (2009). Monitoring and Control of Canadian Journal of Fisheries and Aquatic Sciences, 58, 1430- Macrofouling Mollusks in Fresh Water Systems (2nd ed.). Boca 1441. Raton, FL: CRC Press. IUCN (2018). Downloaded: http://www.iucnredlist.org/ Strayer, D. L. (2014). Understanding how nutrient cycles and details/23073/0 freshwater mussels (Unionoida) affect one another. Hydrobiologia, 735, 277-292. James, M.R., Ogilvie, S.C., & Henderson, R. (1998). Ecology and potential use in biomanipulation of the freshwater mussel Hyridella menziesii (Gray) in Lake Rotoroa. NIWA Client Author Report HCC9020/1. Dr Stephen Beatty, Murdoch University Carter’s Freshwater Mussel in Cane Brake Pool, Margaret River (Photograph: S. Beatty) SOUTH WEST SNAPSHOT This project is supported by the South West southwestsnapshot.com.au Catchments Council, through funding from the Australian Government’s National Landcare Program. .