This project is supported by the South West

Catchments Council, through funding from the

Australian Government’s National Landcare Program. southwestsnapshot.com.au

SOUTH WEST SNAPSHOT

case study

Carter’s freshwater mussel

Carter’s Freshwater Mussel Westralunio carteri

(Photograph: S. Beatty)

Freshwater mussels (Bivalvia: Unionoida) constitute one

of the most endangered groups of organisms

throughout the world (Bogan, 2008; Walker et al., 2014;

IUCN, 2016).

Carter’s Freshwater Mussel Westralunio carteri is

unique in being the only species of freshwater mussel

found in south-western Australia and the only member

of the genus Westralunio in Australia.

However until recently, almost nothing was known

about the biology or conservation status of this species.

The range of W. carteri has contracted by 49% in less

than 50 years, principally as a result of secondary

salinisation and reduced water flow from a drying

climate (Klunzinger et al. 2015). It is patchily distributed

in freshwater streams, rivers, reservoirs and lakes within

50-100km of the coast.

The species is classified as Vulnerable under the Wildlife

Conservation Act and EPBC Act and Vulnerable on the

IUCN Red List of threatened species (Klunzinger &

Walker, 2014).

The species is now confined to non-salinised rivers and

streams mostly in forested catchments along the west

and south coasts.

This project is supported by the South West

Catchments Council, through funding from the

Australian Government’s National Landcare Program. southwestsnapshot.com.au

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

Catchments Council, through funding from the

Australian Government’s National Landcare Program. southwestsnapshot.com.au

Interesting facts

• Freshwater mussels can't move very far. So

the way they get around is by sticking their

larvae on a fish and the fish takes it to a

new habitat.

• Carter’s Freshwater Mussel is the sole

representative of the genus in Australia,

with two other Westralunio species

occurring in New Guinea.

• Carter’s Freshwater Mussel reaches sexual

maturity at a size of 25–30 mm long, at 2–3

years of age. Growth slows as they age and

the maximum recorded size for the species

is 101 mm long, but they are typically less

than 90 mm long. Age-at-length and growth

rates are variable between populations, but

for the populations which have been

validated, maximum ages range between

40 and 50 years old and ages of individuals

of the same size from different populations

can vary by as much as 10 years.

Call to action

• Prevent any further deforestation and land

clearing in catchment areas where the species

is present, particularly close to rivers and

creeks.

• The production of a recovery plan may benefit

the species for future management.

• Habitat protection adjacent to waterways

including cattle exclusion.

• Maintain freshwater flow and groundwater

discharge.

• Maintain shading riparian vegetation and

revegetate where necessary.

• Avoid unnecessary water extraction and/or

mitigate impacts during rapid drawdowns

within reservoirs.

• Reduce nutrient runoff and intercept nutrients

before they enter the waterways.

• Ongoing control of feral pigs.

SOUTH WEST SNAPSHOT

Values

Freshwater mussels are an important component of

freshwater ecosystems as they are a filter feeding

group removing sediment and pollutants from the

water (Idrisi et al., 2001; Caraco et al., 2006) thus

having a positive effect on water quality.

While the filter feeding capacity of Carter’s Freshwater

Mussel have not been estimated, filtration rates of

other species can be up to 1.81 L/hr/g (dry weight of

mussels).

This means entire lakes can be filtered by mussel

populations in a matter of days (Ogilvie and Mitchell

1995; James et al., 1998).

Freshwater mussels can also bring other benefits to

benthic and pelagic systems (Greenwood et al., 2001;

Strayer, 2014).

Key threats

The threats to the species are known and increasing

(IUCN, 2018).

Key threats to the species include ongoing secondary

salinisation, climatic drying and riparian degradation.

Population size reduction will be determined primarily

by salinity, which may exceed the maximum salinity

threshold of the species (2-3 ppt).

Additionally, reduction in flows or increased extraction

could lead to extirpation if not managed appropriately.

Other threats are cattle trampling, predation by pigs,

water extraction, dehydration and heat stress.

This project is supported by the South West

Catchments Council, through funding from the

Australian Government’s National Landcare Program. southwestsnapshot.com.au

SOUTH WEST SNAPSHOT

References Caraco, N. F., Cole, J. J., & Strayer, D. L. (2006). Top-down

control from the bottom: Regulation of eutrophication in a

large river by benthic grazing. Limnology and Oceanography,

51, 664-670.

Greenwood, K. S., Thorp, J. H., Summers, R. B., & Guelda, D. L.

(2001). Effects of an exotic bivalve mollusc on benthic

invertebrates and food quality in the Ohio River.

Hydrobiologia, 462, 169-172.

Idrisi, N., Mills, E. L., Rudstam, L. G., & Stewart, D. J. (2001).

Impact of zebra mussels (Dreissena polymorpha) on the

pelagic lower trophic levels of Oneida Lake, New York.

Canadian Journal of Fisheries and Aquatic Sciences, 58, 1430-

1441.

IUCN (2018). Downloaded: http://www.iucnredlist.org/

details/23073/0

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

Report HCC9020/1.

Klunzinger, M. W., Beatty, S. J., Morgan, D. L., Pinder, A. M., &

Lymbery, A. J. (2015). Range decline and conservation status

of Westralunio carteri Iredale, 1934 (Bivalvia : Hyriidae) from

south-western Australia. Australian Journal of Zoology, 63,

127-135.

Klunzinger, M. & Walker, K. F. (2014). Westralunio carteri. The

IUCN Red List of Threatened Species 2014:

e.T23073A58526341.

Ogilvie, S., & Mitchell, S. (1995). A model of mussel filtration in

a shallow New Zealand lake, with reference to eutrophication

control. Archives of Hydrobiology, 133, 471-481.

Mackie, G. L., & Claudi, R. (2009). Monitoring and Control of

Macrofouling Mollusks in Fresh Water Systems (2nd ed.). Boca

Raton, FL: CRC Press.

Strayer, D. L. (2014). Understanding how nutrient cycles and

freshwater mussels (Unionoida) affect one another.

Hydrobiologia, 735, 277-292.

Author Dr Stephen Beatty, Murdoch University

Carter’s Freshwater Mussel in Cane Brake Pool, Margaret River

(Photograph: S. Beatty)