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Westralunio carteri

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA HYRIIDAE

Scientific Name: Westralunio carteri
Species Authority: Iredalei, 1944
Common Name(s):
English Carter’s Freshwater Mussel
Taxonomic Notes: Conventionally accepted as Westralunio carteri (Iredale, 1934). There have been no recent changes to its taxonomy (Walker et al. 2013);

Iredale (1934) referred to two subspecies: Westralunio ambiguus ambiguus and Westralunio ambiguus carteri. McMichael & Hiscock (1958) recognised Westralunio carteri as a single taxon to avoid confusion with Velesunio ambiguus, a widespread species from eastern Australia.

Older synonyms include:
  • Unio australis Menke, 1843;
  • Unio moretonicus E.A. Smith, 1874;
  • Hyridella ambigua Cotton & Gabriel, 1932;
  • Centralhyria angasi subjecta Iredale, 1934;
  • Westralunio ambiguus carteri Iredale, 1934; Iredale, 1943;
  • Westralunio ambiguus ambiguus Iredale, 1934; Iredale, 1943.
Recent investigations have indicated that juveniles of this species possess shell sculpturing on their umbos, which may assist in further refinement of morphological keys and may result in higher level taxonomic re-alignment in the future (Zieritz et al. 2013).

This species is the sole representative of the genus in Australia, with two other Westralunio species occurring in New Guinea (McMichael and Hiscock 1958, Walker et al. 2013). The evolutionary relationship between the three species is currently unknown and their description is based primarily on adult shell characters.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2c ver 3.1
Year Published: 2014
Date Assessed: 2014-04-07
Assessor(s): Klunzinger, M & Walker, KF
Reviewer(s): Lopes-Lima , M. & Seddon, M.B.
Contributor(s): Beatty, S., Keleher, J., Kirkendale, L., Lymbery, A., Morgan, D., Pinder, A., Robert, J., Slack-Smith, S. & Whisson, C.
Justification:

Westralunio carteri is restricted to south-western Western Australia, and occurs in 13 of 18 river basins in the South West Coast Drainage Division. Where the species occurs, subpopulations are found within 100 km of the coast. Some subpopulations have declined or have experienced catastrophic mortality leading to loss of entire subpopulations caused by increased water salinity, physical destruction of habitat and reduced river flows (hence stranding and possible predation by mammals).

The species is assessed as Vulnerable (VU A2c), based on an overall suspected population decline of >30% over the last three generations (ca. 58-87 years). The decline is estimated from local extinctions in three of the 16 river basins where the species formerly occurred and declines in six of those remaining, where the species is restricted to non-salinized tributaries or lower reaches of main river channels.

The threats to the species are known and increasing.

History:
2011 Least Concern
1996 Vulnerable

Geographic Range [top]

Range Description:

Westralunio carteri is restricted to south-western Australia.

Based on museum records, this species has a former range extending from the Moore River in the north to King George Sound in the south and inland to the Avon River (museum records; Iredale 1934, 1943; McMichael and Hiscock 1958; Kendrick 1976; Storey and Edward 1989; Williams et al. 1991)

The current distribution is restricted to freshwater streams, rivers, reservoirs and lakes within 50-100 km of the coast within south-western Australia from Gingin Brook southward to the Kent River, Goodga River and Waychinicup River  (Edward et al. 1994; Growns and Davis 1994; Bennet-Chambers et al. 1999; Lymbery et al. 2008; Sommer et al. 2008; Walker et al. 2013; Klunzinger et al. 2012a,b, 2014a,b).

The current extent of occurrence is estimated to have declined by 49% over the last three generations (ca. 60 years). 

Countries:
Native:
Australia (Western Australia)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Current population size is not available. Some subpopulations have declined from catastrophic mortality (e.g., salinity, physical destruction of habitat, exposure to air and possibly predation by introduced mammals).

Where suitable habitats remain in ‘good’ condition, the species can still be found in relatively dense patches (20-50 individuals/m²), but seldom >100 mussels/m² overall population trend is decreasing as threats continue (Klunzinger et al. 2012b, 2014b).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology:

Life Cycle/Dispersal:

  • Sexes separate, hermaphroditism rare;
  • Spawning = winter (June-August)
  • Fertilisation occurs in specialized chambers of females’ gills, known as ‘marsupia’;
  • Embryos brooded in marsupia
  • Mature larvae ‘glochidia’ released in strings of mucus, cued by temperature change and increased day length (late-August – December/early-January)
  • Females barren or remainder of the year
  • Glochidia attach to fish gills or fins and encased in a cyst for 3-4 weeks while undergoing metamorphosis to juvenile form;
  • Following parasitic period, metamorphosed glochidia (i.e. juveniles) detach to begin life in the sediments (no change in shell length while on the fish);
  • Adults capable of moving distances of 7-10 m over a long period of time, but generally sedentary.
  • Glochidia parasitism of fishes is thought to be a dispersal mechanism.
  • W. carteri is a host fish generalist.

(Kendrick 1976; Morgan et al. 2011; Klunzinger et al. 2012a,b, 2013, 2014a; Walker et al. 2013)

Host Fish (Klunzinger et al. 2012a)
Confirmed host fish species:

Native Fishes: Tandanus bostocki Whitley, 1944; Nannoperca vittata (Castelnau, 1873); Afurcagobius suppositus (Sauvage, 1880); Pseudogobius olorum (Sauvage, 1880); Bostockia porosa Castelnau, 1873; Galaxias occidentalis Ogilby, 1899; Leptatherina wallacei (Prince, Ivantsoff & Potter, 1982)

Introduced Fishes: Gambusia holbrooki (Girard, 1859); Phalloceros caudimaculatus (Hensel, 1868)     

Unsuitable host fish species:
Introduced Fishes: Carassius auratus Linnaeus, 1758

*Note:  An additional seven introduced and three native fishes that occur in parts of the geographic range of W. carteri remain untested as host fishes. Those listed above are the most widespread.

Age at sexual maturity: 3-6 years (Klunzinger et al. 2014a)

Life expectancy: at least 36‑52 years (Klunzinger et al. 2014a)

Habitat requirements:

  • Freshwater lakes, rivers and streams (mean salinity <1.6 ppt);
  • Patchy distribution in sandy/muddy sediments with greatest densities associated with exposed submerged tree roots (Eucalyptus rudis, Melaleuca spp. and others), woody debris and overhanging riparian vegetation near stream banks and edges of lakes/dams;
  • Precise habitat requirements and quantification of density within habitat types are in the early stages of study for this species;  juveniles may require specific micro-habitats and are difficult to locate in the wild.

Systems: Freshwater

Use and Trade [top]

Use and Trade:

According to early European accounts by Sir George Grey, in his book entitled ‘A Vocabulary of the Dialects of South Western Australia’ (Grey 1841), the Nyoongar name used for this species was probably either ‘Inbee’ or ‘Marailya’ which he described as being “a species of Unio, generally called the fresh water mussel.  The natives of this part of Australia will not eat them, having a tradition, that many years ago some natives were poisoned by them; but to the north-west part they are a favourite article of food. Europeans about the Swan River occasionally eat them, and I have made several hearty meals from them.”

Although his account may be accurate for the Nyoongar individuals he spoke with, it is most likely they were men and traditionally this species was woman’s tucker (personal communication with individuals of the Nyoongar community). There may have also been different names used for the species depending on which Nyoongar language group they are located in. Oral tradition is maintained by elders within each Nyoongar language group and a full account of the traditional knowledge of this species should be sought through the appropriate cultural protocols and Indigenous Engagement agencies such as the South West Aboriginal Land and Sea Council, Department of Aboriginal Affairs, South West Catchments Council or others.

Threats [top]

Major Threat(s):

Known Threats:
The following threats are known to have occurred in the past, are current and likely to continue into the future

Primary threats
Salinity:  Salinity tolerance experiments indicated LC50 limits of 1.3 – 3.0 ppt and LC95 limits of 3.2 – 4.3 ppt and no W. carteri were found alive in systems in which average salinity was >1.5 ppt (Klunzinger et al. 2010).  It is well established that the salinity problems in south-western Australia are primarily a result of rising groundwater from extensive clearing (Mayer et al. 2005). More than 90% of Western Australia’s original vegetation has been cleared since European settlement (Bradshaw 2012), with the trends continuing and more thinning and clearing for urban development and timber harvest planned for the future (CCWA 2014). This, coupled with a drying climate suggests salinisation caused by land clearing will continue to be a problem into the future.

Dewatering:  Dehydration resulting from reduced flow and artificial removal of water from regulated rivers and dams have led to mortalities of 17-25% (Klunzinger et al. unpublished data). In dehydration tolerance experiments, W. carteri was unable to withstand extreme drying without shade for more than five days (Klunzinger et al. 2014b).

Secondary threats
Habitat destruction:  Livestock and humans are known to be causing destruction of habitat, sedimentation and erosion and trampling on live W. carteri, resulting in death.

Environmental tolerances:  Specific environmental tolerances have not been quantified except for salinity and dehydration. High water temperatures and nutrient pollution resulting in low dissolved oxygen and high ammonia concentrations may cause local population losses.

Loss of suitable host fishes: This species is a generalist in terms of host fish use by its glochidia for the completion of the species’ life cycle. However, introduced fishes (e.g., Goldfish) may not support the species’ life cycle. Not all species of fishes which occur throughout W. carteri’s range have been confirmed as competent hosts and this is an area for future study.

Impact of threats
Salinty and extreme dehydration (i.e., exposure to air, direct sunlight and lack of sheltering habitat) causes 100% mortality within a few days and may be immediate in some cases.

Low dissolved oxygen is known to cause abortion of glochidia in most species and has the potential to cause death over prolonged exposure periods in some species (Walker et al. 2013).

Trampling by cattle and motor vehicles are known to cause death.

Burying by deep loose sand or fine silty sediments are known to cause death in W. carteri (Klunzinger, pers. obs.).

Prolonged reduction in recruitment may lead to long-term population losses.

Other threats may include those listed for other Australian species (see Walker et al. 2013; Brainwood et al. 2006, 2008a,b; Jones and Byrne 2010, 2013; Klunzinger et al. 2014b).

Conservation Actions [top]

Conservation Actions:

There have been a few select threat abatement actions in localized subpopulations undertaken through environmental consultancies for state government agencies. However, the success of translocation strategies to mitigate impacts is unknown. Otherwise, there are currently no recovery or threat abatement/mitigation actions proposed or planned specifically for the species.


Citation: Klunzinger, M & Walker, KF 2014. Westralunio carteri. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 20 December 2014.
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