|Scientific Name:||Cherax tenuimanus|
|Species Authority:||(Smith, 1912)|
Chaeraps tenuimanus Smith, 1912
|Red List Category & Criteria:||Critically Endangered B2ab(ii,iii,v) ver 3.1|
|Assessor/s:||Austin, C.M. & Bunn, J.|
|Reviewer/s:||Collen, B. & Richman, N.|
|Contributor/s:||Livingston, F., Livingston, F., Soulsby, A.-M., Batchelor, A., Dyer, E., Whitton, F., Milligan, H.T., Smith, J., Lutz, M.L., De Silva, R., McGuinness, S., Kasthala, G., Jopling, B., Sullivan, K. & Cryer, G.|
Cherax tenuimanus has been assessed as Critically Endangered using criteria B1ab(ii,iii,v). This species is estimated to have an area of occupancy less than 10 km² and is found at a single location. There are a number of threats resulting in a continuing decline in this species range, number of mature individuals, and quality of habitat. The key threat to this species is hybridization with the Smooth Marron, Cherax cainii: evidence suggests as much as 10% of the population may be comprised of hybrids. Conservation measures, such as placing bans on fishing, have been employed to slow this rate of decline, however action needs to be taken with regards to preventing further hybridization.
|Range Description:||This species is restricted to the upper reaches of the Margaret River in the south-west of Western Australia (Morgan and Beatty 2005, Bunn 2004). This species is currently only known from 11 sites in an area less than 50 km in length (Department of the Environment, Water, Heritage and the Arts 2008). The area of occupancy (AOO) for this species is estimated to be less than 10 km² (Department of the Environment, Water, Heritage and the Arts 2008).|
Native:Australia (Western Australia)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This species has undergone a significant decline in population numbers within a very short period of time. Estimates indicate that there are possibly only 10,000 wild individuals left (Bunn 2004). In 2002, Austin and Ryan determined there had been an estimated 70% reduction in the numbers of this species in seven years at just one location, with a near 100% reduction in 13 years.|
|Habitat and Ecology:||This species is found in the deep waters of rivers on sandy stretches with plenty of organic matter. Individuals require access to shelter and refugia (e.g. rocks and tree roots), and good water quality (C.M. Austin pers. comm. 2008).|
The main threat to this species is direct competition with the Smooth Marron, Cherax cainii. The Smooth Marron has now replaced much of this species' former range in the lower and middle reaches of the Margaret River. Cherax tenuimanus is reported to hybridize with the Smooth Marron; 10% of the population at a location in the upper reaches of the river was comprised of hybrids (Bunn 2004). If Smooth Marron are considered the primary threat to this species, then the entire Margaret River system could be termed one location.
This species faces a number of threats in the middle and lower reaches of the river including habitat degradation, changes to the hydrological regime, predation by fish species (e.g. Redfin Perch) and competition (e.g. Smooth Marron and Yabbies), and illegal fishing activity targeting mature individuals (Department of the Environment, Water, Heritage and the Arts 2008).
The Threatened Species Scientific Committee have proposed that this species be listed as Critically Endangered and be noted as Threatened Fauna of Australia under the Environment Protection and Biodiversity Conservation Act 1999. Recreational fishing of this species has been prohibited above the 10 Mile Brook Junction (Molony et al. 2004). However, illegal fishing activity still occurs and many fishers find it difficult to distinguish between Smooth and Hairy Marron (Department of the Environment, Water, Heritage and the Arts 2008). A broodstock of Hairy Marron are being maintained at Pemberton Freshwater Research Centre for possible re-introduction programs. While re-introduction programs could result in increases in the population, this is only going to be maintained if other stressors are removed.
Conservation measures, as suggested by the Threatened Species Scientific Committee, include: removal of Smooth Marron from key habitat of the Hairy Marron, prevention of any further introductions of the Smooth Marron to the Margaret River, habitat maintenance, and re-introductions from the Pemberton broodstock.
|Citation:||Austin, C.M. & Bunn, J. 2010. Cherax tenuimanus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 18 May 2013.|
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