Euastacus clarkae 


Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Arthropoda Malacostraca Decapoda Parastacidae

Scientific Name: Euastacus clarkae
Species Authority: Morgan, 1997
Common Name(s):
English Ellen Clark’s Crayfish
Taxonomic Notes: Morgan (1997) named the species "in respect of Ellen Clark’s pioneering parastacid studies".

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(iii)+2ab(iii) ver 3.1
Year Published: 2015
Date Assessed: 2015-06-12
Assessor(s): McCormack, R.B.
Reviewer(s): Crandall, K.A.
Contributor(s): Furse, J. & Coughran, J.
Euastacus clarkae is assessed as Endangered. This is based on an extent of occurrence (EOO) of 198 km2, an area of occupancy (AOO) of 68 km2, occurrence at one to two threat-based locations, and an anticipated decline in area, extent and/or quality of habitat due to climate change.
Previously published Red List assessments:
2010 Critically Endangered (CR)

Geographic Range [top]

Range Description: The geographic range of E. clarkae is restricted to headwater reaches of highland streams draining the plateau and feeding the Hastings and Forbes rivers, at elevations ranging from 670-1,150 m asl (McCormack 2014). Both the Hastings and Forbes rivers are connected without any obstruction separating the rivers. Rainbow Trout or the invasive Cherax destructor once introduced to either the Hastings or the Forbes rivers could devastate that drainage and then easily move between drainages and infest the other as well. Both trout and Cherax destructor disperse widely throughout systems. As a result, there are one to two threat-based locations as it would take only one or possibly two introduction events for these invasive species to spread throughout the drainage system (R.B. McCormack pers. comm. 2015).
Countries occurrence:
Australia (New South Wales)
Estimated area of occupancy (AOO) - km2: 68
Number of Locations: 1-2
Lower elevation limit (metres): 670
Upper elevation limit (metres): 1150
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Although E. clarkae has a restricted distribution, it is present in reasonably high numbers in suitable streams. The species is locally abundant within suitable streams.
Current Population Trend: Stable
Additional data:

Habitat and Ecology [top]

Habitat and Ecology: Euastacus clarkae is restricted to headwater reaches of highland streams draining the plateau and feeding the Hastings and Forbes rivers, at elevations ranging from 670-1,150 m asl within Werrikimbe National Park. The species inhabits pools and riffles in small permanent streams. The larger adults occupy the better habitat areas (deeper pools) whilst the smaller juveniles are restricted to shallow water and riffles. It only establishes populations in permanently flowing streams that have a catchment starting above 900 m asl (McCormack 2014). Horwitz and Richardson (1986) classified Australian freshwater crayfish burrows based on their relationship to the water-table, into three categories (Type 1-3). 
  • Type 1 Burrows in or connected to permanent waters
  • Type 2 Burrows connected to the water-table
  • Type 3 Burrows independent of the water-table
Euastacus clarkae constructs a burrows system in response to the location and maturity of the burrow builder, however, all burrows would be within the “Type 1” category with all burrows in, or connected to open/flowing water (McCormack 2015).
Systems: Freshwater
Continuing decline in area, extent and/or quality of habitat: Yes

Use and Trade [top]

Use and Trade: The species is fully protected by Government regulations. No trade or commercial utilization of the species is allowed.

Threats [top]

Major Threat(s): Over 95% of the species distribution is within Werrikimbe National Park where habitat degradation from logging and development is not a threat.

Exotic pests such as cats, foxes, pigs and goats occur within the range of E. clarkae. These species have been found to impact on other crayfish species elsewhere (e.g. Green and Osbourne 1981, Horwitz 1990, Merrick 1995, Eyre et al. 1997, ACT Government 2007, O’Brien 2007). Feral pigs are the most significant threat to crayfish as their digging degrades habitat causing erosion, silting streams and weed infestations. Research found no evidence of predation on E. clarkae by pigs: “The feral pigs in the area are controlled by an annual trapping and shooting program in winter. The pigs have been there for decades, and go up and down in population, but the densities are never particularly huge in comparison to what you find out west” (P. Thomas (National Parks and Wildlife Service (NP&WS)) pers. comm. 2015). Extensive surveys recording feral pigs and small areas of ground disturbance in the area did not document any habitat degradation likely to impact E. clarkae or any indications of species interactions (McCormack 2015). Therefore, feral pigs are not considered a threat to E. clarkae.

McCormack (2015) did not detect feral goats and they remain unrecorded by the National Parks staff (P. Thomas (NP&WS) pers. comm. 2015).

Foxes and feral cats have been recorded in the area (McCormack 2015). However, there was no indication of any interaction whatsoever with E. clarkae and these two threats are considered to be insignificant (R.B McCormack pers. comm. 2015).

Freshwater crayfish are a common species targeted by recreational fishers in New South Wales. Over-harvesting is a major threat to slow growing, uncommon, protected species like E. clarkae. Due to lack of education, recreational fishers illegally harvesting E. clarkae, which is easily caught in crayfish traps, can quickly eliminate them from creeks.

Exotic Rainbow Trout (Oncorhynchus mykiss) is a known predators of freshwater crayfish (Horwitz 1990, Merrick 1995). Introduced trout and any offspring that may now occur naturally pose a serious threat. Adult crayfish are invulnerable to trout predation but juveniles are susceptible (Merrick and Schmida 1984). The level of threat is unknown as interactions have not been documented, but it is known that trout prey on small juvenile freshwater crayfish and prefer the same upland, flowing stream environments as E. clarkae. Trout were observed in the same pool as a berried female E. clarkae in an unnamed tributary of Dingo Creek, crossing Werrikimbe Trail, Werrikimbe National Park. These juveniles once released would be extremely susceptible to predation. The upper reaches of the Hastings River are not currently regarded as a well-known recreational trout fishing area and fortunately the numbers of trout in the streams are currently low.

Tadpoles are common in crayfishes diets (Turvey and Merrick 1997, Dorne and Wojdak 2004, McCormack and Coughran 2011). There is also a potential threat from Cane Toads (Rhinella marina) (NSW OEH 2014b) whose tadpoles and eggs are poisonous (Grace 2008). However, there are no specific data on impacts of Cane Toad tadpoles on E. clarkae. McCormack (2015) did not record cane toads and they have not been recorded in Werrikimbe National Park (P. Thomas (NP&WS) pers. comm. 2015), although Cane Toads have been recorded from the lower Hastings drainage: “The western outskirts of suburban Port Macquarie had a small outbreak of Cane Toads in early 1996. Approximately 400 were removed over 10 years in partnership with NPWS, Port Macquarie-Hastings Council and Port Macquarie Landcare. Final eradication was with the use of a trained Cane Toad sniffer dog brought in from WA. The outbreak area has been filled and is now part of an urban subdivision” (T. Aaso (Port Macquarie-Hasting Council) pers. comm. 2015). Predicted climate change will likely increase this threat, plus the species is currently moving approximately 3-4 km/year south in NSW (NSW OEH 2014a).

The negative impacts from translocated populations of Cherax destructor in other parts of Australia have been discussed by various authors (Austin 1985, Horwitz 1990, Horwitz and Knott 1995, Merrick 1995, Elvey et al. 1996, Bradsell et al. 2002, Beatty et al. 2005, Coughran et al. 2009, McCormack 2013, McCormack 2014). Although C. destructor is proliferating in some coastal rivers of eastern NSW none have been recorded within the EOO of E. clarkae or elsewhere in the Hastings drainage (McCormack 2014).

The restricted highland distribution of E. clarkae probably indicates a requirement for cool conditions (Horwitz 1990, Morgan 1991, Ponniah and Hughes 2004), and therefore climate change is considered a major threat to E. clarkae. The original IUCN Red List assessment by Furse and Coughran (2010) considered climate change a significant threat. Euastacus clarkae is highly likely to be vulnerable to increases in water temperature and reductions in hydrological stability/security as it only occurs in the perennial flowing streams with a catchment starting at 900 m asl or above. It is surrounded by other crayfish species that occupy a broader range of habitats and water temperatures such as E. spinifer and E. spinichelatus. Hence any climate change that increases water temperatures and or reduces stream flows will impact on E. clarkae, reducing its population size and compacting its distribution whilst favouring its congeners. Unfortunately, as a species adapted to the highest elevations and cool environments it will have nowhere to retreat to as the climate warms.

Bushfires although a natural part of the Australian landscape have proven to be a significant threat to this species with mass mortality being recorded after a bushfire. On 9 October 2013, a lightning strike started a bushfire north of the Kunderang Brook crossing on the Racecourse Trail. By 17 November 2013 the bushfire was declared out having burnt 13,500 hectares of Werrikimbe and Willi Willi National Parks. This was the first time in 20 years that section of park has burnt, and it was entirely a natural event (P. Thomas (NP&WS) pers. comm. 2015). Surveys of a tributary of the Forbes River beside Racecourse Trail, Werrikimbe National Park on 16 February 2014 discovered large numbers of dead crayfish. Site 28 is a permanent micro-stream flowing down a gentle slope through a shallow, broad depression. The micro-stream is c. 0.2-1 m wide with a swampy floodplain either side c. 3-6 m wide. Crayfish burrows extend from the creek and across the flat swampy floodplain. Burrows in the creek bed where water is openly flowing belong to E. clarkae while those away from the flowing water area on the flood plain either side belong to E. maccai. Normally the area would be densely covered in reeds and grasses growing in this lush swampy area but the fire stripped the area to bare soil. In February we found large numbers of shells from dead crayfish scattered along the sides of the micro stream and up to six metres from the stream. There were approximately 40 deaths per 50 m of lineal stream length. Only E. clarkae shells were present, not one E. maccai shell was recorded. All shells were unburnt, indicating that death occurred after the fire. Additionally, grass/plants were regrowing through some shells indicating that death occurred sometime before the survey. According to R.B. McCormack (pers. comm. 2015), Euastacus crayfish in Type 1 burrows connected to shallow, slow flowing creeks are at high risk during a major bushfire from the creek water which can rapidly rise in temperature significantly stressing or killing the crayfish. The bushfire was the direct cause of this mass mortality (R.B. McCormack pers. comm. 2015). As global warming generates more hot weather leading to increases in the Forest Fire Danger Index (Steffen et al. 2014) severe bushfires are more likely, and so cases of mass mortality where the entire local population is devastated such as this are likely to be more common.

Conservation Actions [top]

Conservation Actions: There are no specific conservation measures in place for E. clarkae in NSW. NSW Fisheries has a total ban on the capture of small Euastacus spp. Consequently, all small intermediate group Euastacus spp. are protected by default in NSW since they do not reach the minimum recreational fishing size limit of 9 cm OCL (NSW DPI 2014). Additionally, the use of crayfish traps in eastern drainage rivers of NSW is prohibited offering some protection. Nonetheless, the species is still vulnerable to illegal fishing and capture in illegal traps. Lack of education continues to be a major problem in NSW as far too many recreational fishers are unable to distinguish between yabbies’ (Cherax) which are a legal recreational species and spiny crayfish (Euastacus spp.). Ignorance of the fishing regulations and of the diversity of Australian crayfish continues to be a major problem for the conservation and management of Australian Euastacus. The Australian Crayfish Project volunteers will advocate and lobby for the extension of the Werrikimbe National Park (WNP) boundaries to be expanded to include the small section of Mount Boss State Forest in which E. clarkae is known to occur. This parcel of land needs to be included in the National Parks and Wildlife Service (NP&WS) list of future acquisitions. Additionally, signage should be erected at all camping areas within the National Park advising of the presence of rare crayfish and their protection within the park. Both these measures will contribute to the conservation of the species and will be submitted as recommendations to NP&WS. In the meantime it is recommended that the distribution area within Mount Boss State Forest be declared a significant environmental area and request a 50 m buffer zone each side along the creek (McCormack 2015).

Any future conservation or management initiatives for E. clarkae will be greatly facilitated by further research. This should include an assessment of population genetics, an investigation of habitat requirements, biology and life history, investigation of thermal tolerance; base line monitoring of stream temperatures and resilience to exotic species. Ongoing monitoring of the species is required to maintain knowledge of its status and identify any declines. The development of a specific conservation program for the endangered E. clarkae in future WNP management plans is important given that almost the entire distribution is contained within WNP. Much of the population is located in rugged sections of the National Park and difficult for the general public to find or access. Nonetheless, within the National Park and adjoining State Forest there are areas open to the general public containing camping areas on streams that contain populations of E. clarkae. It would be in the interest of the conservation of this slow-growing species to erect signage and supply information alerting the public to its protected status.

Citation: McCormack, R.B. 2015. Euastacus clarkae. The IUCN Red List of Threatened Species 2015: e.T153666A79360699. . Downloaded on 26 November 2015.
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