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 predator 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.