|Scientific Name:||Euastacus dharawalus Morgan, 1997|
|Taxonomic Source(s):||Morgan, G.J. 1997. Freshwater crayfish of the genus Euastacus Clark (Decapoda: Parastacidae) from New South Wales, with a key to all species of the genus. Records of the Australian Museum Supplement 23: 1-110.|
|Taxonomic Notes:||Morgan (1997) named Euastacus dharawalus after the Dharawal aboriginal language, but did not designate an official common name. However, he did refer to specimens of Riek’s crayfish in the Australian Museum collection as Fitzroy Falls Crayfish. The common name Fitzroy Falls Crayfish has been used ever since. There are no recent taxonomic changes or doubts as to the species validity.|
|Red List Category & Criteria:||Critically Endangered B1ab(iii,v) ver 3.1|
|Contributor(s):||Furse, J., Coughran, J., 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.|
Euastacus dharawalus is assessed as Critically Endangered under B1ab(iii,v). The area of occupancy (AOO) and extent of occurrence (EOO) calculated following standard IUCN methodology are both 16 km². However, the actual EOO of this species is approximately 6 km² and it occupies habitat with an area of under 1 km². This species is known from a single location and a decline has been observed in both the quality of habitat and the number of mature individuals. These declines are attributed to lack of education, recreational fishing, alterations in the hydrological regime of headwater streams, predation by introduced fish species and competition from an introduced non-native species Cherax destructor. Additionally, the population has been divided by the construction of the Fitzroy Falls Reservoir and gene flow between the subpopulations has been permanently eliminated. This species faces a very real risk of extinction in the wild within the very near future.
|Previously published Red List assessments:|
|Range Description:|| |
The species is only know from Wildes Meadows Creek a tributary of the Kangaroo then Shoalhaven rivers, approximately 107 km south southwest of the Sydney Central Business District (CBD). The species was only known from two locations in one small stream less than 12 km long; one located in Wildes Meadow Creek above the falls and one above the reservoir, the total creek catchment area is 32 km² (McCormack 2013).
Native:Australia (New South Wales)
|Range Map:||Click here to open the map viewer and explore range.|
No quantitative data are available on the abundance of E. dharawalus, however, there are observational data from preliminary crayfish surveys.
Firstly, there is information on the population below the reservoir: a section of stream approximately 750 m long. Australian Crayfish Project (ACP) original surveys in 2006, 2007 and 2008 indicated a static population of approximately 1/10 lineal metre (l.m.) of stream. This would equate to a population estimate of 100 individuals. However, all individuals sampled during the 2008 survey displayed injuries consistent with aggressive competitive or predatory interactions with other crayfish (Coughran et al. 2009). The latest survey (late 2011) indicated a dramatic reduction in this population to 1/80 l.m. of stream. The reason for this dramatic reduction in population is unknown but of concern (McCormack 2013). This section of stream is suitable for mature individuals, it varies in width from two to six metres, an average width of four metres for the entire 750 m length equates to an area of occupied habitat of 0.003 km².
Secondly, there is information on the section of stream represented by the reservoir. This section of stream approximately 3 km long and has been inundated by the construction of a dam on Wildes Meadow Creek, creating an impoundment known as the Fitzroy Falls Reservoir. Fitzroy Falls Reservoir has a surface area of 5.2 km². Surveys of the reservoir indicate that E. dharawalus does not utilize lentic waters and is restricted to flowing stream conditions (McCormack 2013).
Thirdly, E. dharawalus occurs upstream of the reservoir. This prime large adult habitat area is the section of stream from the reservoir and approximately 2 km upstream. The stream varies in width from two to three metres, this equates to an area of occupied habitat of 0.005 km². Large adult individuals were approximately at 1/6 l.m. of stream length. This equates to an estimated adult population of less than 350 adult individuals. The next 2 km of stream seem suitable for smaller adults and juvenile crayfish. The stream here varies in width from one to two metres, this equates to an area of occupied habitat of 0.003 km². Here the smaller individuals were in higher densities at 1/2.5 l.m. of stream length. Here adults were approximately 25% of those capture the balance were immature, this equates to approximately 200 mature adults and 600 large immature individuals. The balance of the stream and all the smaller feeder streams are suitable for juvenile individuals. The adults utilize the deeper permanently flowing water. Surveys of the smaller headwater and ephemeral streams produced mostly juvenile individuals at relatively low densities of 1/2-5 l.m. of stream length.
The total adult population would be estimated at under 1,000 mature individuals, with approximately 600 mature individuals in the larger subpopulation above the dam and 10 mature individuals in the smaller subpopulation below the dam. Sixty percent of the prime available habitat area lost by the construction of the Fitzroy Falls Reservoir. The area of occupied habitat for mature individuals is 0.011 km². Applying the standard IUCN methodology based on a 2 x 2 km grid, the area of occupancy (AOO) is 16 km². The total extent of occurrence (EOO), calculated using a minimum convex polygon around collection sites, is 6 km². However, following the standard IUCN methodology the EOO should be increased to 16 km² to match the AOO.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:|| |
Euastacus dharawalus only occurs in Wildes Meadow Creek above Fitzroy Falls. Fitzroy Falls drops 81 metres into Yarrunga Creek which drains to the Kangaroo River and then the Shoalhaven River. Only Euastacus yanga Morgan, 1897 was found below the Falls and within Yarrunga Creek (McCormack 2013).
The ACP surveys of the region indicate that adult E. dharawalus inhabit the prime stream habitats needing deeper permanently flowing water and juvenile crayfish are restricted to smaller shallower feed streams. The main/prime large adult habitat area is a section of stream approximately 2 km long with the next 2 km of stream being suitable to smaller adults and juveniles. Additionally there is an intricate lacework of small drains, channels, creeks and stream that feed into Wildes Meadow Creek, much of this represents suitable juvenile habitat. The species does not occur in the 50 or so rural farm dams and ponds in the catchment or the main Fitzroy Falls Reservoir.
The majority of the catchment has been cleared for agriculture and the small feeder streams drain through grazing paddocks. Juvenile E. dharawalus construct burrows along the stream back and these are easily collapsed by grazing cattle and the ferns and bushes sheltering the creeks are grazed off by the cattle creating dangerous and unsuitable habitat.
|Continuing decline in area, extent and/or quality of habitat:||Yes|
|Generation Length (years):||9|
|Use and Trade:||The species is fully protected by government regulations. No trade or commercial utilization of the species is allowed.|
The Fitzroy Falls Reservoir with a water surface area of 5.2 km² was created in 1974 to supply water to the city of Sydney and its construction has dramatically altered the stream in which E. dharawalus lives. Approximately 3 km or 60% of the adults prime creek habitable area was destroyed by the construction of the dam or 25% of the total habitat area. The creek system has been divided by the construction of the reservoir. As E. dharawalus does not inhabit the reservoir the 3 km section of reservoir water acts as a permanent barrier between the upstream and downstream subpopulations. The physical barrier of the dam wall and the discharge of water from the reservoir to the stream below via a steel pipe inaccessible to crayfish ensures there is no possibility of gene flow between the fragmented subpopulations. The long term consequences of this subpopulation isolation and obstruction of gene flow are unknown (McCormack 2013).
Additionally, this is traditionally a rural farming area with rich soils and amenable climate. The majority of the upstream habitat area has been cleared for agriculture and the smaller feeder streams dammed by rural farm dams further limiting the available habitat area and restricting water flows to the feeder streams. Much of this upstream catchment area is comprised of streams meandering through grazing paddocks. We observed stream beds and banks degraded by stock trampling with numerous hoof-marks, increased turbidity and we expect increased nutrient concentrations in these streams. Banks and burrows were collapsed by hoofmarks and stream riparian vegetation was grazed all creating dangerous habitat for Euastacus crayfish (McCormack 2013).
The problems for E. dharawalus have been further increased by stocking of the reservoir with recreational fishing species. Rainbow Trout (Oncorhynchus mykiss), Australian Bass (Macquaria novemaculeata) and Carp (Cyprinus carpio) are all in the reservoir and are all known predators of crayfish. Introduced trout and any offspring that may now occur naturally pose a serious threat to E. dharawalus (Horwitz 1990, Merrick 1995). Adult crayfish are invulnerable to Trout predation but juveniles are susceptible. It is unknown the level of threat as interactions have not been recorded, but we know that trout prey on small juvenile freshwater crayfish and prefer a flowing stream environment the same as E. dharawalus. Site 028 on Wildes Meadow Creek where large numbers of large E. dharawalus where recorded, many with eggs, that would release small juveniles in that section of stream is a well-known recreational trout fishing area and referred to by the Sydney Catchment Authority (SCA) as a trout breeding section of stream (McCormack 2013).
Carp (Cyprinus carpio) is a large introduced freshwater fish which are common throughout most of NSW. It is well known as a pest because of its destructive bottom-feeding habits, which stir up sediments and muddy the water (NSW DPI Fisheries 2015). Carp is an omnivore consuming a broad range of foods including crustaceans (Allen et al. 2002). Australian Bass (Macquaria novemaculeata) is a known predator of small freshwater crayfish with recreational fishers traditionally using small crayfish as bait. These non-endemic species are a new threat to E. dharawalus and something that they have not evolved with, posing a serious and continuing threat to the survival of juvenile crayfish.
Fitzroy Falls Reservoir has been annually stocked with approximately 5,000 Rainbow Trout every year between 2005 and 2012. Additionally, 15,000 Australian Bass were stocked in 2013 (NSW DPI 2015).
The Yabby (Cherax destructor) has also been introduced into Fitzroy Falls Reservoir and Wildes Meadow Creek and is found above and below the reservoir. Cherax destructor is a native of the Murray Darling Basin and is not native to Wildes Meadow Creek. Euastacus dharawalus attains an OCL of 86 mm and weight of 300 grams (McCormack 2008). Cherax destructor can attain a size of 81 mm OCL and weigh 350 grams (McCormack 2008), so both species can attain a similar size and compete for the same food sources. The impacts of translocated populations of C. destructor in other areas of Australia have been discussed by various groups (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). The Yabby is a robust species with a broad environmental tolerance. It is robust and fast growing, maturing in as little as four months, and mature females direct most of their energy into reproduction (Wingfield 2002). Repetitive spawning is common, and females may brood up to three times in a breeding season (Rankin 2000, Wingfield 2002, McCormack 2005). Conversely, E. dharawalus are slow growing taking approximately five to nine years to mature. The females only breed once per year with long incubation times (approximately five months) and not all females breed each year. Coughran et al. (2009) first suggests that the reproductive traits of the Yabby equip it to outcompete the endemic Fitzroy Falls crayfish. Cherax destructor prefers the open sky cleared streams and lentic waters of ponds and dams making the altered habitat preferable to the translocated species.
The NSW Fisheries Scientific Committee has listed ‘The introduction of fish to fresh waters within a river catchment outside their natural range’ as a Key Threatening Process (KTP) under the Fisheries Management Act 1994 (FM Act). The Yabby is included in the definition of ‘fish’ under the FM Act and hence the impact on native freshwater crayfish would be covered by the existing KTP (Leishman pers. comm. 2012, Gilligan pers. comm. 2012, McCormack 2014).
The huge crayfish resource created by the proliferation of C. destructor throughout the reservoir and associated creeks generates an attractive resource for recreational fishers. Surveys, using standard recreational fishing methods over a one hour duration, captured over five kilograms of crayfish. Capturing C. destructor from the system is not the problem. The problem is that both E. dharawalus and C. destructor are captured together and it is not easy to distinguish the two species. The majority of recreational fishers may not be able to distinguish the two species and may take, remove and kill E. dharawalus (McCormack 2013). Recreational fishing must be considered a serious threat.
An insidious threat is the introduction and proliferation of Thelohania that is common in most C. destructor populations throughout Australia. Thelohania is a microscopic, microsporidian parasite that is a single celled parasite that spreads its infection by spores that increase in numbers in the muscle until the muscle appears white. In surrounding creeks to the east both Euastacus hirsutus and C. destructor are captured together. Thelohania infected E. hirsutus have been captured from the next two creeks east (Barrengarry and Dharawal creeks). These two records of infected Euastacus are the only ones in the ACP collection containing several thousand specimens of Euastacus (McCormack 2013).
Euastacus dharawalus was listed in November 2011 as a “Critically Endangered Species” by the NSW Fisheries Scientific Committee, making it the first Euastacus species in Australia to be listed as Critically Endangered under any State or Federal Government conservation legislation. In 2015 Euastacus dharawalus was nominated at a Federal Level for inclusion in the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), list of threatened species.
Protection of existing remnant riparian vegetation and encourage the restoration of riparian vegetation along the upper catchment streams and through the grazing paddocks. Together with stock fencing from the stream banks would do much to increase the survival of juvenile crayfish and convert the habitat to suitable for endemic species and less suitable to introduced C. destructor.
Prohibiting the construction of additional farm dams in the Wildes Meadow Creek catchment is recommended. Further removal of surface run-off into feeder streams can only be detrimental to juvenile survival. This prohibition may also need to be extended to farm water wells, as lowering groundwater in underground aquifers within this catchment could have devastating consequences for juveniles in the feeder streams and general stream flows.
Euastacus dharawalus does not inhabit the still water of farm dams preferring the flowing stream conditions. However, the still waters of dams is the preferred habitat of introduced C. destructor a species listed as a Key Threatening Process (KT) in NSW. Thus the existing dams create a constant infection source annually producing vast numbers of crayfish which can migrate into the feeder streams both upstream and downstream of the farm dam. Research needs to be conducted on the existing farm dams within the catchment area with an objective of seeking ways to limiting the C. destructor threat from these existing dams.
Instigation of a total recreational fishing ban on all streams with allowance only within the impoundment and well away from any stream mouths should be pursued. Exclusion of the general public from streams should be a priority. The section of stream below the reservoir within the National Park (with picnic tables and fishing access) should be closed and/or the stream fenced to prohibit recreational fishers. It is recommended that the stream be conserved as a visual asset rather than a recreation fishing resource vulnerable to plunder. Additionally, the section of stream upstream of the reservoir at the intersection of Church Street and Wildes Meadow Road (currently open to recreational fishers) should be closed off and fenced. Recreational fishing signs should be removed and closure signs erected. It should be noted that recreational fisher only targeting fish are not the problem, they are actually assisting the crayfish by removing the fish that eat the crayfish. Perhaps there could be restrictive fishing for approved and registered anglers that are educated on the importance of the crayfish and will to assist in their protection.
Lack of education of both the general public and regulatory personnel on the species present within the Wildes Meadow Creek is threat to this Critically Endangered species. Currently there are no guidelines or educational material to alert recreational fishers to the presence of E. dharawalus or how to distinguish it from the extremely common recreational fishing species C. destructor. It is recommended signs be erected and educational material made readily available.
Fish stocking needs serious consideration and subject to further research. Stocking with Australian Bass will help reduce Carp and Yabby problems, but it may also be a problem to juvenile E. dharawalus. Bass however, would generally be restricted to the reservoir and the sections of Wildes Meadow Creek where large adult crayfish occur that would be invulnerable to bass predation. Bass generally will not travel far upstream into shallower water. However, ongoing monitoring and research would be required to ensure unanticipated consequences don’t eventuate.
Most of the fish problems may be easily remedied by the installation of a fish barrier at the mouth of the creek. A sonic bubble barrier, electric fish barrier or something similar may stop fish from leaving the reservoir and entering the creek system. This would need very careful investigation to ensure no unanticipated consequences for the crayfish but a project well worthy of further research.
The instigation of a Carp control program (Industry and Investment NSW 2010) within the reservoir may help reduce Carp numbers and if the numbers are reduced the Carp problem may stay in the reservoir without large numbers of Carp venturing into the creek to seek food resources.
Trout also generate problems, with Brown Trout (Salmo trutta) and Rainbow Trout (Onchorhynchus mykiss) being carnivores and known to consume small freshwater crustaceans (Merrick and Schmida 1984). Trout currently stocked into the reservoir would not be restricted to the reservoir and could travel well up into Wildes Meadow Creek posing a serious threat to juvenile crayfish. It is our recommendation that all trout stocking cease.
Chemical usage in the Fitzroy Falls area is common and needs investigation. The pesticides Grazon Extra, Roundup Biactive, Brush Off and MCPA are applied to control the following weeds: blackberry, broom, pampas grass, fire weed, eucalypt and other regrowth, willows, exotic grasses and environmental weeds. Many of these weeds occur along the stream banks where E. dharawalus occur. Frontera et al. 2011, found that the major ingredients commonly found in herbicides (glyphosate acid and polyoxyethylenamine (POEA)), when Cherax quardricarinatus was exposed at relatively low rates resulted in slowed body-weight gain (growth). It is imperative to develop safe usage of chemical management plans for the streams in the area and this needs to be disseminated to all local property owners within the catchment area as well as local government and management agencies.
The potential to rejuvenate the section of stream between the reservoir and the Falls should be investigated. The only water that enters the stream is discharged from the dam and this section of stream provides an ideal test area for any conservation strategies and if the threats can be eliminated from this section of stream there is a potential for a protected species refuge within the National Park.
|Citation:||McCormack, R.B. 2016. Euastacus dharawalus. The IUCN Red List of Threatened Species 2016: e.T153704A82384910.Downloaded on 26 September 2018.|
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