Murray Spiny Crayfish (Euastacus Armatus)

Action Statement FloraFlora and Fauna and Guarantee Fauna ActGuarantee 1988 Act 1988 No. No. 184### Glenelg Spiny Crayfish Euastacus bispinosus Murray Spiny Crayfish Euastacus armatus Description and Distribution Thirty-three species of Australian Freshwater Australia has a diverse crayfish fauna with over crayfish are considered threatened, though 100 species in 10 genera. Crayfish belonging to few are recognised by State agencies (Horwitz the genus Euastacus are known as Spiny Crayfish 1995) while fourteen species of Euastacus have and belong to the Family Parastacidae. The genus been reported as requiring conservation Euastacus Clarke 1936 is found exclusively in attention (Horwitz 1995). eastern Australia with 41 species recognised Both spiny crayfish addressed in this Action (Morgan 1997). Ten Euastacus or spiny crayfish Statement, Euastacus bispinosus and E. are known from Victoria. As the name suggests, armatus, are large spiny crayfish and form the the genus is characterised by the presence of basis of a recreational fishery. All species heavy claws or chelae and spiny appearance have suffered declines in abundance and size (Zeidler 1982). This includes lateral spines, throughout their range, with E. armatus, the tubercules, and setal bumps on the abdomen. largest of the spiny crays, being the most Species can be identified by the number and notable example. Of the three species, E. position of these spines. bispinosus is thought to be the least abundant Despite the diversity of crayfish in Australia, very and has therefore been subject to more little is known about the biology and life history stringent fishing regulations (Barker 1990). of the group, apart from observations in Life History and Ecology taxonomic reviews (Merrick 1993; Morgan 1986, Spiny crayfish are very slow growing and can 1997). Detailed studies are confined to a few take up to 9 years to reach breeding maturity species that are significant in recreational (Honan and Mitchell 1995b, Turvey and fisheries or have commercial culture potential eg. Merrick 1997). Large specimens of Euastacus Cherax species (Merrick and Lambert 1991). spinifer (160 mm carapace length [CL]) can Most of the Euastacus group have restricted weigh up to 1.8 kg and have been estimated to distributions in the headwaters of streams along be up to 40 years old (Turvey and Merrick the east and south coast of Australia (Horwitz 1997). Similar findings for other Euastacus 1990). They generally inhabit flowing aerated, such as E armatus and E. bispinosus have been cooler streams, usually in hilly or mountainous recorded (Geddes 1990, Honan and Mitchell country. A few occupy lakes and impoundments 1995b). and occur in the more turbid and slower flowing Mating activity between mature crayfish waters of the Murray River System. occurs from May onwards each year, following Many members of the group have restricted which females carry eggs under the tail. The distributions and may be geographically isolated. eggs hatch from October onwards, depending This, in combination with habitat modification on seasonal conditions and the species. The and pressures from recreational fishing means dependent juvenile crayfish are carried that many of Australia’s freshwater crayfish are rare. beneath the tail for some weeks or months after The Murray River hatching. The yolk of the egg is retained by the Subject of extensive desnagging and salinity young hatchlings as a yolk sac supplying food problems. during early growth. Once the yolk sac has been The Glenelg River completely absorbed, the young disperse to fend for themselves. The Glenelg River catchment has been extensively cleared or modified and sedimentation occurs Freshwater crayfish are bottom-dwelling throughout the system (Mitchell 1990). The opportunistic scavengers. Their diet consists construction of the Rocklands Reservoir is thought largely of plant debris with the prime nutrient to have resulted in the local extinction of the source considered to be micro-organisms and fungi species, which were recorded from the site prior to that colonise on the detritus (Hogger 1998, Turvey the establishment of the dam (Horwitz 1990). E. and Merrick 1997). Most are moderate burrowers, bispinosus prefers streams with well vegetated, but many find refuge under rock ledges and shaded banks with an abundance of woody debris amongst submerged tree roots (Zeidler 1982). (Morgan 1983). Clearly, the loss of riparian Spiny crayfish activity is related to water vegetation represents a significant threat to the temperature, with most activity recorded between species. 8oC and 19oC (Barker 1990). Over-fishing Declines and Threats Over-fishing has contributed to the decline of Habitat alteration and destruction is widely many native aquatic species such as Macquarie recognised as one of the most significant causes of Perch (Maccullochella macquariensis) (Cadwallader aquatic species decline (Koehn and O’Connor 1990, 1978; Harris and Rowland 1996) and Murray Cod Campbell and Doeg 1989). Species with limited (Maccullochella peelii peelii) (Rowland 1989; distributions and fragmented populations, Jackson et al. 1994). Over-fishing has been combined with biological features which contribute recognised as a threatening process for the Murray to low recruitment rates, are particularly Spiny Crayfish (E. armatus) in NSW (Geddes, 1990), vulnerable to localised environmental ACT (Lintermans and Rutzou 1991) and South disturbances. Major threats to Spiny Crayfish Australia (Horwitz 1990a, Lintermans and Rutzou include habitat modification and manipulation of 1991, Lintermans 1998) and the Giant Tasmanian waterways resulting in reduced water quality and Lobster (Astacopsis gouldi) (Horwitz 1994). habitat fragmentation and pressure from over fishing. Predation by introduced fish such as trout Concern for spiny crays in the 1980s arose from may also be a threat. anecdotal reports by anglers that crayfish sizes and abundance had decreased markedly over time Riparian vegetation is important for bank (Horwitz 1990b). While fishing regulations were in stabilisation, as a filter for contaminants, in place, prior to 1989 there was no size limit on particular sediment and as a source of organic spiny freshwater crayfish and anglers were debris which provides energy in addition to permitted to retain all size of crayfish captured. instream habitat (Koehn and O’Connor 1990). Removal or modification of this vegetation has There is little data available which examines the serious consequence for the water quality and response of crayfish to over fishing. Morey (1987, hence habitat quality of waterways. Light intensity 1998) examined the success of fishing restrictions and stream temperatures may also be altered by on Gippsland Spiny Crayfish E. kershawi by removal of shade sources, particularly in summer. investigating the catch and growth rates of the species in open (no catch restrictions) and closed Impacts associated with stock and supply of water waters of the Bunyip and La Trobe River systems for domestic and irrigation uses are considered respectively. Overall, there was no significant threatening processes. This includes siltation, difference between the catch rates of crayfish from alteration of flows through irrigation and weir closed waters compared with open waters, nor construction, and loss of aquatic plants through were any differences in growth rates found. Morey turbidity. (1998) concluded that illegal fishing during the Desnagging and clearing streams decreases the closure accounted for similarities in catch numbers habitat available to crayfish by removing shelter between open and closed waters. This is supported and protective areas for juvenile crayfish to by the finding that very low catch rates were develop. Sediment deposition in streams may also observed at sites that were easily accessible such be detrimental to young crayfish as it coats the as picnic sites, roadsides and bridges. Fish substrata and fills interstitial spaces. These areas monitoring programs in the Murrumbidgee River in may be of value in protecting juvenile crayfish the mid 1990s after recreational fishing in the ACT from predators. was closed in 1991, indicated that there was some recovery of E. armatus (ACT Government 1998). 2 Data now available on the biology several larger and Rainbow trout (Onchorhynchus mykiss) are Euastacus species indicate that these crayfish have known predators of crustaceans and have been similar life cycles including slow growth rate and implicated as threats to some freshwater crayfish late maturation, long life span, and low fecundity species. Eels are also known predators of crayfish with annual breeding (Honan and Mitchell (Merrick 1995). 1995a,b,c; Morey 1998). These characteristics make Euastacus have been recorded as the preferred diet them vulnerable to over-exploitation by fishing, of foxes in some areas (Green and Osborne 1994) heightened when combined with the stresses of and thus fox predation may represent a threat to fragmented populations, habitat loss and the species in areas where foxes are prevalent. degradation (Horwitz 1990a). For example, the Glenelg Spiny Cray species is slow growing and may take up to 12 years to reach reproductive Existing Conservation Measures maturity. It is long lived, reproduces annually, has a low dispersal rate and is found in low densities Controls over fishing (Honan and Mitchell 1995a,b,c). Morey (1998) • The Flora and Fauna Guarantee (Taking or recorded a growth rate of 7mm per year for E. Keeping of Spiny

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