Murray River Crayfish
Murray River Crayfish. Photo: M. Jekabsons, ACT Government.
The Murray River Crayfish is the second largest freshwater crayfish in the world and at risk of extinction unless actions are taken to conserve the species and protect its habitat.
Also known as the Murray Crayfish, Murray Lobster and Mungola, the Murray River Crayfish (Euastacus armatus) was listed as a vulnerable species in the ACT in 1997. It is listed as vulnerable in NSW, threatened in Victoria and protected in South Australia.
The crayfish lives in the southern Murray–Darling Basin below about 700 metres above sea level.In our region it lives in the Murrumbidgee River, lower Cotter River below the Cotter Dam, Tumut River, Goobragandra River and lower Goodradigbee River. It was occasionally seen in the Cotter River at Bracks Hole and may still occur within the new Enlarged Cotter Reservoir. It is no longer seen in the Molonglo, Queanbeyan and Yass rivers.
Murray River Crayfish like to live in permanent rivers and large streams where the water flows moderately fast. In the ACT, they burrow in amongst boulders and cobble and use tree ‘snags’ for cover. They mainly feed on woody debris, biofilms and leaf litter but also fish and animal carcasses. Because they shred large woody and leafy debris while eating, they help the aquatic nutrient cycle.
Murray River Crayfish can be up to 50 centimetres long and weigh 2.7 kilograms, but are usually less than half this size. They can live more than 30 years. Mature females mate in May and carry up to 1500 eggs under their tail through winter, only releasing the juveniles in late spring or early summer.
Freshwater crayfish and their habitats are imperilled globally, and the Murray River Crayfish is no exception. The major threats are habitat destruction or modification, river regulation, overfishing, alien species, disease, barriers to passage and climate change.
Although fished by Indigenous Australians for thousands of years, commercial fishing from the 1920s to the 1970s in NSW resulted in significant population decline, as did recreational fishing in the ACT. A fishing ban was introduced in 1991, however no significant changes in abundance have been observed and unfortunately illegal angling and overfishing still remain a threat.
Crayfish are sensitive to water quality and sediment addition, thermal pollution, pollutant discharges and bushfire impacts. Sediment from roads and construction sites, rural land uses and extreme events such as fires and floods damage water quality, cover habitat and change river flow.
Development can increase urban water run-off, change water quality, add sediment and alter the riparian vegetation. Weirs and dams slow water, which can impact on the crayfish’s habitat and breeding cycle.
The crayfish are eaten by predatory pest species such as Redfin and Carp and large native fish. If non-native or non-local crayfish (for example, alien yabbies used in aquaculture and aquaponics systems) enter the crayfish habitat they could compete with the crayfish, eat them or introduce disease. Imported live crayfish can carry fatal diseases and fungi.
Climate change puts the crayfish at risk. The predicted increase in summer storms and frequency of bushfires means the thermal cues (a drop in water temperature in autumn) used by the crayfish to initiate breeding may change. The species has already been lost from downstream warmer areas of the Murray–Darling Basin in South Australia.In addition, wildfires increase the risk of ‘blackwater events’ due to ash and fire debris run-off.
The overall conservation objective of the Murray River Crayfish Action Plan is to maintain viable, wild populations of Murray River Crayfish as a component of the indigenous aquatic biological resources of the ACT and as a contribution to regional and national conservation of the species. These actions will be driven by the Murray River Crayfish Action Plan (2018) and the ACT Aquatic and Riparian Conservation Strategy (2018).
Because of its vulnerability to extinction, it has been prohibited to take the Murray River Crayfish from ACT waters since 1991.
The ACT Government is contributing to improving riparian habitat for many native species, including the Murray River Crayfish through:
- replanting on the Murrumbidgee River as part of the Million Trees program
- improving aquatic habitat in the Upper Murrumbidgee Demonstration Reach (the 100 kilometre stretch of river from Bredbo to Casuarina Sands)
- establishing rock groynes and engineered log jams to rehabilitate fish habitat and improve fish passage through the sand slug in the Murrumbidgee River past Tharwa
- providing environmental water flows to improve the crayfish’s habitat conditions.
The action plan outlines how we can:
- protect the species from harvest
- protect sites in the ACT where the species occurs—protecting and revegetating riparian zones will improve food supply, provide shade which buffers water temperatures, provide cover, prevent erosion and filter sediment from run-off; minimising sediment addition will protect pools and maintain habitat in and around rocks and boulders
- manage habitat to conserve populations (for example, by maintaining riverine habitats with appropriate seasonal water flow regimes, intact riparian zones, minimal sediment and pollution from roads, urban areas and surrounding land use)
- enhance the long-term viability of populations through management of aquatic habitats, alien fish species, connectivity, stream flows and sedimentation in Murray River Crayfish habitats and areas next to themto increase habitat area and, where possible, connect populations
- improve understanding of the species’ ecology, habitat and threats through survey, monitoring and research.
- improve community awareness and support for the crayfish and freshwater fish conservation in general.
The plan also calls for the import and keeping of introduced crayfish to be prohibited to prevent diseases and potential competitors becoming established in the ACT.
- Murray Crayfish Action Plan, 2018
- Aquatic and Riparian Conservation Strategy, 2018
- NSW Government information