Background/Aims
Murray Crayfish is the second largest freshwater crayfish in the world. Once common in the waters of the South Australian River Murray, the number of Murray crayfish declined to a point of virtual extinction in the 1980s as a result of overfishing, the effects of river regulation and declines in water quality. Improved understanding and recent improvements to these conditions mean it’s now time to bring the species back to South Australia. Through this highly collaborative five year project, Murray crayfish adults and juveniles have been released to a restored section of the River Murray as part of a landmark trial to reintroduce the iconic Australian species back into the South Australian River Murray.
Methods
The reintroduction of Murray crayfish back into the South Australian section of the Murray River was guided by comprehensive planning (informed by a successful interstate reintroduction) to maximise the likelihood of success. Annual releases of 200 adult and 350 juveniles, reared in captivity, were undertaken. Acoustic telemetry and standard hoop net monitoring was undertaken to detect success of reintroductions. During acoustic telemetry, a subset of reintroduced Murray crayfish were fitted with accelerometer tags annually and released amongst an array of acoustic receivers to evaluate activity patterns.
Results
Monitoring reveals that thus far reintroductions have been successful. During hoop net monitoring, both adults and berried females were sampled in the reintroduction reach. Through the use of acoustic telemetry, over one million individual detections of the tagged crayfish (individual crayfish detections) were recorded and over 80% of tagged crayfish were detected. Variable activity between and within days (and between crayfish) and differing movement patterns were recorded, with most crayfish remaining within the reintroduction reach. However, larger movement was revealed in some crayfish.
Conclusion
The reintroduction of Murray crayfish back into the SA section of the Murray River represents one of the most significant reintroduction projects ever conducted in South Australia. Building on more than a decade of research and planning, this long term project provides the best possibility of re-establishment of a self-sustaining population of the species in South Australia.