Juvenile recruitment of the Murray crayfish, Euastacus armatus (Decapoda:Parastacidae), from Southeastern Australia

The Murray crayfish (Euastacus armatus) is a large freshwater species endemic to the Murray-Darling River systems of South Australia, Victoria, New South Wales and the Australian Capital Territory, where it is important for recreational fishing and regional tourism. However, populations have continued to decline due to habitat modification and degradation, as well as overfishing. Further data on distribution, movements, habitat preferences and recruitment of juveniles are essential. To investigate the possibility of parental or offspring recognition, progressive levels of mortality were monitored in laboratory trials. In the short term (up to ∼ 8 days) there was reduced mortality in tanks where the adult was the mother, when compared to trials where the adult was unrelated. There was much lower mortality in tanks containing juveniles only. To assess prédation pressures, the presence and extent of juveniles in local fish diets was studied; analyses of gut contents revealed an annual peak in consumption among three native fish, which occurred in October, coincides with the release of juvenile E. armatus. To determine the potential for newly released juveniles to shelter within burrows, a small number of polyurethane foam casts were made; burrow features include a large entrance vestibule with smooth walls, leading into a short main tunnel with textured walls and one or two small branches. Very short-term parental protection after release and very limited burrow shelter, suggest that juveniles disperse within days of independence, which is consistent with the prédation data. Recommendations for the protection of juvenile populations included an increase in habitat complexity, through the natural accumulation of woody debris, and the addition of artificial shelters to shallow littoral zones < 2.0 m deep.