Juvenile recruitment of the Murray crayfish, Euastacus armatus (Decapoda: Parastacidae), from south-eastern Australia
Alves, N., Merrick, J.R., Kohen, J. and Gilligan, D., 2010. Juvenile recruitment of the Murray crayfish, Euastacus armatus (Decapoda: Parastacidae), from south-eastern Australia. Freshwater Crayfish, 17: 167–175.
The Murray crayfish is a large freshwater species native to the Murray-Darling River system, where it is important for recreational fishing. Populations have declined over several decades due to habitat modification and degradation as well as overfishing. Aspects of juvenile biology are an important knowledge gap for this species. Juveniles have typically been absent or under-represented in all existing studies on the species. A potential explanation may be that juvenile crayfish remain in their mothers burrow for the first year or two of life. If this were the case, we would expect some degree of parent-offspring recognition and perhaps parental care, and we would expect that juvenile crayfish would be uncommon in the diets of predatory fish because they would be sheltered in burrows and not exposed to predators.
To investigate the possibility of parental care in Murray crayfish, the levels of mortality immediately after dispersal (due to cannibalism) were monitored in laboratory experiments. In the short term (up to ~ 8 days) there was reduced mortality in offspring housed with their mother than for offspring housed with unrelated adult females. But there was much lower mortality again in those tanks containing only juveniles.
To determine the potential for newly released juveniles to shelter within the burrow of their mother, we made a small number of foam casts from wild Murray crayfish burrows. Burrow features include a large entrance chamber with smooth walls, leading into a short main tunnel with textured walls and one or two small branches.
To assess predation pressure in wild populations, we studied the presence and extent of juveniles in local fish diets in the Murrumbidgee River. Analysis of gut contents revealed an annual peak (October) in consumption of juvenile Murray crayfish in three native fish species. This peak coincides with dispersal period of juveniles.
Together, these observations suggest that juvenile Murray crayfish disperse within days of independence and forage in the open where they are exposed to predation by fish. Therefore, it does not appear that the absence of juvenile crayfish from existing datasets was a result of them being restricted to surviving within burrows for the first few years of their life. The lack of juvenile crayfish in existing datasets must be because the sampling tools used to collect adult crayfish are inefficient for sampling juveniles, or that juveniles have very specific habitat requirements that differ from those of adults. Further work on developing sampling strategies for collecting juvenile crayfish and subsequent studies into the habitat requirements of juveniles are required.