Population structure and life history characteristics of the freshwater crayfish Gramastacus insolitus and Geocharax falcata (Parastacidae) in the Grampians National Park, Australia

Means by which freshwater crayfish persist in seasonally-dry wetlands are poorly understood, but this information is important for their management and conservation. This study examined the population structure, reproductive timing, and life history strategies of two Australian freshwater crayfish species that have a commensal relationship, through seasonal surveys conducted once in each season over 24 months. Gramastacus insolitus is able to achieve large population densities in ephemeral waterbodies but lacks the capacity to burrow, while Geocharaxfalcata can burrow to survive annual drying. Higher abundances were generally recorded in spring and summer than other times of year for both species. Sex ratios in G insolitus almost always favoured females, sexually mature females were 7.2 mm OCL or larger and gravid females were captured in the highest abundances in spring. Preparatory moulting, spawning, brooding of eggs and release of juveniles occurs in both species over the period of late winter to late summer. Both species have the life history characteristics of summer brooders such as: potentially asynchronous spawning regimes, short breeding periods, relatively short life spans, and the ability to grow rapidly. These traits demonstrate the flexibility required by freshwater crayfish to enable them to inhabit seasonally-dry wetlands where the timing and duration of inundation of these habitats is unpredictable. © 2010 International Association of Astacology.