Geographical Variation in the Giant Freshwater Crayfish, Astacopsis gouldi: Deductions from a Large Opportunistic Database

An on-going opportunistic tagging program marked almost 600 giant freshwater crayfish, Astacopsis gouldi, between 22-222 mm carapace length from 123 localities on 62 rivers in Tasmania since 1998. Eighty animals were recaptured once, 50 more than once, and the longest period between initial and latest capture was 8 years. These data were analysed to examine differences in size and growth between the sexes, between the disjunct eastern and western ranges of the species, and between catchments on nutrient-poor and nutrient-rich rocks. Male animals were heavier per unit length than females, as were animals from the western part of the range compared to the naturally disjunct eastern range. Males grew slightly faster than females. Animals from a catchment underlain by nutrient-poor quartzite rocks grew more slowly than those in a neighbouring catchment on richer dolerite. Individual growth histories varied considerably and suggest that there may be fast-growing and slow-growing animals within the population.