Astacopsis gouldi Clark: habitat characteristics and relative abundance of juveniles

A survey of juvenile Astacopsis gouldi was conducted in streams in northern Tasmania. Differences in catch per unit distance (CPUD) and catch per unit area (CPUA) of juvenile A. gouldi between stream classes (as defined in the Tasmanian Forest Practices Code) were examined, as well as relationships between CPUD, CPUA and habitat variables. Use of Class 4 streams (catchment area < 50 ha) by A. gouldi was consistently low compared to Class 2 streams (catchment area > 100 ha) in the stream systems studied, with A. gouldi occurring in only very low densities in Class 4 streams. Streams of 50-200 ha catchment area (stream Classes 2 to 3) and potentially those with significant and sustained groundwater input were found to be important for A. gouldi. Streams with less than 2% area of substrate as silt, high proportions of moss cover, moderate to high proportions (10-30%) of substrate as boulders, and channel slopes of less than 15% were associated with higher densities of juvenile A. gouldi. Meso-habitat features favoured by juvenile A. gouldi included large rocks or logs that overlie coarser substrates and/or which had a distinct cavity underneath. These characteristics of optimal habitat can be used to identify sections of stream drainage that may require local or upstream protection measures for juvenile A. gouldi.