Juvenile Astacopsis gouldi in headwater streams - relative abundance and habitat

Abstract

Two surveys were conducted of juvenile Astacopsis gouldi in headwater streams. Repeated sampling of Class 4 and 2 streams in two drainage suggested that a string seasonal pattern in abundance was absent, and that use of Class 4 streams (as defined in the Forest Practices Code) was relatively low at all times of the year compared to Class 2 streams. A survey of a large number of relatively undisturbed stream sites indicated that: - Class 4 streams are used by juvenile A. gouldi, but at significantly lower densities than Class 2 streams; - juvenile A. gouldi numbers are highly spatially variable; - juvenile A. gouldi are more abundant in Class 2 streams of moderate catchment size, and wider channels. Macro-habitat features favoured by juvenile A. gouldi include: - wide streams with catchment areas typically 2 to 30 km2; < 2% area of substrate as silt; 10% high proportions of moss cover; moderate to high proportions (10 - 30%) of substrate as boulders; channel slopes < 15%; or - small streams of 0.4 to 2 km2 catchment area and with significant and sustained groundwater (spring) input leading to elevated perennial baseflows. Meso-habitat features favoured by juvenile A. gouldi include large rocks or logs that are big enough not to be easily dislodged, not embedded in finer substrates, that overly coarser substrates and/or with a distinct cavity underneath. The maintenance of current prescriptions for the protection of headwater A. gouldi populations is recommended.