Estimating survival of the tayatea astacopsis gouldi (crustacea, decapoda, parastacidae), an iconic, threatened freshwater invertebrate

Populations of the world’s largest freshwater invertebrate Astacopsis gouldi (tayatea, or giant Tasmanian freshwater crayfish) have declined because of land use changes and poaching. The species is endemic to northern Tasmania and is listed as ‘‘vulnerable’’ under the Commonwealth of Australia Environment Protection and Biodiversity Conservation Act of 1999 and the Tasmanian Threatened Species Protection Act of 1995. Mark–recapture models were tested for their suitability in estimating survival of a population of A. gouldi in a remote river. Tayatea were marked with passive integrated transponder (PIT) tags during a 7-mo period. Catchability of tagged and untagged A. gouldi was size and sex specific. Larger animals and females were more readily trapped throughout the sampling period, which spanned the austral autumn/winter. Catchability of male tayatea increased during May, and was strongly influenced by environmental conditions such as water temperature and river level. Results suggest that PIT tagging combined with mark–recapture methods are a feasible approach for estimating survival in tayatea, given sample sizes that can be achieved with reasonable effort. Precision of estimates could be improved by concentrating sampling around peak catchability during spring and autumn, and minor flood conditions during winter. This method provides a tool to estimate A. gouldi mortality as a result of illegal fishing and detrimental land use practices, thus providing better information for management. This strategy is essential to monitor progress toward the milestone of reducing their ‘‘vulnerable’’ classification under the Commonwealth and Tasmanian legislation within 14 y (1 generation) from the implementation of the plan.