Estimating age composition in Alpine native populations of Austropotamobius pallipes complex

Understanding the population structure and growth of native freshwater crayfish is crucial to management freshwater resources and to solve fundamental questions of population conservation. In four mountain streams populated by Austropotamobius pallipes species complex, water temperature data were collected along a year period or more by data-loggers storing the value at 2 hours intervals. Crayfish samplings were conducted in July 2012 by night; their total (TL) and cephalothorax lengths (CL) were measured to the nearest mm; and weight and occurrence of mutilations were recorded. On the whole 746 crayfish were collected. Females and males distributions were analysed separately for each population. CL length data were used to generate histograms of polymodal frequency distributions; then they were decomposed using Bhattacharya’s Method, included in the FAO-ICLARM Stock Assessment Tools (FISAT) software. After hatching periods were assessed by using water temperature data according to degree-days required to birth time, age was assigned to each length class. The mean values of the age classes were used to evaluate the growth rate of Von Bertalanffy, by the seasonalized equation. Up to six age classes were identified in two populations. Results show three out four populations are well-structured and they confirm that A. pallipes complex is a k-selected species, with a slow growth rate (0.17 and 0.19 for males and females, respectively) showing evident seasonality in both sexes. We stress the great usefulness of these results in the monitoring and conservation plans of endangered crayfish.