Application of population size structure indices to Arctic charr Salvelinus alpinus (L.) in Alpine lakes in Austria

Abstract –  Stock density indices are numerical population descriptors derived from length-frequency data and has been mostly applied to North American sport fish populations to define the structure of the population. Traditional relative-stock-density and proportional-stock-density-indices were applied to Arctic charr, Salvelinus alpinus (L.) populations of five alpine and three prealpine Austrian lakes. Biological parameters of asymptotic size and size at maturity were used to define the length categories for the index calculation specifically for the lakes under study. We tested both, a ‘traditional approach’ and a ‘lake specific approach’. The results showed that the ‘lake specific approach’ provided a better insight to population structures of landlocked Arctic charr populations. In contrast, the ‘traditional approach’ gave an uninformative description of the population structures. Advantages and disadvantages of the techniques, applications and the results of the study lakes are discussed.