Fish scale δ15N and δ13C values provide biogeochemical tags of fish comparable in performance to element concentrations in scales and otoliths

Abstract

Natural variability in stable isotope ratios and element concentrations in calcified structures of fish (e.g. scales and otoliths) has provided biogeochemical ‘tags’ for studying origins and movements of marine species, but has been little used in freshwater studies. We examine whether variability in scale δ15N and δ13C values of Salmo trutta L., could provide a tag of fish over small spatial scales in a small river catchment (River Dee, U.K.) and compared their performance as tags with that of scale/otolith element concentrations. Whole scale δ15N and δ13C values differed among six study sites and fish could be classified to their site of origin with a high degree of accuracy. Classifying fish to their site of capture was marginally superior using scale δ15N and δ13C values compared to that achieved using Sr, Mn, Ba and Mg in scale hydroxyapatite or otolith aragonite. Scale δ15N and δ13C values could therefore provide non-lethally collectable biogeochemical tags superior in performance to element concentrations in otoliths and scales. A comprehensive study of δ15N and δ13C values within freshwater systems would develop our understanding of factors influencing geographical variability in baseline δ15N and δ13C signatures.