There is debate in the literature as to whether scales of fishes require acidification to remove inorganic carbonates prior to stable isotope analysis. Acid-treated and untreated scales from 208 Atlantic salmon from nine locations on both sides of the Atlantic were analysed for δ 13 C and δ 15 N. Linear mixed-effect models determined the effect of acid treatment to be statistically significant. However, the mean difference was small (δ 13 C 0.1 ± 0.2‰, δ 15 N −0.1 ± 0.2‰) and not of biological relevance. This study concludes that Atlantic salmon scales do not need to be acidified prior to stable isotope analysis.