Effects of ethanol storage and lipids on stable isotope values in a large mammalian omnivore

Ethanol storage and lipid extraction can alter the isotopic composition of animal tissues, which can bias dietary estimates calculated by stable isotope mixing models (SIMMs). We examined the effects of ethanol storage and lipid extraction on δ13C, δ15N, and δ34S values measured in brown bear (Ursus arctos) muscles and livers. We also used isotopic data from our experiment to understand the effect of ethanol storage and lipid extraction on dietary contributions calculated by SIMMs. We found that ethanol storage and lipid extraction caused small increases in δ13C values for both muscles (ethanol storage: +0.4 ± 0.5‰, lipid extraction: +0.4 ± 0.4‰) and liver (ethanol storage: +0.6 ± 0.3‰, lipid extraction: +0.8 ± 0.5‰). In contrast, δ15N and δ34S values did not change when stored in ethanol or when lipids were extracted from tissues. Ethanol storage and lipid extraction had negligible effects on estimated dietary contributions. We show that a relatively high lipid content in the muscles and livers of some large-bodied terrestrial omnivores do not necessarily have an effect on dietary estimates that rely on carbon stable isotopes. Our results suggest that ethanol storage could be a valuable alternative method for preserving animal tissue prior to stable isotope analysis when freezing or drying is impractical. Nevertheless, further research is needed on the mechanisms that control changes in stable isotope composition in tissues stored in ethanol. We recommend investigating the effects of ethanol on stable isotope values in species and tissues of interest before storing samples in ethanol.