How to use live sampling tissues and archived specimens in cetacean stable isotope research

Cetaceans are unique ecological engineers, and their restoration may have a crucial impact on the future structure of aquatic ecosystems, which calls for more investigations into their trophic ecology. Among current techniques, stable isotope analysis (SIA) has the advantages of non-invasive sampling and long timescales. However, the full benefits of SIA in cetacean research may not be achieved due to issues like different types of tissue between sampling methods and use of chemical preservation solutions in historical specimens. To address these challenges, we conducted a study on Narrow-ridged Finless Porpoises (Neophocaena asiaeorientalis). Multiple tissues from freshwater and marine subspecies, as well as tissues preserved using different solutions such as ethanol and formalin were collected for SIA. Linear mixed effects models were used for data analysis. Our results showed that, except for blubber, kidney, and stomach, differences between other tissues were correctable. In tissues from live sampling, we found no significant difference between blood and muscle, and skin could also be used for isotope analysis after proper correction. Ethanol preservation caused significant positive changes in 813C and 815N values of muscle, while formalin preservation caused negative changes in 813C and 815N. Our findings provide valuable insight into unifying data from stranded carcasses and live sampling, as well as correcting for the effect of chemical preservation on museum specimens. Findings from this research support further application of stable isotope analysis in the conservation of endangered finless porpoises, offer a reference for other similar cetaceans, and also provide guidance for chemical preservation when freezing conditions are not available.