Does Decomposition Alter Stable Isotopic Values in Carcasses of Fur-Harvested Animals in a Boreal Climate?

Diet composition analyses such as stable isotope analyses are widely used to infer food sources in wild animals, reflecting assimilated dietary inputs in body tissues. Collecting tissue samples is often invasive and costly, making opportunistic sampling of animals captured for other purposes (hunting, fishing, trapping) particularly attractive. We thus aimed to assess whether the post-mortem handling commonly associated with fur-trapped mammals (freezing, thawing, and early decomposition) alters stable isotopic values of muscle tissue, thereby affecting their suitability for ecological studies. We used muscle tissue samples from coyotes (Canis latrans (Say, 1823)) harvested by trappers to investigate the effect of muscle decomposition on carbon (C) and nitrogen (N) stable isotopes ratios, and on C:N ratios. We sampled muscle tissue from four frozen carcasses that were kept outdoors at ambient temperature for a 10-day period. We found no effect of accumulated degree-days or time since start of trial on stable isotopic values. Our results suggest that samples from frozen trapped carcasses are suitable for isotopic analyses for up to 10 days or 82 accumulated degree-days post-mortem, especially under boreal climates where cool seasonal temperatures preserve tissue integrity. This underused and easily accessible source of samples represents a valuable opportunity for researchers.