Effect of tissue decomposition on stable isotope signatures of striped dolphins Stenella coeruleoalba and loggerhead sea turtles Caretta caretta

Marine mammals and turtles are often studied using the carcasses of stranded dead individuals. Since decomposition processes might modify the stable isotope ratios of tissues, the present study tested the effects of decomposition on carbon (delta C-13) and nitrogen (delta N-15) stable isotope ratios in 2 tissue types of striped dolphin Stenella coeruleoalba and loggerhead sea turtle Caretta caretta. Decomposing carcasses of 3 dolphins and 3 turtles were sampled for muscle and skin for 62 d. Following lipid extraction, samples were analysed regularly using a continuous flow-isotope ratio mass spectrometer. Samples reached decomposition stage CC4 after 62 d at ambient temperature, but no statistical change in delta C-13 or delta N-15 was observed over that period for either tissue or species. These results imply that muscle and skin samples from carcasses decomposing out of water at stage CC4 or lower can be used as reliable material for stable isotope analysis in these 2 species, and probably in other marine mammal and marine turtle species. The effects of decomposition on the stability of stable isotope ratios in other tissues, in carcasses at stage CC5, or in carcasses decomposing underwater require further study.