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 (δ13C) and nitrogen (δ15N) 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 flowisotope

ratio mass spectrometer. Samples reached decomposition stage CC4 after 62 d at ambient

temperature, but no statistical change in δ13C or δ15N 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.