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

Abstract

Marine mammals and turtles are often studied using the carcasses of stranded deadindividuals. Since decomposition processes might modify the stable isotope ratios of tissues, thepresent study tested the effects of decomposition on carbon (δ13C) and nitrogen (δ15N) stable iso-tope ratios in 2 tissue types of striped dolphin Stenella coeruleoalbaand loggerhead sea turtleCaretta caretta. Decomposing carcasses of 3 dolphins and 3 turtles were sampled for muscle andskin 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 ambienttemperature, but no statistical change in δ13C or δ15N was observed over that period for either tis-sue or species. These results imply that muscle and skin samples from carcasses decomposing outof water at stage CC4 or lower can be used as reliable material for stable isotope analysis in these2 species, and probably in other marine mammal and marine turtle species. The effects of decom-position on the stability of stable isotope ratios in other tissues, in carcasses at stage CC5, or in car-casses decomposing underwater require further study.