An evaluation of lipid extraction techniques for interpretation of carbon and nitrogen isotope values in bottlenose dolphin ( Tursiops truncatus ) skin tissue

Abstract

We studied the effects of two common chemical extraction techniques on bottlenose dolphin ( Tursiops truncatus ) skin tissues with the intent to develop a mathematical lipid correction for dolphin skin δ 13 C. One method employs a hot solvent mixture (chloroform and methanol) while the other method requires washing the samples with cold solvent followed by water. The water wash method resulted in significant alteration of tissue δ 15 N. We found no correlation between change in sample mass and C/N or between change in sample mass and the change in δ 13 C (Δδ 13 C) following lipid extraction. Although Δδ 13 C was positive following lipid extraction (mean = 1.6‰ and 1.2‰, for the two methods), there was no correlation between C/N and Δδ 13 C for either method. Cumulatively, these results prevented us from applying a mathematical lipid normalization. Based on our findings and consideration of previously reported results, we suggest that applying these extraction techniques to dolphin skin with C/N 13 C needs to be accounted for when implementing isotope mixing models to assess diet or organic matter sources.

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