Impact of freezing and ethanol preservation techniques on the stable isotope analysis of humpback whale (Megaptera novaeangliae) skin.

RESUMEN

RATIONALE: Distinct techniques employed to preserve different types of tissues may affect stable isotope analyses conducted on samples, and this is critical when field work takes place in remote areas. To investigate this, the stable isotope ratios (δ13 C and δ15 N values) obtained using two methods commonly used to preserve humpback whale (and other cetaceans) skin samples were compared. METHODS: A total of 54 pairs of skin samples of humpback whales from the southern Baja California Peninsula, Mexico, were preserved in ethanol (90%) and by freezing, between 2007 and 2009. The δ13 C and δ15 N values were determined using a PDZ Europa ANCA-GSL elemental analyzer interfaced to a PDZ Europe 20-20 isotope ratio mass spectrometer. Parametric and nonparametric tests were used to compare the isotopic results. RESULTS: A significant (t = 4.93; p = 0.000003) variation of −0.92‰ was found between the mean δ13 C values in ethanol (from −19.38‰ to −16.07‰; mean = −17.86‰) and freezing (from −20.67‰ to −16.44‰; mean = −18.78‰) techniques. No significant (U = 1314, p = 0.38) differences were observed in the δ15 N values. The δ13 C values were compared between preservation methods for each of the three years under analysis. Significant differences were observed in 2007 (t = 3.45; p = 0.0012) and 2008 (t = 3.13; p = 0.0030), but not for 2009 (t = 1.66; p = 0.12). CONCLUSIONS: Based on the results of this study, the use of ethanol to preserve humpback whale skin samples collected for stable isotope analysis is not recommended, particularly regarding the analysis of δ13 C values. This study serves as a point of reference for future research on humpback whales or other whales involving skin samples preserved by freezing or in ethanol.