Accounting for the effects of lipids in stable isotope (δ 13 C and δ 15 N values) analysis of skin and blubber of balaenopterid whales

• Published in: Rapid Communications in Mass Spectrometry
• Main Authors: Ryan, Conor, McHugh, B., Trueman, C.N., Harrod, C., Berrow, S.D., O'Connor, I.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: Balaenoptera physalus; Fin whale; Humpback Whale; Megaptera novaeangliae; minke whale
• Online Access: https://pure.qub.ac.uk/en/publications/1a48dcea-daf2-4a37-8b00-9b861be7ba8b; https://doi.org/10.1002/rcm.6394; http://www.scopus.com/inward/record.url?partnerID=yv4JPVwI&eid=2-s2.0-84868380617&md5=38dc56c05adbde5c69f99d1f12e81783

RATIONALE Stable isotope values (d 13 C and d 15 N) of darted skin and blubber biopsies can shed light on habitat use and diet of cetaceans, which are otherwise difficult to study. Non-dietary factors affect isotopic variability, chiefly the depletion of C due to the presence of C-rich lipids. The efficacy of post hoc lipid-correction models (normalization) must be tested. METHODS For tissues with high natural lipid content (e.g., whale skin and blubber), chemical lipid extraction or normalization is necessary. C:N ratios, d 13 C values and d 15 N values were determined for duplicate control and lipid-extracted skin and blubber of fin (Balaenoptera physalus), humpback (Megaptera novaeangliae) and minke whales (B. acutorostrata) by continuous-flow elemental analysis isotope ratio mass spectrometry (CF-EA-IRMS). Six different normalization models were tested to correct d 13 C values for the presence of lipids. RESULTS Following lipid extraction, significant increases in d 13 C values were observed for both tissues in the three species. Significant increases were also found for d 15 N values in minke whale skin and fin whale blubber. In fin whale skin, the d 15 N values decreased, with no change observed in humpback whale skin. Non-linear models generally out-performed linear models and the suitability of models varied by species and tissue, indicating the need for high model specificity, even among these closely related taxa. CONCLUSIONS Given the poor predictive power of the models to estimate lipid-free d13C values, and the unpredictable changes in d N values due to lipid-extraction, we recommend against arithmetical normalization in accounting for lipid effects on d13C values for balaenopterid skin or blubber samples. Rather, we recommend that duplicate analysis of lipid-extracted (d13C values) and non-treated tissues (d15N values) be used.