Use of biopsy samples of humpback whale (Megaptera novaeangliae) skin for stable isotope (δ¹³C) determination

Previous work has shown that stable isotope indicators taken from the muscle tissue of dead, stranded cetaceans can be used to assess diet. Recent advances in remote biopsy techniques have provided a means to collect skin and blubber tissues from live animals. This study examines the potential of biopsy samples taken from humpback whales (Megaptera novaeangliae) for isotopic assessments of diet by: 1) determining if isotopic differences exist between the two tissue types obtained in a biopsy (skin and blubber) and the traditional source for isotopic analysis, muscle tissue, 2) examining the effects of two different lipid extraction techniques on the removal of the preservative dimethyl sulfphoxide (DMSO) from tissues, and 3) assessing procedural reproducibility for automated isotopic analysis of skin derived from biopsy samples. Results demonstrate that carbon isotopic values (δ¹³C) of muscle were not significantly different from those of skin (Scheffe, p = 0.4985; δ¹³C = 19.1‰ ± 0.5 for muscle and skin respectively; mean ± SD). The values for blubber (δ¹³C = -23.7‰ ± 0.2) were significantly lower than those of muscle of skin (Scheffe, p = 0.0001). This result was consistent with previous studies indicating that the δ¹³C of lipids is typically lighter than those tissues with which it is associated. The analysis also indicates that samples preserved in DMSO have significantly lower δ¹³C than unpreserved samples (paired t-test, p = 0.010). Two methods of lipid extraction, sonication and Soxhlet extraction, were successful in removing DMSO from samples. The procedural reproducibility for δ¹³C was 0.1‰. In summary, skin tissue yielded from biopsy samples may be used in isotopic assessments of diet. The use of biopsies as a source allows the technique to be used in longitudinal, non-lethal sampling.