Interpretation of southern hemisphere humpback whale diet via stable isotopes; implications of tissue-specific analysis

Blubber and skin are commonly used tissues in stable isotope analysis for the purpose of investigating cetacean diet. Critical comparison of tissue-specific isotopic signals is, however, lacking resulting in uncertainty surrounding the representativeness and therefore utility of different tissues for accurate determination of recent foraging. This study used remotely biopsied blubber and skin tissues from southern hemisphere humpback whales for strategic comparison of delta C-13 and delta N-15 values. Samples were collected between 2008-2018 as part of long-term monitoring under the Humpback Whale Sentinel Program. Blubber tissues were lipid-extracted prior to analysis, whilst mathematical lipid-correction was performed on skin samples. Isotopic values from paired blubber and skin samples from the same individuals were compared to assess whether tissues could be used interchangeably for isotope analysis and dietary interpretation. Significant differences were observed for both delta C-13 and delta N-15, flagging previously undocumented methodological considerations, and the need for method validation and standardisation in application of these approaches. This study therefore advances methodological aspects of cetacean dietary analysis. This is of elevated importance in the context of rapidly changing ocean ecosystems.

Automated summary

This study compared the carbon and nitrogen isotopic values of blubber and skin tissues of Southern Hemisphere humpback whales, revealing significant differences between the two tissues. It highlights the need for method validation and standardization in the application of these approaches, advancing the methodological aspects of cetacean dietary analysis. This is of elevated importance in the context of rapidly changing ocean ecosystems.