![]() ![]() The interpretation of bulk stable isotope (BSI) signals is, however, not without uncertainty. Over the last few decades, BSIA has played a significant role in research involving animal migration, diet, reproduction and food web connectivity. Longitudinal monitoring of SHHW diet has therefore been identified as a core sentinel parameter under the Humpback Whale Sentinel Program (HWSP), with interannual variation and drift assumed to reflect a change in krill availability.Įcologists use bulk stable isotope analysis (BSIA) to directly identify and trace elemental cycling in the biosphere. As such, SHHWs may be expected to respond to a change in krill availability through diversified foraging, including changes to both prey and foraging range. ![]() Humpback whale (HW) populations globally show a high degree of plasticity in both their target prey and foraging behaviour. Any change in the abundance and/or availability of krill is expected to carry significant implications for krill consumers. Kill rely on a stable physio-chemical sea-ice environment and changes can impact krill recruitment and survival. Polar ecosystems are undergoing rapid change, manifesting in sea-ice melt, ocean acidification, and a rise in sea water temperature. Krill are a sympagic species, where sea-ice provides feeding habitats and refuge for early life stages. Their ecophysiology thus renders these populations powerful indicators of ecosystem productivity and change. The narrow foraging niche of SHHWs results in a distilled connection between ecosystem productivity and energetic provisioning (both prey type and foraging success Castrillon and Bengtson Nash. As capital breeders, these populations rely on intensive summer feeding on Antarctic krill ( Euphausia superba hereafter ‘krill’, to sustain their annual winter migrations to lower latitudes for breeding and calving. Southern hemisphere humpback whales ( Megaptera novaeangliae SHHWs) have been implemented as a sentinel species for the circumpolar surveillance of pollution and climate change in the Southern Ocean. This is of elevated importance in the context of rapidly changing ocean ecosystems. This study therefore advances methodological aspects of cetacean dietary analysis. ![]() Significant differences were observed for both δ 13C and δ 15N, flagging previously undocumented methodological considerations, and the need for method validation and standardisation in application of these approaches. 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. Blubber tissues were lipid-extracted prior to analysis, whilst mathematical lipid-correction was performed on skin samples. Samples were collected between 2008–2018 as part of long-term monitoring under the Humpback Whale Sentinel Program. This study used remotely biopsied blubber and skin tissues from southern hemisphere humpback whales for strategic comparison of δ 13C and δ 15N values. 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. Blubber and skin are commonly used tissues in stable isotope analysis for the purpose of investigating cetacean diet. ![]()
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