Ryan (2020) states that Christiansen et al. (2020) ‘compellingly argue that blubber lipid-content measurements could inform health and life-history assessments of humpback whales’. Rather, the manuscript poses that body condition (not lipid% specifically) can yield important information about humpback whale life history and health. Blubber lipid content has historically been used as an indirect proxy for body condition, as has body morphometry measures obtained by photogrammetry. Methodological comparisons, such as those performed in this study, are imperative for advancing robust body condition evaluation and are much needed for evaluating the strengths and limitations of respective approaches, and hereby directing researchers towards the most appropriate methods for new investigations (Castrillon and Bengtson Nash, 2020).

Ryan succinctly summarises the sampling artefacts associated with ascertaining blubber lipid% by remotely biopsied blubber tissue. The authors are in complete agreement with Ryan on this point and indeed dedicate the latter part of the discussion (4th paragraph) to outlining the role of such artefacts as possible confounding factors in the lack of any observable correspondence between photogrammetry and blubber lipid measures in the current study. Importantly, the remotely biopsied tissues analysed in the current study were sub-divided for seven different biochemical and chemical tracer analyses, of which lipid% was merely one, demonstrating the value of the remote biopsy approach for cetacean research and health assessment.

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